Publications by authors named "Jeffrey N Agar"

55 Publications

Increasing Top-Down Mass Spectrometry Sequence Coverage by an Order of Magnitude through Optimized Internal Fragment Generation and Assignment.

Anal Chem 2021 Apr 12. Epub 2021 Apr 12.

Department of Chemistry and Chemical Biology, Northeastern University, Boston, Massachusetts 02115, United States.

A major limitation of intact protein fragmentation is the lack of sequence coverage within proteins' interiors. We show that collisionally activated dissociation (CAD) produces extensive internal fragmentation within proteins' interiors that fill the existing gaps in sequence coverage, including disulfide loop regions that cannot be characterized using terminal fragments. A barrier to the adoption of internal fragments is the lack of methods for their generation and assignment. To provide these, we explore the effects of protein size, mass accuracy, internal fragment size, CAD activation energy, and data preprocessing upon the production and identification of internal fragments. We also identify and mitigate the major source of ambiguity in internal fragment identification, which we term "frameshift ambiguity." Such ambiguity results from sequences containing any "middle" portion surrounded by the same composition on both termini, which upon fragmentation can produce two internal fragments of identical mass, yet out of frame by one or more amino acids (e.g., TRAIT producing TRAI or RAIT). We show that such instances permit the a priori assignment of the middle sequence portion. This insight and our optimized methods permit the unambiguous assignment of greater than 97% of internal fragments using only the accurate mass. We show that any remaining ambiguity in internal fragment assignment can be removed by consideration of fragmentation propensities or by (pseudo)-MS. Applying these methods resulted in a 10-fold and 43-fold expanded number of identified ions, and a concomitant 7- and 16-fold increase in fragmentation sites, respectively, for native and reduced forms of a disease-associated SOD1 variant.
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http://dx.doi.org/10.1021/acs.analchem.0c04670DOI Listing
April 2021

Raf promotes dimerization of the Ras G-domain with increased allosteric connections.

Proc Natl Acad Sci U S A 2021 Mar;118(10)

Department of Chemistry and Chemical Biology, Northeastern University, Boston, MA 02115;

Ras dimerization is critical for Raf activation. Here we show that the Ras binding domain of Raf (Raf-RBD) induces robust Ras dimerization at low surface densities on supported lipid bilayers and, to a lesser extent, in solution as observed by size exclusion chromatography and confirmed by SAXS. Community network analysis based on molecular dynamics simulations shows robust allosteric connections linking the two Raf-RBD D113 residues located in the Galectin scaffold protein binding site of each Raf-RBD molecule and 85 Å apart on opposite ends of the dimer complex. Our results suggest that Raf-RBD binding and Ras dimerization are concerted events that lead to a high-affinity signaling complex at the membrane that we propose is an essential unit in the macromolecular assembly of higher order Ras/Raf/Galectin complexes important for signaling through the Ras/Raf/MEK/ERK pathway.
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http://dx.doi.org/10.1073/pnas.2015648118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7958358PMC
March 2021

Cyclic Thiosulfinates as a Novel Class of Disulfide Cleavable Cross-Linkers for Rapid Hydrogel Synthesis.

Bioconjug Chem 2021 Mar 19;32(3):584-594. Epub 2021 Feb 19.

Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States.

We recently reported that cyclic thiosulfinates are cysteine selective cross-linkers that avoid the "dead-end" modifications that contribute to other cross-linkers' toxicity. In this study, we generalize the chemistry of cyclic thiosulfinates to that of thiol selective cross-linking and apply them to the synthesis of hydrogels. Thiol-functionalized four-arm poly(ethylene glycol) and hyaluronic acid monomers were cross-linked with 1,2-dithiane-1-oxide to form disulfide cross-linked hydrogels within seconds. The synthesized hydrogel could be reduced with physiological concentrations of glutathione, which modulated hydrogel mechanical properties and degradation kinetics. Bovine serum albumin protein was successfully encapsulated in hydrogel, and diffusion-mediated release was demonstrated in vitro. Hep G2 cells grew in the presence of preformed hydrogel and during hydrogel synthesis, demonstrating acceptable cytotoxicity. We encapsulated cells within a hydrogel and demonstrated cell growth and recovery up to 10 days, with and without cell adhesion peptides. In summary, we report cyclic thiosulfinates as a novel class of cross-linkers for the facile synthesis of biodegradable hydrogels.
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http://dx.doi.org/10.1021/acs.bioconjchem.1c00049DOI Listing
March 2021

Spatial Distribution of Transcytosis Relevant Phospholipids in Response to Omega-3 Dietary Deprivation.

ACS Chem Biol 2021 01 14;16(1):106-115. Epub 2020 Dec 14.

Department of Neurosurgery, Brigham and Woman's Hospital, Harvard Medical School, Boston, Massachusetts 02115-6195, United States.

The cell membrane of brain endothelial cells is enriched in omega-3 phospholipid species. Numerous omega-3 phospholipid species were recently proposed to be important for maintaining the low rate of transcytosis and, thus, could be important for regulating one of the mechanisms of the blood brain barrier (BBB). However, the spatial distribution of these phospholipid species within the brain was previously unknown. Here, we combined advanced mass spectrometry imaging techniques to generate a map of these phospholipids in the brain at near single cell resolution. Furthermore, we explored the effects of omega-3 dietary deprivation on both docosahexaenoic acid (DHA)-containing phospholipids and the global brain phospholipid profile. We demonstrate the unique spatial distribution of individual DHA-containing phospholipids, which may be important for the regiospecific properties of the BBB. Finally, 24 diet discriminative phospholipids were identified and showed an increase in saturated phospholipid species and ceramide containing phospholipid species under omega-3 dietary deficiency.
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http://dx.doi.org/10.1021/acschembio.0c00779DOI Listing
January 2021

Interlaboratory Study for Characterizing Monoclonal Antibodies by Top-Down and Middle-Down Mass Spectrometry.

J Am Soc Mass Spectrom 2020 Sep 19;31(9):1783-1802. Epub 2020 Aug 19.

Pacific Northwest National Laboratory, Richland, Washington 99354, United States.

The Consortium for Top-Down Proteomics (www.topdownproteomics.org) launched the present study to assess the current state of top-down mass spectrometry (TD MS) and middle-down mass spectrometry (MD MS) for characterizing monoclonal antibody (mAb) primary structures, including their modifications. To meet the needs of the rapidly growing therapeutic antibody market, it is important to develop analytical strategies to characterize the heterogeneity of a therapeutic product's primary structure accurately and reproducibly. The major objective of the present study is to determine whether current TD/MD MS technologies and protocols can add value to the more commonly employed bottom-up (BU) approaches with regard to confirming protein integrity, sequencing variable domains, avoiding artifacts, and revealing modifications and their locations. We also aim to gather information on the common TD/MD MS methods and practices in the field. A panel of three mAbs was selected and centrally provided to 20 laboratories worldwide for the analysis: Sigma mAb standard (SiLuLite), NIST mAb standard, and the therapeutic mAb Herceptin (trastuzumab). Various MS instrument platforms and ion dissociation techniques were employed. The present study confirms that TD/MD MS tools are available in laboratories worldwide and provide complementary information to the BU approach that can be crucial for comprehensive mAb characterization. The current limitations, as well as possible solutions to overcome them, are also outlined. A primary limitation revealed by the results of the present study is that the expert knowledge in both experiment and data analysis is indispensable to practice TD/MD MS.
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http://dx.doi.org/10.1021/jasms.0c00036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7539639PMC
September 2020

Loss of angiogenin function is related to earlier ALS onset and a paradoxical increase in ALS duration.

Sci Rep 2020 02 28;10(1):3715. Epub 2020 Feb 28.

Barnett Institute of Chemical and Biological Analysis, Northeastern University, Boston, MA, 02115, USA.

0.5-1% of ALS (Amyotrophic Lateral Sclerosis) and Parkinson's disease (PD) are associated with mutations in the angiogenin (ANG). These mutations are thought to cause disease through a loss of ANG function, but this hypothesis has not been evaluated statistically. In addition, the potential for ANG to promote disease has not been considered. With the goal of better defining the etiology of ANG-ALS, we assembled all clinical onset and disease duration data and determined if these were correlated with biochemical properties of ANG variants. Loss of ANG stability and ribonuclease activity were found to correlate with early ALS onset, confirming an aspect of the prevailing model of ANG-ALS. Conversely, loss of ANG stability and ribonuclease activity correlated with longer survival following diagnosis, which is inconsistent with the prevailing model. These results indicate that functional ANG appears to decrease the risk of developing ALS but exacerbate ALS once in progress. These findings are rationalized in terms of studies demonstrating that distinct mechanisms contribute to ALS onset and progression and propose that ANG replacement or stabilization would benefit pre-symptomatic ANG-ALS patients. However, this study challenges the prevailing hypothesis that augmenting ANG will benefit symptomatic ANG-ALS patients. Instead, our results suggest that silencing of ANG activity may be beneficial for symptomatic ALS patients. This study will serve as a call-to-arms for neurologists to consistently publish ALS and PD patient's clinical data-if all ANG-ALS patients' data were available our findings could be tested with considerable statistical power.
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http://dx.doi.org/10.1038/s41598-020-60431-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7048737PMC
February 2020

Localized Metabolomic Gradients in Patient-Derived Xenograft Models of Glioblastoma.

Cancer Res 2020 03 25;80(6):1258-1267. Epub 2019 Nov 25.

Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts.

Glioblastoma (GBM) is increasingly recognized as a disease involving dysfunctional cellular metabolism. GBMs are known to be complex heterogeneous systems containing multiple distinct cell populations and are supported by an aberrant network of blood vessels. A better understanding of GBM metabolism, its variation with respect to the tumor microenvironment, and resulting regional changes in chemical composition is required. This may shed light on the observed heterogeneous drug distribution, which cannot be fully described by limited or uneven disruption of the blood-brain barrier. In this work, we used mass spectrometry imaging (MSI) to map metabolites and lipids in patient-derived xenograft models of GBM. A data analysis workflow revealed that distinctive spectral signatures were detected from different regions of the intracranial tumor model. A series of long-chain acylcarnitines were identified and detected with increased intensity at the tumor edge. A 3D MSI dataset demonstrated that these molecules were observed throughout the entire tumor/normal interface and were not confined to a single plane. mRNA sequencing demonstrated that hallmark genes related to fatty acid metabolism were highly expressed in samples with higher acylcarnitine content. These data suggest that cells in the core and the edge of the tumor undergo different fatty acid metabolism, resulting in different chemical environments within the tumor. This may influence drug distribution through changes in tissue drug affinity or transport and constitute an important consideration for therapeutic strategies in the treatment of GBM. SIGNIFICANCE: GBM tumors exhibit a metabolic gradient that should be taken into consideration when designing therapeutic strategies for treatment..
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http://dx.doi.org/10.1158/0008-5472.CAN-19-0638DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7073296PMC
March 2020

Dysregulation of very-long-chain fatty acid metabolism causes membrane saturation and induction of the unfolded protein response.

Mol Biol Cell 2020 01 20;31(1):7-17. Epub 2019 Nov 20.

Department of Pathology and.

The unfolded protein response (UPR) senses defects in the endoplasmic reticulum (ER) and orchestrates a complex program of adaptive cellular remodeling. Increasing evidence suggests an important relationship between lipid homeostasis and the UPR. Defects in the ER membrane induce the UPR, and the UPR in turn controls the expression of some lipid metabolic genes. Among lipid species, the very-long-chain fatty acids (VLCFAs) are relatively rare and poorly understood. Here, we show that loss of the VLCFA-coenzyme A synthetase Fat1, which is essential for VLCFA utilization, results in ER stress with compensatory UPR induction. Comprehensive lipidomic analyses revealed a dramatic increase in membrane saturation in the mutant, likely accounting for UPR induction. In principle, this increased membrane saturation could reflect adaptive membrane remodeling or an adverse effect of VLCFA dysfunction. We provide evidence supporting the latter, as the mutant showed defects in the function of Ole1, the sole fatty acyl desaturase in yeast. These results indicate that VLCFAs play essential roles in protein quality control and membrane homeostasis and suggest an unexpected requirement for VLCFAs in Ole1 function.
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http://dx.doi.org/10.1091/mbc.E19-07-0392DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6938273PMC
January 2020

Best practices and benchmarks for intact protein analysis for top-down mass spectrometry.

Nat Methods 2019 07 27;16(7):587-594. Epub 2019 Jun 27.

Barnett Institute of Chemical and Biological Analysis and Departments of Chemistry & Chemical Biology and Pharmaceutical Sciences, Northeastern University, Boston, MA, USA.

One gene can give rise to many functionally distinct proteoforms, each of which has a characteristic molecular mass. Top-down mass spectrometry enables the analysis of intact proteins and proteoforms. Here members of the Consortium for Top-Down Proteomics provide a decision tree that guides researchers to robust protocols for mass analysis of intact proteins (antibodies, membrane proteins and others) from mixtures of varying complexity. We also present cross-platform analytical benchmarks using a protein standard sample, to allow users to gauge their proficiency.
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http://dx.doi.org/10.1038/s41592-019-0457-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6719561PMC
July 2019

Automatic 3D Nonlinear Registration of Mass Spectrometry Imaging and Magnetic Resonance Imaging Data.

Anal Chem 2019 05 22;91(9):6206-6216. Epub 2019 Apr 22.

Department of Neurosurgery, Brigham and Women's Hospital , Harvard Medical School , Boston , Massachusetts 02115 , United States.

Multimodal integration between mass spectrometry imaging (MSI) and radiology-established modalities such as magnetic resonance imaging (MRI) would allow the investigations of key questions in complex biological systems such as the central nervous system. Such integration would provide complementary multiscale data to bridge the gap between molecular and anatomical phenotypes, potentially revealing new insights into molecular mechanisms underlying anatomical pathologies presented on MRI. Automatic coregistration between 3D MSI/MRI is a computationally challenging process due to dimensional complexity, MSI data sparsity, lack of direct spatial-correspondences, and nonlinear tissue deformation. Here, we present a new computational approach based on stochastic neighbor embedding to nonlinearly align 3D MSI to MRI data, identify and reconstruct biologically relevant molecular patterns in 3D, and fuse the MSI datacube to the MRI space. We demonstrate our method using multimodal high-spectral resolution matrix-assisted laser desorption ionization (MALDI) 9.4 T MSI and 7 T in vivo MRI data, acquired from a patient-derived, xenograft mouse brain model of glioblastoma following administration of the EGFR inhibitor drug of Erlotinib. Results show the distribution of some identified molecular ions of the EGFR inhibitor erlotinib, a phosphatidylcholine lipid, and cholesterol, which were reconstructed in 3D and mapped to the MRI space. The registration quality was evaluated on two normal mouse brains using the Dice coefficient for the regions of brainstem, hippocampus, and cortex. The method is generic and can therefore be applied to hyperspectral images from different mass spectrometers and integrated with other established in vivo imaging modalities such as computed tomography (CT) and positron emission tomography (PET).
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http://dx.doi.org/10.1021/acs.analchem.9b00854DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6691508PMC
May 2019

Genetically Encoded Fluorescent Proteins Enable High-Throughput Assignment of Cell Cohorts Directly from MALDI-MS Images.

Anal Chem 2019 03 6;91(6):3810-3817. Epub 2019 Mar 6.

Department of Chemistry and Chemical Biology and Barnett Institute of Chemical and Biological Analysis , Northeastern University , Boston , Massachusetts 02115 , United States.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) provides a unique in situ chemical profile that can include drugs, nucleic acids, metabolites, lipids, and proteins. MSI of individual cells (of a known cell type) affords a unique insight into normal and disease-related processes and is a prerequisite for combining the results of MSI and other single-cell modalities (e.g. mass cytometry and next-generation sequencing). Technological barriers have prevented the high-throughput assignment of MSI spectra from solid tissue preparations to their cell type. These barriers include obtaining a suitable cell-identifying image (e.g. immunohistochemistry) and obtaining sufficiently accurate registration of the cell-identifying and MALDI-MS images. This study introduces a technique that overcame these barriers by assigning cell type directly from mass spectra. We hypothesized that, in MSI from mice with a defined fluorescent protein expression pattern, the fluorescent protein's molecular ion could be used to identify cell cohorts. A method was developed for the purification of enhanced yellow fluorescent protein (EYFP) from mice. To determine EYFP's molecular mass for MSI studies, we performed intact mass analysis and characterized the protein's primary structure and post-translational modifications through various techniques. MALDI-MSI methods were developed to enhance the detection of EYFP in situ, and by extraction of EYFP's molecular ion from MALDI-MS images, automated, whole-image assignment of cell cohorts was achieved. This method was validated using a well-characterized mouse line that expresses EYFP in motor and sensory neurons and should be applicable to hundreds of commercially available mice (and other animal) strains comprising a multitude of cell-specific fluorescent labels.
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http://dx.doi.org/10.1021/acs.analchem.8b03454DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6827431PMC
March 2019

Molecular Characterization of Prostate Cancer with Associated Gleason Score Using Mass Spectrometry Imaging.

Mol Cancer Res 2019 05 11;17(5):1155-1165. Epub 2019 Feb 11.

Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts.

Diagnosis of prostate cancer is based on histologic evaluation of tumor architecture using a system known as the "Gleason score." This diagnostic paradigm, while the standard of care, is time-consuming, shows intraobserver variability, and provides no information about the altered metabolic pathways, which result in altered tissue architecture. Characterization of the molecular composition of prostate cancer and how it changes with respect to the Gleason score (GS) could enable a more objective and faster diagnosis. It may also aid in our understanding of disease onset and progression. In this work, we present mass spectrometry imaging for identification and mapping of lipids and metabolites in prostate tissue from patients with known prostate cancer with GS from 6 to 9. A gradient of changes in the intensity of various lipids was observed, which correlated with increasing GS. Interestingly, these changes were identified in both regions of high tumor cell density, and in regions of tissue that appeared histologically benign, possibly suggestive of precancerous metabolomic changes. A total of 31 lipids, including several phosphatidylcholines, phosphatidic acids, phosphatidylserines, phosphatidylinositols, and cardiolipins were detected with higher intensity in GS (4+3) compared with GS (3+4), suggesting they may be markers of prostate cancer aggression. Results obtained through mass spectrometry imaging studies were subsequently correlated with a fast, ambient mass spectrometry method for potential use as a clinical tool to support image-guided prostate biopsy. IMPLICATIONS: In this study, we suggest that metabolomic differences between prostate cancers with different Gleason scores can be detected by mass spectrometry imaging.
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http://dx.doi.org/10.1158/1541-7786.MCR-18-1057DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6497547PMC
May 2019

Integrated mapping of pharmacokinetics and pharmacodynamics in a patient-derived xenograft model of glioblastoma.

Nat Commun 2018 11 21;9(1):4904. Epub 2018 Nov 21.

Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, 02115, USA.

Therapeutic options for the treatment of glioblastoma remain inadequate despite concerted research efforts in drug development. Therapeutic failure can result from poor permeability of the blood-brain barrier, heterogeneous drug distribution, and development of resistance. Elucidation of relationships among such parameters could enable the development of predictive models of drug response in patients and inform drug development. Complementary analyses were applied to a glioblastoma patient-derived xenograft model in order to quantitatively map distribution and resulting cellular response to the EGFR inhibitor erlotinib. Mass spectrometry images of erlotinib were registered to histology and magnetic resonance images in order to correlate drug distribution with tumor characteristics. Phosphoproteomics and immunohistochemistry were used to assess protein signaling in response to drug, and integrated with transcriptional response using mRNA sequencing. This comprehensive dataset provides simultaneous insight into pharmacokinetics and pharmacodynamics and indicates that erlotinib delivery to intracranial tumors is insufficient to inhibit EGFR tyrosine kinase signaling.
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http://dx.doi.org/10.1038/s41467-018-07334-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6249307PMC
November 2018

Rapid discrimination of pediatric brain tumors by mass spectrometry imaging.

J Neurooncol 2018 Nov 20;140(2):269-279. Epub 2018 Aug 20.

Winship Cancer Institute, Emory University School of Medicine, 1365C Clifton Road, Suite C5086, Atlanta, GA, 30322, USA.

Purpose: Medulloblastoma, the most common primary pediatric malignant brain tumor, originates in the posterior fossa of the brain. Pineoblastoma, which originates within the pineal gland, is a rarer malignancy that also presents in the pediatric population. Medulloblastoma and pineoblastoma exhibit overlapping clinical features and have similar histopathological characteristics. Histopathological similarities confound rapid diagnoses of these two tumor types. We have conducted a pilot feasibility study analyzing the molecular profile of archived frozen human tumor specimens using mass spectrometry imaging (MSI) to identify potential biomarkers capable of classifying and distinguishing between medulloblastoma and pineoblastoma.

Methods: We performed matrix-assisted laser desorption ionization Fourier transform ion cyclotron resonance mass spectrometry imaging on eight medulloblastoma biopsy specimens and three pineoblastoma biopsy specimens. Multivariate statistical analyses were performed on the MSI dataset to generate classifiers that distinguish the two tumor types. Lastly, the molecules that were discriminative of tumor type were queried against the Lipid Maps database and identified.

Results: In this pilot study we show that medulloblastoma and pineoblastoma can be discriminated using molecular profiles determined by MSI. The highest-ranking discriminating classifiers of medulloblastoma and pineoblastoma were glycerophosphoglycerols and sphingolipids, respectively.

Conclusion: We demonstrate proof-of-concept that medulloblastoma and pineoblastoma can be rapidly distinguished by using MSI lipid profiles. We identified biomarker candidates capable of distinguishing these two histopathologically similar tumor types. This work expands the current molecular knowledge of medulloblastoma and pineoblastoma by characterizing their lipidomic profiles, which may be useful for developing novel diagnostic, prognostic and therapeutic strategies.
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http://dx.doi.org/10.1007/s11060-018-2978-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6244779PMC
November 2018

Cyclic Thiosulfinates and Cyclic Disulfides Selectively Cross-Link Thiols While Avoiding Modification of Lone Thiols.

J Am Chem Soc 2018 06 11;140(24):7377-7380. Epub 2018 Jun 11.

Department of Chemistry and Chemical Biology , Northeastern University , 360 Huntington Avenue , Boston , Massachusetts 02115 , United States.

This work addresses the need for chemical tools that can selectively form cross-links. Contemporary thiol-selective cross-linkers, for example, modify all accessible thiols, but only form cross-links between a subset. The resulting terminal "dead-end" modifications of lone thiols are toxic, confound cross-linking-based studies of macromolecular structure, and are an undesired, and currently unavoidable, byproduct in polymer synthesis. Using the thiol pair of Cu/Zn-superoxide dismutase (SOD1), we demonstrated that cyclic disulfides, including the drug/nutritional supplement lipoic acid, efficiently cross-linked thiol pairs but avoided dead-end modifications. Thiolate-directed nucleophilic attack upon the cyclic disulfide resulted in thiol-disulfide exchange and ring cleavage. The resulting disulfide-tethered terminal thiolate moiety either directed the reverse reaction, releasing the cyclic disulfide, or participated in oxidative disulfide (cross-link) formation. We hypothesized, and confirmed with density functional theory (DFT) calculations, that mono- S-oxo derivatives of cyclic disulfides formed a terminal sulfenic acid upon ring cleavage that obviated the previously rate-limiting step, thiol oxidation, and accelerated the new rate-determining step, ring cleavage. Our calculations suggest that the origin of accelerated ring cleavage is improved frontier molecular orbital overlap in the thiolate-disulfide interchange transition. Five- to seven-membered cyclic thiosulfinates were synthesized and efficiently cross-linked up to 10-fold faster than their cyclic disulfide precursors; functioned in the presence of biological concentrations of glutathione; and acted as cell-permeable, potent, tolerable, intracellular cross-linkers. This new class of thiol cross-linkers exhibited click-like attributes including, high yields driven by the enthalpies of disulfide and water formation, orthogonality with common functional groups, water-compatibility, and ring strain-dependence.
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http://dx.doi.org/10.1021/jacs.8b01136DOI Listing
June 2018

In Vitro Liquid Extraction Surface Analysis Mass Spectrometry (ivLESA-MS) for Direct Metabolic Analysis of Adherent Cells in Culture.

Anal Chem 2018 04 2;90(8):4987-4991. Epub 2018 Apr 2.

Department of Cancer Biology , Dana-Farber Cancer Institute, Harvard Medical School , Boston , Massachusetts 02115 , United States.

Conventional metabolomic methods include extensive sample preparation steps and long analytical run times, increasing the likelihood of processing artifacts and limiting high throughput applications. We present here in vitro liquid extraction surface analysis mass spectrometry (ivLESA-MS), a variation on LESA-MS, performed directly on adherent cells grown in 96-well cell culture plates. To accomplish this, culture medium was aspirated immediately prior to analysis, and metabolites were extracted using LESA from the cell monolayer surface, followed by nano-electrospray ionization and MS analysis in negative ion mode. We applied this platform to characterize and compare lipidomic profiles of multiple breast cancer cell lines growing in culture (MCF-7, ZR-75-1, MDA-MB-453, and MDA-MB-231) and revealed distinct and reproducible lipidomic signatures between the cell lines. Additionally, we demonstrated time-dependent processing artifacts, underscoring the importance of immediate analysis. ivLESA-MS represents a rapid in vitro metabolomic method, which precludes the need for quenching, cell harvesting, sample preparation, and chromatography, significantly shortening preparation and analysis time while minimizing processing artifacts. This method could be further adapted to test drugs in vitro in a high throughput manner.
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http://dx.doi.org/10.1021/acs.analchem.8b00530DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6196362PMC
April 2018

How many human proteoforms are there?

Nat Chem Biol 2018 02;14(3):206-214

Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, USA.

Despite decades of accumulated knowledge about proteins and their post-translational modifications (PTMs), numerous questions remain regarding their molecular composition and biological function. One of the most fundamental queries is the extent to which the combinations of DNA-, RNA- and PTM-level variations explode the complexity of the human proteome. Here, we outline what we know from current databases and measurement strategies including mass spectrometry-based proteomics. In doing so, we examine prevailing notions about the number of modifications displayed on human proteins and how they combine to generate the protein diversity underlying health and disease. We frame central issues regarding determination of protein-level variation and PTMs, including some paradoxes present in the field today. We use this framework to assess existing data and to ask the question, "How many distinct primary structures of proteins (proteoforms) are created from the 20,300 human genes?" We also explore prospects for improving measurements to better regularize protein-level biology and efficiently associate PTMs to function and phenotype.
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http://dx.doi.org/10.1038/nchembio.2576DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5837046PMC
February 2018

ProForma: A Standard Proteoform Notation.

J Proteome Res 2018 03 14;17(3):1321-1325. Epub 2018 Feb 14.

Spectroswiss , 1015 Lausanne, Switzerland.

The Consortium for Top-Down Proteomics (CTDP) proposes a standardized notation, ProForma, for writing the sequence of fully characterized proteoforms. ProForma provides a means to communicate any proteoform by writing the amino acid sequence using standard one-letter notation and specifying modifications or unidentified mass shifts within brackets following certain amino acids. The notation is unambiguous, human-readable, and can easily be parsed and written by bioinformatic tools. This system uses seven rules and supports a wide range of possible use cases, ensuring compatibility and reproducibility of proteoform annotations. Standardizing proteoform sequences will simplify storage, comparison, and reanalysis of proteomic studies, and the Consortium welcomes input and contributions from the research community on the continued design and maintenance of this standard.
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http://dx.doi.org/10.1021/acs.jproteome.7b00851DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5837035PMC
March 2018

Secretion, isotopic labeling and deglycosylation of N-acylethanolamine acid amidase for biophysical studies.

Protein Expr Purif 2018 05 15;145:108-117. Epub 2017 Dec 15.

Center for Drug Discovery, Department of Pharmaceutical Sciences, Department of Chemistry, Chemical Biology, Northeastern University, Boston, MA, 02115-5000, United States; King Abdulaziz University, Jeddah, 22254, Saudi Arabia.

N-acylethanolamine acid amidase (NAAA) is an N-terminal nucleophile (Ntn) enzyme with a catalytic cysteine residue that has highest activity at acidic pH. The most prominent substrate hydrolyzed is palmitoylethanolamine (PEA), which regulates inflammation. Inhibitors of NAAA have been shown to increase endogenous levels of PEA, and are of interest as potential treatments for inflammatory disorders and other maladies. Currently, there are no X-ray or NMR structures of NAAA available to inform medicinal chemistry. Additionally, there are a limited number of enzyme structures available that are within the Ntn-hydrolase family, have a catalytic cysteine residue, and have a high sequence homology. For these reasons, we developed expression and purification methods for the production of enzyme samples amenable to structural characterization. Mammalian cells are necessary for post-translational processing, including signal sequence cleavage and glycosylation, that are required for a correctly folded zymogen before conversion to active, and mature enzyme. We have identified an expression construct, mammalian cell line, specific media and additives to express and secrete hNAAA zymogen and we further optimized propagation conditions and show this secretion method is suitable for isotopic labeling of the protein. We refined purification methods to achieve a high degree of protein purity potentially suited to crystallography. Glycosylated proteins can present challenges to biophysical methods. Therefore we deglycosylate the enzyme and show that the activity of the mature enzyme is not affected by deglycosylation.
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http://dx.doi.org/10.1016/j.pep.2017.12.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6022831PMC
May 2018

Heavy Sugar and Heavy Water Create Tunable Intact Protein Mass Increases for Quantitative Mass Spectrometry in Any Feed and Organism.

Anal Chem 2016 11 28;88(22):11139-11146. Epub 2016 Oct 28.

Department of Chemistry and Chemical Biology, Northeastern University , 360 Huntington Avenue, Boston, Massachusetts 02115, United States.

Stable isotope labeling techniques for quantitative top-down proteomics face unique challenges. These include unpredictable mass shifts following isotope labeling, which impedes analysis of unknown proteins and complex mixtures and exponentially greater susceptibility to incomplete isotope incorporation, manifesting as broadening of labeled intact protein peaks. Like popular bottom-up isotope labeling techniques, most top-down labeling methods are restricted to defined media/feed as well as amino acid auxotrophic organisms. We present a labeling method optimized for top-down proteomics that overcomes these challenges. We demonstrated this method through the spiking of C-sugar or H-water into standard laboratory feedstocks, resulting in tunable intact protein mass increases (TIPMI). After mixing of labeled and unlabeled samples, direct comparison of light and heavy peaks allowed for the relative quantitation of intact proteins in three popular model organisms, including prokaryotic and eukaryotic microorganisms and an animal. This internal standard method proved to be more accurate than label-free quantitation in our hands. Advantages over top-down SILAC include working equally well in nutrient-rich media, conceivably expanding applicability to any organism and all classes of biomolecules, not requiring high-resolving power MS for quantitation and being relatively inexpensive.
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http://dx.doi.org/10.1021/acs.analchem.6b03234DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6010193PMC
November 2016

The central nervous system transcriptome of the weakly electric brown ghost knifefish (Apteronotus leptorhynchus): de novo assembly, annotation, and proteomics validation.

BMC Genomics 2015 Mar 11;16:166. Epub 2015 Mar 11.

Barnett Institute, Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, 412 TF, Boston, MA, 02115, USA.

Background: The brown ghost knifefish (Apteronotus leptorhynchus) is a weakly electric teleost fish of particular interest as a versatile model system for a variety of research areas in neuroscience and biology. The comprehensive information available on the neurophysiology and neuroanatomy of this organism has enabled significant advances in such areas as the study of the neural basis of behavior, the development of adult-born neurons in the central nervous system and their involvement in the regeneration of nervous tissue, as well as brain aging and senescence. Despite substantial scientific interest in this species, no genomic resources are currently available.

Results: Here, we report the de novo assembly and annotation of the A. leptorhynchus transcriptome. After evaluating several trimming and transcript reconstruction strategies, de novo assembly using Trinity uncovered 42,459 unique contigs containing at least a partial protein-coding sequence based on alignment to a reference set of known Actinopterygii sequences. As many as 11,847 of these contigs contained full or near-full length protein sequences, providing broad coverage of the proteome. A variety of non-coding RNA sequences were also identified and annotated, including conserved long intergenic non-coding RNA and other long non-coding RNA observed previously to be expressed in adult zebrafish (Danio rerio) brain, as well as a variety of miRNA, snRNA, and snoRNA. Shotgun proteomics confirmed translation of open reading frames from over 2,000 transcripts, including alternative splice variants. Assignment of tandem mass spectra was greatly improved by use of the assembly compared to databases of sequences from closely related organisms. The assembly and raw reads have been deposited at DDBJ/EMBL/GenBank under the accession number GBKR00000000. Tandem mass spectrometry data is available via ProteomeXchange with identifier PXD001285.

Conclusions: Presented here is the first release of an annotated de novo transcriptome assembly from Apteronotus leptorhynchus, providing a broad overview of RNA expressed in central nervous system tissue. The assembly, which includes substantial coverage of a wide variety of both protein coding and non-coding transcripts, will allow the development of better tools to understand the mechanisms underlying unique characteristics of the knifefish model system, such as their tremendous regenerative capacity and negligible brain senescence.
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http://dx.doi.org/10.1186/s12864-015-1354-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4424500PMC
March 2015

QUDeX-MS: hydrogen/deuterium exchange calculation for mass spectra with resolved isotopic fine structure.

BMC Bioinformatics 2014 Dec 11;15:403. Epub 2014 Dec 11.

Departments of Chemistry and Chemical Biology and Pharmaceutical Sciences and Barnett Institute of Chemical and Biological Analysis, Northeastern University, 360 Huntington Avenue, Boston, MA, 02115, USA.

Background: Hydrogen/deuterium exchange (HDX) coupled to mass spectrometry permits analysis of structure, dynamics, and molecular interactions of proteins. HDX mass spectrometry is confounded by deuterium exchange-associated peaks overlapping with peaks of heavy, natural abundance isotopes, such as carbon-13. Recent studies demonstrated that high-performance mass spectrometers could resolve isotopic fine structure and eliminate this peak overlap, allowing direct detection and quantification of deuterium incorporation.

Results: Here, we present a graphical tool that allows for a rapid and automated estimation of deuterium incorporation from a spectrum with isotopic fine structure. Given a peptide sequence (or elemental formula) and charge state, the mass-to-charge ratios of deuterium-associated peaks of the specified ion is determined. Intensities of peaks in an experimental mass spectrum within bins corresponding to these values are used to determine the distribution of deuterium incorporated. A theoretical spectrum can then be calculated based on the estimated distribution of deuterium exchange to confirm interpretation of the spectrum. Deuterium incorporation can also be detected for ion signals without a priori specification of an elemental formula, permitting detection of exchange in complex samples of unidentified material such as natural organic matter. A tool is also incorporated into QUDeX-MS to help in assigning ion signals from peptides arising from enzymatic digestion of proteins. MATLAB-deployable and standalone versions are available for academic use at qudex-ms.sourceforge.net and agarlabs.com .

Conclusion: Isotopic fine structure HDX-MS offers the potential to increase sequence coverage of proteins being analyzed through mass accuracy and deconvolution of overlapping ion signals. As previously demonstrated, however, the data analysis workflow for HDX-MS data with resolved isotopic fine structure is distinct. QUDeX-MS we hope will aid in the adoption of isotopic fine structure HDX-MS by providing an intuitive workflow and interface for data analysis.
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http://dx.doi.org/10.1186/s12859-014-0403-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4274694PMC
December 2014

Artifacts to avoid while taking advantage of top-down mass spectrometry based detection of protein S-thiolation.

Proteomics 2014 May 17;14(10):1152-7. Epub 2014 Apr 17.

Department of Chemistry and Chemical Biology, Barnett Institute, Northeastern University, Boston, MA, USA; Department of Pharmaceutical Sciences, Northeastern University, Boston, MA, USA; Department of Biochemistry, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA, USA; Department of Chemistry, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA, USA.

Bottom-up MS studies typically employ a reduction and alkylation step that eliminates a class of PTM, S-thiolation. Given that molecular oxygen can mediate S-thiolation from reduced thiols, which are abundant in the reducing intracellular milieu, we investigated the possibility that some S-thiolation modifications are artifacts of protein preparation. Cu/Zn-superoxide dismutase (SOD1) was chosen for this case study as it has a reactive surface cysteine residue, which is readily cysteinylated in vitro. The ability of oxygen to generate S-thiolation artifacts was tested by comparing purification of SOD1 from postmortem human cerebral cortex under aerobic and anaerobic conditions. S-thiolation was ∼50% higher in aerobically processed preparations, consistent with oxygen-dependent artifactual S-thiolation. The ability of endogenous small molecule disulfides (e.g. cystine) to participate in artifactual S-thiolation was tested by blocking reactive protein cysteine residues during anaerobic homogenization. A 50-fold reduction in S-thiolation occurred indicating that the majority of S-thiolation observed aerobically was artifact. Tissue-specific artifacts were explored by comparing brain- and blood-derived protein, with remarkably more artifacts observed in brain-derived SOD1. Given the potential for such artifacts, rules of thumb for sample preparation are provided. This study demonstrates that without taking extraordinary precaution, artifactual S-thiolation of highly reactive, surface-exposed, cysteine residues can result.
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http://dx.doi.org/10.1002/pmic.201300450DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4507715PMC
May 2014

A rapid MALDI-TOF mass spectrometry workflow for Drosophila melanogaster differential neuropeptidomics.

Mol Brain 2013 Dec 27;6:60. Epub 2013 Dec 27.

Depts of Chemistry and Chemical Biology and Pharmaceutical Sciences and Barnett Institute of Chemical and Biological Analysis, Northeastern University, 140 The Fenway, Boston, MA 02115, USA.

Background: Neuropeptides are a diverse category of signaling molecules in the nervous system regulating a variety of processes including food intake, social behavior, circadian rhythms, learning, and memory. Both the identification and functional characterization of specific neuropeptides are ongoing fields of research. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis of nervous tissues from a variety of organisms allows direct detection and identification of neuropeptides. Here, we demonstrate an analysis workflow that allows for the detection of differences in specific neuropeptides amongst a variety of neuropeptides being simultaneously measured. For sample preparation, we describe a straight-forward and rapid (minutes) method where individual adult Drosophila melanogaster brains are analyzed. Using a MATLAB-based data analysis workflow, also compatible with MALDI-TOF mass spectra obtained from other sample preparations and instrumentation, we demonstrate how changes in neuropeptides levels can be detected with this method.

Results: Over fifty isotopically resolved ion signals in the peptide mass range are reproducibly observed across experiments. MALDI-TOF MS profile spectra were used to statistically identify distinct relative differences in organ-wide endogenous levels of detected neuropeptides between biological conditions. In particular, three distinct levels of a particular neuropeptide, pigment dispersing factor, were detected by comparing groups of preprocessed spectra obtained from individual brains across three different D. melanogaster strains, each of which express different amounts of this neuropeptide. Using the same sample preparation, MALDI-TOF/TOF tandem mass spectrometry confirmed that at least 14 ion signals observed across experiments are indeed neuropeptides. Among the identified neuropeptides were three products of the neuropeptide-like precursor 1 gene previously not identified in the literature.

Conclusions: Using MALDI-TOF MS and preprocessing/statistical analysis, changes in relative levels of a particular neuropeptide in D. melanogaster tissue can be statistically detected amongst a variety of neuropeptides. While the data analysis methods should be compatible with other sample preparations, the presented sample preparation method was sufficient to identify previously unconfirmed D. melanogaster neuropeptides.
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http://dx.doi.org/10.1186/1756-6606-6-60DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4022047PMC
December 2013

Resolving isotopic fine structure to detect and quantify natural abundance- and hydrogen/deuterium exchange-derived isotopomers.

Anal Chem 2014 Jan 20;86(1):820-5. Epub 2013 Dec 20.

Department of Chemistry, Brandeis University , Waltham, Massachusetts 02453, United States.

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) is used for analyzing protein dynamics, protein folding/unfolding, and molecular interactions. Until this study, HDX MS experiments employed mass spectral resolving powers that afforded only one peak per nominal mass in a given peptide's isotope distribution, and HDX MS data analysis methods were developed accordingly. A level of complexity that is inherent to HDX MS remained unaddressed, namely, various combinations of natural abundance heavy isotopes and exchanged deuterium shared the same nominal mass and overlapped at previous resolving powers. For example, an A + 2 peak is comprised of (among other isotopomers) a two-(2)H-exchanged/zero-(13)C isotopomer, a one-(2)H-exchanged/one-(13)C isotopomer, and a zero-(2)H-exchanged/two-(13)C isotopomer. Notably, such isotopomers differ slightly in mass as a result of the ∼3 mDa mass defect between (2)H and (13)C atoms. Previous HDX MS methods did not resolve these isotopomers, requiring a natural-abundance-only (before HDX or "time zero") spectrum and data processing to remove its contribution. It is demonstrated here that high-resolution mass spectrometry can be used to detect isotopic fine structure, such as in the A + 2 profile example above, deconvolving the isotopomer species resulting from deuterium incorporation. Resolving isotopic fine structure during HDX MS therefore permits direct monitoring of HDX, which can be calculated as the sum of the fractional peak magnitudes of the deuterium-exchanged isotopomers. This obviates both the need for a time zero spectrum as well as data processing to account for natural abundance heavy isotopes, saving instrument and analysis time.
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http://dx.doi.org/10.1021/ac403365gDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4267757PMC
January 2014

Molecular imaging of drug transit through the blood-brain barrier with MALDI mass spectrometry imaging.

Sci Rep 2013 Oct 4;3:2859. Epub 2013 Oct 4.

Department of Neurosurgery, Brigham and Women's Hospital, Harvard Medical School, Boston MA.

Drug transit through the blood-brain barrier (BBB) is essential for therapeutic responses in malignant glioma. Conventional methods for assessment of BBB penetrance require synthesis of isotopically labeled drug derivatives. Here, we report a new methodology using matrix assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) to visualize drug penetration in brain tissue without molecular labeling. In studies summarized here, we first validate heme as a simple and robust MALDI MSI marker for the lumen of blood vessels in the brain. We go on to provide three examples of how MALDI MSI can provide chemical and biological insights into BBB penetrance and metabolism of small molecule signal transduction inhibitors in the brain - insights that would be difficult or impossible to extract by use of radiolabeled compounds.
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http://dx.doi.org/10.1038/srep02859DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3790202PMC
October 2013

Post-translational modification by cysteine protects Cu/Zn-superoxide dismutase from oxidative damage.

Biochemistry 2013 Sep 26;52(36):6137-44. Epub 2013 Aug 26.

Departments of Biochemistry and Chemistry and Rosenstiel Basic Medical Sciences Research Center, Brandeis University , Waltham, Massachusetts 02454, United States.

Reactive oxygen species (ROS) are cytotoxic. To remove ROS, cells have developed ROS-specific defense mechanisms, including the enzyme Cu/Zn superoxide dismutase (SOD1), which catalyzes the disproportionation of superoxide anions into molecular oxygen and hydrogen peroxide. Although hydrogen peroxide is less reactive than superoxide, it is still capable of oxidizing, unfolding, and inactivating SOD1, at least in vitro. To explore the relevance of post-translational modification (PTM) of SOD1, including peroxide-related modifications, SOD1 was purified from postmortem human nervous tissue. As much as half of all purified SOD1 protein contained non-native post-translational modifications (PTMs), the most prevalent modifications being cysteinylation and peroxide-related oxidations. Many PTMs targeted a single reactive SOD1 cysteine, Cys111. An intriguing observation was that unlike native SOD1, cysteinylated SOD1 was not oxidized. To further characterize how cysteinylation may protect SOD1 from oxidation, cysteine-modified SOD1 was prepared in vitro and exposed to peroxide. Cysteinylation conferred nearly complete protection from peroxide-induced oxidation of SOD1. Moreover, SOD1 that has been cysteinylated and peroxide oxidized in vitro comprised a set of PTMs that bear a striking resemblance to the myriad of PTMs observed in SOD1 purified from human tissue.
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http://dx.doi.org/10.1021/bi4006122DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3859700PMC
September 2013

Structural consequences of cysteinylation of Cu/Zn-superoxide dismutase.

Biochemistry 2013 Sep 26;52(36):6145-50. Epub 2013 Aug 26.

Departments of Biochemistry and Chemistry and Rosenstiel Basic Medical Sciences Research Center, Brandeis University , Waltham, Massachusetts 02454, United States.

The metalloenzyme Cu/Zn-superoxide dismutase (SOD1) catalyzes the reduction of superoxide anions into molecular oxygen and hydrogen peroxide. Hydrogen peroxide can oxidize SOD1, resulting in aberrant protein conformational changes, disruption of SOD1 function, and DNA damage. Cells may have evolved mechanisms of regulation that prevent such oxidation. We observed that cysteinylation of cysteine 111 (Cys111) of SOD1 prevents oxidation by peroxide (DOI 10.1021/bi4006122 ). In this article, we characterize cysteinylated SOD1 using differential scanning fluorometry and X-ray crystallography. The stoichiometry of binding was one cysteine per SOD1 dimer, and there does not appear to be free volume for a second cysteine without disrupting the dimer interface. Much of the three-dimensional structure of SOD1 is unaffected by cysteinylation. However, local conformational changes are observed in the cysteinylated monomer that include changes in conformation of the electrostatic loop (loop VII; residues 133-144) and the dimer interface (loop VI; residues 102-115). In addition, our data shows how cysteinylation precludes oxidation of cysteine 111 and suggests possible cross-talk between the dimer interface and the electrostatic loop.
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http://dx.doi.org/10.1021/bi400613hDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3859770PMC
September 2013

Performance comparisons of nano-LC systems, electrospray sources and LC-MS-MS platforms.

J Chromatogr Sci 2014 Feb 17;52(2):120-7. Epub 2013 Jan 17.

1Department of Chemistry.

Selecting a suitable nano-liquid chromatography system (LC), ionization source and mass spectrometer for LC-tandem mass spectrometry (MS-MS) studies is complicated by numerous competing technologies. This study compares four popular nano-LC systems, four ionization sources and three MS facilities that use completely different LC-MS-MS systems. Statistically significant differences in LC performance were identified with similarly performing Proxeon, Waters and Eksigent nanoLC-Ultra systems [retention time routinely at 0.7-0.9% relative standard deviation (RSD)], and all outperformed the Eksigent nanoLC-2D (RSD ∼2%). In addition, compatibility issues were identified between the Bruker HCT ion trap mass spectrometer and both the Eksigent nanoLC-2D and the Bruker nanoelectrospray source. The electrospray source itself had an unexpected and striking effect on chromatographic reproducibility on the Bruker HCT ion trap. The New Objective nanospray source significantly outperformed the Bruker nanospray source in retention time RSD (1% RSD versus 14% RSD, respectively); and the Bruker nebulized nanospray source outperformed both of these traditional, non-nebulized sources (0.5% RSD in retention time). Finally, to provide useful benchmarks for overall proteomics sensitivity, different LC-MS-MS platforms were compared by analyzing a range of concentrations of tryptic digests of bovine serum albumin at three MS facilities. The results indicate that similar sensitivity can be realized with a Bruker HCT-Ultra ion trap, a Thermo LTQ-Velos Linear ion trap and a Thermo LTQ-Orbitrap XL-ETD.
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http://dx.doi.org/10.1093/chromsci/bms255DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3886563PMC
February 2014