Publications by authors named "Thomas J D Jørgensen"

72 Publications

The intrinsic instability of the hydrolase domain of lipoprotein lipase facilitates its inactivation by ANGPTL4-catalyzed unfolding.

Proc Natl Acad Sci U S A 2021 Mar;118(12)

Finsen Laboratory, Rigshospitalet, DK-2200 Copenhagen N, Denmark;

The complex between lipoprotein lipase (LPL) and its endothelial receptor (GPIHBP1) is responsible for the lipolytic processing of triglyceride-rich lipoproteins (TRLs) along the capillary lumen, a physiologic process that releases lipid nutrients for vital organs such as heart and skeletal muscle. LPL activity is regulated in a tissue-specific manner by endogenous inhibitors (angiopoietin-like [ANGPTL] proteins 3, 4, and 8), but the molecular mechanisms are incompletely understood. ANGPTL4 catalyzes the inactivation of LPL monomers by triggering the irreversible unfolding of LPL's α/β-hydrolase domain. Here, we show that this unfolding is initiated by the binding of ANGPTL4 to sequences near LPL's catalytic site, including β2, β3-α3, and the lid. Using pulse-labeling hydrogen‒deuterium exchange mass spectrometry, we found that ANGPTL4 binding initiates conformational changes that are nucleated on β3-α3 and progress to β5 and β4-α4, ultimately leading to the irreversible unfolding of regions that form LPL's catalytic pocket. LPL unfolding is context dependent and varies with the thermal stability of LPL's α/β-hydrolase domain ( of 34.8 °C). GPIHBP1 binding dramatically increases LPL stability ( of 57.6 °C), while ANGPTL4 lowers the onset of LPL unfolding by ∼20 °C, both for LPL and LPL•GPIHBP1 complexes. These observations explain why the binding of GPIHBP1 to LPL retards the kinetics of ANGPTL4-mediated LPL inactivation at 37 °C but does not fully suppress inactivation. The allosteric mechanism by which ANGPTL4 catalyzes the irreversible unfolding and inactivation of LPL is an unprecedented pathway for regulating intravascular lipid metabolism.
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http://dx.doi.org/10.1073/pnas.2026650118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8000434PMC
March 2021

Probing the Conformational Dynamics of Affinity-Enhanced T Cell Receptor Variants upon Binding the Peptide-Bound Major Histocompatibility Complex by Hydrogen/Deuterium Exchange Mass Spectrometry.

Biochemistry 2021 Mar 9;60(11):859-872. Epub 2021 Mar 9.

Department of Pharmacy, University of Copenhagen, 2100 Copenhagen, Denmark.

Binding of the T cell receptor (TCR) to its cognate, peptide antigen-loaded major histocompatibility complex (pMHC) is a key interaction for triggering T cell activation and ultimately elimination of the target cell. Despite the importance of this interaction for cellular immunity, a comprehensive molecular understanding of TCR specificity and affinity is lacking. We conducted hydrogen/deuterium exchange mass spectrometry (HDX-MS) analyses of individual affinity-enhanced TCR variants and clinically relevant pMHC class I molecules (HLA-A*0201/NY-ESO-1) to investigate the causality between increased binding affinity and conformational dynamics in TCR-pMHC complexes. Differential HDX-MS analyses of TCR variants revealed that mutations for affinity enhancement in TCR CDRs altered the conformational response of TCR to pMHC ligation. Improved pMHC binding affinity was in general observed to correlate with greater differences in HDX upon pMHC binding in modified TCR CDR loops, thereby providing new insights into the TCR-pMHC interaction. Furthermore, a specific point mutation in the β-CDR3 loop of the NY-ESO-1 TCR associated with a substantial increase in binding affinity resulted in a substantial change in pMHC binding kinetics (i.e., very slow , revealed by the detection of EX1 HDX kinetics), thus providing experimental evidence for a slow induced-fit binding mode. We also examined the conformational impact of pMHC binding on an unrelated TRAV12-2 gene-encoded TCR directed against the immunodominant MART-1 cancer antigen restricted by HLA-A*0201. Our findings provide a molecular basis for the observed TRAV12-2 gene bias in natural CD8 T cell-based immune responses against the MART-1 antigen, with potential implications for general ligand discrimination and TCR cross-reactivity processes.
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http://dx.doi.org/10.1021/acs.biochem.1c00035DOI Listing
March 2021

Ultraviolet Photodissociation of Protonated Peptides and Proteins Can Proceed with H/D Scrambling.

Anal Chem 2021 01 9;93(2):691-696. Epub 2020 Dec 9.

Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M 5230, Denmark.

Ultraviolet photodissociation (UVPD) has recently been introduced as an ion activation method for the determination of single-residue deuterium levels in H/D exchange tandem mass spectrometry experiments. In this regard, it is crucial to know which fragment ion types can be utilized for this purpose. UVPD yields rich product ion spectra where all possible backbone fragment ion types (a/x, b/y, and c/z) are typically observed. Here we provide a detailed investigation of the level of H/D scrambling for all fragment ion types upon UVPD of the peptide scrambling probe P1 (HHHHHHIIKIIK) using an Orbitrap tribrid mass spectrometer equipped with a solid-state 213 nm UV laser. The most abundant UVPD-generated fragment ions (i.e., b/y ions) exhibit extensive H/D scrambling. Similarly, a/x and c/z ions have also undergone H/D scrambling due to UV-induced heating of the precursor ion population. Therefore, dominant b/y ions upon UVPD of protonated peptides are a strong indicator for the occurrence of extensive H/D scrambling of the precursor ion population. In contrast to peptide P1, UV-irradiation of ubiquitin did not induce H/D scrambling in the nonfragmented precursor ion population. However, the UVPD-generated b and a ions from ubiquitin exhibit extensive H/D scrambling. To minimize H/D scrambling, short UV-irradiation time and high gas pressures are recommended.
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http://dx.doi.org/10.1021/acs.analchem.0c02957DOI Listing
January 2021

Deglycosylation by the Acidic Glycosidase PNGase H Enables Analysis of N-Linked Glycoproteins by Hydrogen/Deuterium Exchange Mass Spectrometry.

J Am Soc Mass Spectrom 2020 Nov 5;31(11):2305-2312. Epub 2020 Oct 5.

Department of Pharmacy, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark.

Hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS) has become an important method to study the structural dynamics of proteins. However, glycoproteins represent a challenge to the traditional HDX-MS workflow for determining the deuterium uptake of the protein segments that contain the glycan. We have recently demonstrated the utility of the glycosidase PNGase A to enable HDX-MS analysis of N-glycosylated protein regions. Here, we have investigated the use of the acidic glycosidase PNGase H, which has a pH optimum at 2.6, to efficiently deglycosylate N-linked glycosylated peptides during HDX-MS analysis of glycoproteins. Our results show that PNGase H retains high deglycosylation activity at HDX quench conditions. When used in an HDX-MS workflow, PNGase H allowed the extraction of HDX data from all five glycosylated regions of the serpin α-antichymotrypsin. We demonstrate that PNGase A and PNGase H are capable of similar deglycosylation performance during HDX-MS analysis of α-antichymotrypsin and the IgG1 antibody trastuzumab (TZ). However, PNGase H provides broader specificity and greater tolerance to the disulfide-bond reducing agent TCEP, while PNGase A offers advantages in terms of commercial availability and purity. Overall, our findings demonstrate the unique features of PNGase H for improving conformational analysis of glycoproteins by HDX-MS, in particular, challenging glycoproteins containing both glycosylations and disulfide bonds.
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http://dx.doi.org/10.1021/jasms.0c00258DOI Listing
November 2020

Avoiding H/D Scrambling with Minimal Ion Transmission Loss for HDX-MS/MS-ETD Analysis on a High-Resolution Q-TOF Mass Spectrometer.

Anal Chem 2020 06 19;92(11):7453-7461. Epub 2020 May 19.

Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M 5230, Denmark.

Hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS) enables the study of protein dynamics by measuring the time-resolved deuterium incorporation into a protein incubated in DO. Using electron-based fragmentation in the gas phase it is possible to measure deuterium uptake at single-residue resolution. However, a prerequisite for this approach is that the solution-phase labeling is conserved in the gas phase prior to precursor fragmentation. It is therefore essential to reduce or even avoid intramolecular hydrogen/deuterium migration, which causes randomization of the deuterium labels along the peptide (hydrogen scrambling). Here, we describe an optimization strategy for reducing scrambling to a negligible level while minimizing the impact on sensitivity on a high-resolution Q-TOF equipped with ETD and an electrospray ionization interface consisting of a glass transfer capillary followed by a dual ion funnel. In our strategy we narrowed down the optimization to two accelerating potentials, and we defined the optimization of these in a simple rule by accounting for their interdependency in relation to scrambling and transmission efficiency. Using this rule, we were able to reduce scrambling from 75% to below 5% on average using the highly scrambling-sensitive quadruply charged P1 peptide scrambling probe resulting in a minor 33% transmission loss. To demonstrate the applicability of this approach, we probe the dynamics of certain regions in cytochrome .
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http://dx.doi.org/10.1021/acs.analchem.9b05208DOI Listing
June 2020

Unfolding of monomeric lipoprotein lipase by ANGPTL4: Insight into the regulation of plasma triglyceride metabolism.

Proc Natl Acad Sci U S A 2020 02 7;117(8):4337-4346. Epub 2020 Feb 7.

Finsen Laboratory, Rigshospitalet, DK-2200 Copenhagen N, Denmark;

The binding of lipoprotein lipase (LPL) to GPIHBP1 focuses the intravascular hydrolysis of triglyceride-rich lipoproteins on the surface of capillary endothelial cells. This process provides essential lipid nutrients for vital tissues (e.g., heart, skeletal muscle, and adipose tissue). Deficiencies in either LPL or GPIHBP1 impair triglyceride hydrolysis, resulting in severe hypertriglyceridemia. The activity of LPL in tissues is regulated by angiopoietin-like proteins 3, 4, and 8 (ANGPTL). Dogma has held that these ANGPTLs inactivate LPL by converting LPL homodimers into monomers, rendering them highly susceptible to spontaneous unfolding and loss of enzymatic activity. Here, we show that binding of an LPL-specific monoclonal antibody (5D2) to the tryptophan-rich lipid-binding loop in the carboxyl terminus of LPL prevents homodimer formation and forces LPL into a monomeric state. Of note, 5D2-bound LPL monomers are as stable as LPL homodimers (i.e., they are not more prone to unfolding), but they remain highly susceptible to ANGPTL4-catalyzed unfolding and inactivation. Binding of GPIHBP1 to LPL alone or to 5D2-bound LPL counteracts ANGPTL4-mediated unfolding of LPL. In conclusion, ANGPTL4-mediated inactivation of LPL, accomplished by catalyzing the unfolding of LPL, does not require the conversion of LPL homodimers into monomers. Thus, our findings necessitate changes to long-standing dogma on mechanisms for LPL inactivation by ANGPTL proteins. At the same time, our findings align well with insights into LPL function from the recent crystal structure of the LPL•GPIHBP1 complex.
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http://dx.doi.org/10.1073/pnas.1920202117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7049152PMC
February 2020

Recommendations for performing, interpreting and reporting hydrogen deuterium exchange mass spectrometry (HDX-MS) experiments.

Nat Methods 2019 07 27;16(7):595-602. Epub 2019 Jun 27.

Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA.

Hydrogen deuterium exchange mass spectrometry (HDX-MS) is a powerful biophysical technique being increasingly applied to a wide variety of problems. As the HDX-MS community continues to grow, adoption of best practices in data collection, analysis, presentation and interpretation will greatly enhance the accessibility of this technique to nonspecialists. Here we provide recommendations arising from community discussions emerging out of the first International Conference on Hydrogen-Exchange Mass Spectrometry (IC-HDX; 2017). It is meant to represent both a consensus viewpoint and an opportunity to stimulate further additions and refinements as the field advances.
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http://dx.doi.org/10.1038/s41592-019-0459-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6614034PMC
July 2019

Did evolution create a flexible ligand-binding cavity in the urokinase receptor through deletion of a plesiotypic disulfide bond?

J Biol Chem 2019 05 20;294(18):7403-7418. Epub 2019 Mar 20.

From the Finsen Laboratory, Rigshospitalet, DK-2200 Copenhagen N, Denmark,

The urokinase receptor (uPAR) is a founding member of a small protein family with multiple Ly6/uPAR (LU) domains. The motif defining these LU domains contains five plesiotypic disulfide bonds stabilizing its prototypical three-fingered fold having three protruding loops. Notwithstanding the detailed knowledge on structure-function relationships in uPAR, one puzzling enigma remains unexplored. Why does the first LU domain in uPAR (DI) lack one of its consensus disulfide bonds, when the absence of this particular disulfide bond impairs the correct folding of other single LU domain-containing proteins? Here, using a variety of contemporary biophysical methods, we found that reintroducing the two missing half-cystines in uPAR DI caused the spontaneous formation of the corresponding consensus 7-8 LU domain disulfide bond. Importantly, constraints due to this cross-link impaired (i) the binding of uPAR to its primary ligand urokinase and (ii) the flexible interdomain assembly of the three LU domains in uPAR. We conclude that the evolutionary deletion of this particular disulfide bond in uPAR DI may have enabled the assembly of a high-affinity urokinase-binding cavity involving all three LU domains in uPAR. Of note, an analogous neofunctionalization occurred in snake venom α-neurotoxins upon loss of another pair of the plesiotypic LU domain half-cystines. In summary, elimination of the 7-8 consensus disulfide bond in the first LU domain of uPAR have significant functional and structural consequences.
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http://dx.doi.org/10.1074/jbc.RA119.007847DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6509485PMC
May 2019

A disordered acidic domain in GPIHBP1 harboring a sulfated tyrosine regulates lipoprotein lipase.

Proc Natl Acad Sci U S A 2018 06 13;115(26):E6020-E6029. Epub 2018 Jun 13.

Finsen Laboratory, Rigshospitalet, DK-2200 Copenhagen N, Denmark;

The intravascular processing of triglyceride-rich lipoproteins depends on lipoprotein lipase (LPL) and GPIHBP1, a membrane protein of endothelial cells that binds LPL within the subendothelial spaces and shuttles it to the capillary lumen. In the absence of GPIHBP1, LPL remains mislocalized within the subendothelial spaces, causing severe hypertriglyceridemia (chylomicronemia). The N-terminal domain of GPIHBP1, an intrinsically disordered region (IDR) rich in acidic residues, is important for stabilizing LPL's catalytic domain against spontaneous and ANGPTL4-catalyzed unfolding. Here, we define several important properties of GPIHBP1's IDR. First, a conserved tyrosine in the middle of the IDR is posttranslationally modified by O-sulfation; this modification increases both the affinity of GPIHBP1-LPL interactions and the ability of GPIHBP1 to protect LPL against ANGPTL4-catalyzed unfolding. Second, the acidic IDR of GPIHBP1 increases the probability of a GPIHBP1-LPL encounter via electrostatic steering, increasing the association rate constant () for LPL binding by >250-fold. Third, we show that LPL accumulates near capillary endothelial cells even in the absence of GPIHBP1. In wild-type mice, we expect that the accumulation of LPL in close proximity to capillaries would increase interactions with GPIHBP1. Fourth, we found that GPIHBP1's IDR is not a key factor in the pathogenicity of chylomicronemia in patients with the GPIHBP1 autoimmune syndrome. Finally, based on biophysical studies, we propose that the negatively charged IDR of GPIHBP1 traverses a vast space, facilitating capture of LPL by capillary endothelial cells and simultaneously contributing to GPIHBP1's ability to preserve LPL structure and activity.
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http://dx.doi.org/10.1073/pnas.1806774115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6042107PMC
June 2018

Long-Lived Folding Intermediates Predominate the Targeting-Competent Secretome.

Structure 2018 05 5;26(5):695-707.e5. Epub 2018 Apr 5.

KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, 3000 Leuven, Belgium. Electronic address:

Secretory preproteins carry signal peptides fused amino-terminally to mature domains. They are post-translationally targeted to cross the plasma membrane in non-folded states with the help of translocases, and fold only at their final destinations. The mechanism of this process of postponed folding is unknown, but is generally attributed to signal peptides and chaperones. We herein demonstrate that, during targeting, most mature domains maintain loosely packed folding intermediates. These largely soluble states are signal peptide independent and essential for translocase recognition. These intermediates are promoted by mature domain features: residue composition, elevated disorder, and reduced hydrophobicity. Consequently, a mature domain folds slower than its cytoplasmic structural homolog. Some mature domains could not evolve stable, loose intermediates, and hence depend on signal peptides for slow folding to the detriment of solubility. These unique features of secretory proteins impact our understanding of protein trafficking, folding, and aggregation, and thus place them in a distinct class.
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http://dx.doi.org/10.1016/j.str.2018.03.006DOI Listing
May 2018

Conformational preludes to the latency transition in PAI-1 as determined by atomistic computer simulations and hydrogen/deuterium-exchange mass spectrometry.

Sci Rep 2017 07 26;7(1):6636. Epub 2017 Jul 26.

Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230, Odense, M, Denmark.

Both function and dysfunction of serine protease inhibitors (serpins) involve massive conformational change in their tertiary structure but the dynamics facilitating these events remain poorly understood. We have studied the dynamic preludes to conformational change in the serpin plasminogen activator inhibitor 1 (PAI-1). We report the first multi-microsecond atomistic molecular dynamics simulations of PAI-1 and compare the data with experimental hydrogen/deuterium-exchange data (HDXMS). The simulations reveal notable conformational flexibility of helices D, E and F and major fluctuations are observed in the W86-loop which occasionally leads to progressive detachment of β-strand 2 A from β-strand 3 A. An interesting correlation between C-RMSD values from simulations and experimental HDXMS data is observed. Helices D, E and F are known to be important for the overall stability of active PAI-1 as ligand binding in this region can accelerate or decelerate the conformational inactivation. Plasticity in this region may thus be mechanistically linked to the conformational change, possibly through facilitation of further unfolding of the hydrophobic core, as previously reported. This study provides a promising example of how computer simulations can help tether out mechanisms of serpin function and dysfunction at a spatial and temporal resolution that is far beyond the reach of any experiment.
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http://dx.doi.org/10.1038/s41598-017-06290-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5529462PMC
July 2017

The T-Cell Receptor Can Bind to the Peptide-Bound Major Histocompatibility Complex and Uncomplexed β-Microglobulin through Distinct Binding Sites.

Biochemistry 2017 08 19;56(30):3945-3961. Epub 2017 Jul 19.

Department of Pharmacy, University of Copenhagen , 2100 Copenhagen, Denmark.

T-Cell receptor (TCR)-mediated recognition of the peptide-bound major histocompatibility complex (pMHC) initiates an adaptive immune response against antigen-presenting target cells. The recognition events take place at the TCR-pMHC interface, and their effects on TCR conformation and dynamics are controversial. Here, we have measured the time-resolved hydrogen/deuterium exchange (HDX) of a soluble TCR in the presence and absence of its cognate pMHC by mass spectrometry to delineate the impact of pMHC binding on solution-phase structural dynamics in the TCR. Our results demonstrate that while TCR-pMHC complex formation significantly stabilizes distinct CDR loops of the TCR, it does not trigger structural changes in receptor segments remote from the binding interface. Intriguingly, our HDX measurements reveal that the TCR α-constant domain (C- and F-strand) directly interacts with the unbound MHC light chain, β-microglobulin (βm). Surface plasmon resonance measurements corroborated a binding event between TCR and βm with a dissociation constant of 167 ± 20 μM. We propose a model structure for the TCR-βm complex based on a refined protein-protein docking approach driven by HDX data and information from molecular dynamics simulations. Using a biological assay based on TCR gene-engineered primary human T cells, we did not observe a significant effect of βm on T-cell cytotoxicity, suggesting an alternate role for βm binding. Overall, we show that binding of βm to the TCR occurs in vitro and, as such, not only should be considered in structure-function studies of the TCR-pMHC complex but also could play a hitherto unidentified role in T-cell function in vivo.
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http://dx.doi.org/10.1021/acs.biochem.7b00385DOI Listing
August 2017

Uranyl Photocleavage of Phosphopeptides Yields Truncated C-Terminally Amidated Peptide Products.

Chembiochem 2017 06 23;18(12):1117-1122. Epub 2017 May 23.

Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark.

The uranyl ion (UO ) binds phosphopeptides with high affinity, and when irradiated with UV-light, it can cleave the peptide backbone. In this study, high-accuracy tandem mass spectrometry and enzymatic assays were used to characterise the photocleavage products resulting from the uranyl photocleavage reaction of a tetraphosphorylated β-casein model peptide. We show that the primary photocleavage products of the uranyl-catalysed reaction are C-terminally amidated. This could be of great interest to the pharmaceutical industry, as efficient peptide amidation reactions are one of the top challenges in green pharmaceutical chemistry.
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http://dx.doi.org/10.1002/cbic.201700103DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5488209PMC
June 2017

Removal of N-Linked Glycosylations at Acidic pH by PNGase A Facilitates Hydrogen/Deuterium Exchange Mass Spectrometry Analysis of N-Linked Glycoproteins.

Anal Chem 2016 12 28;88(24):12479-12488. Epub 2016 Nov 28.

Department of Pharmacy, University of Copenhagen , Universitetsparken 2, 2100 Copenhagen, Denmark.

Protein glycosylation is the most frequent post-translational modification and is present on more than 50% of eukaryotic proteins. Glycosylation covers a wide subset of modifications involving many types of complex oligosaccharide structures, making structural analysis of glycoproteins and their glycans challenging for most analytical techniques. Hydrogen/deuterium exchange monitored by mass spectrometry is a sensitive technique for investigation of protein conformational dynamics of complex heterogeneous proteins in solution. N-linked glycoproteins however pose a challenge for HDX-MS. HDX information can typically not be obtained from regions of the glycoprotein that contain the actual N-linked glycan as glycan heterogeneity combined with pepsin digestion yields a large diversity of peptic N-glycosylated peptides that can be difficult to detect. Here, we present a novel HDX-MS workflow for analysis of the conformational dynamics of N-linked glycoproteins that utilizes the enzyme PNGase A for deglycosylation of labeled peptic N-linked glycopeptides at HDX quench conditions, i.e., acidic pH and low temperature. PNGase A-based deglycosylation is thus performed after labeling (post-HDX) and the utility of this approach is demonstrated during analysis of the monoclonal antibody Trastuzumab for which it has been shown that the native conformational dynamics is dependent on the N-linked glycan. In summary, the HDX-MS workflow with integrated PNGase A deglycosylation enables analysis of the native HDX of protein regions containing N-linked glycan sites and should thus significantly improve our ability to study the conformational properties of glycoproteins.
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http://dx.doi.org/10.1021/acs.analchem.6b03951DOI Listing
December 2016

Epitope-dependent Functional Effects of Celiac Disease Autoantibodies on Transglutaminase 2.

J Biol Chem 2016 Dec 26;291(49):25542-25552. Epub 2016 Oct 26.

From the Centre for Immune Regulation and Department of Immunology, University of Oslo and Oslo University Hospital, N-0372 Oslo, Norway and.

Transglutaminase 2 (TG2) is a Ca-dependent cross-linking enzyme involved in the pathogenesis of CD. We have previously characterized a panel of anti-TG2 mAbs generated from gut plasma cells of celiac patients and identified four epitopes (epitopes 1-4) located in the N-terminal part of TG2. Binding of the mAbs induced allosteric changes in TG2. Thus, we aimed to determine whether these mAbs could influence enzymatic activity through modulation of TG2 susceptibility to oxidative inactivation and Ca affinity. All tested epitope 1 mAbs, as well as 679-14-D04, which recognizes a previously uncharacterized epitope, prevented oxidative inactivation and increased Ca sensitivity of TG2. We have identified crucial residues for binding of 679-14-D04 located within a Ca binding site. Epitope 1 mAbs and 679-14-D04, although recognizing separate epitopes, behaved similarly when assessing their effect on TG2 conformation, suggesting that the shared effects on TG2 function can be explained by induction of the same conformational changes. None of the mAbs targeting other epitopes showed these effects, but epitope 2 mAbs reduced the rate of TG2-catalyzed reactions. Collectively, these effects could be relevant to the pathogenesis of CD. In A20 B cells transduced with TG2-specific B-cell receptor, epitope 2-expressing cells had poorer uptake of TG2-gluten complexes and were less efficient in gluten epitope presentation to T cells than cells expressing an epitope 1 receptor. Thus, the ability of epitope 1-targeting B cells to keep TG2 active and protected from oxidation might explain why generation of epitope 1-targeting plasma cells seems to be favored in celiac patients.
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http://dx.doi.org/10.1074/jbc.M116.738161DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5207253PMC
December 2016

An Asymmetric Runaway Domain Swap Antithrombin Dimer as a Key Intermediate for Polymerization Revealed by Hydrogen/Deuterium-Exchange Mass Spectrometry.

Anal Chem 2017 01 15;89(1):616-624. Epub 2016 Dec 15.

Department of Biochemistry and Molecular Biology, University of Southern Denmark , Campusvej 55, 5230 Odense M, Denmark.

Antithrombin deficiency is associated with increased risk of venous thrombosis. In certain families, this condition is caused by pathogenic polymerization of mutated antithrombin in the blood. To facilitate future development of pharmaceuticals against antithrombin polymerization, an improved understanding of the polymerogenic intermediates is crucial. However, X-ray crystallography of these intermediates is severely hampered by the difficulty in obtaining well-diffracting crystals of transient and heterogeneous noncovalent protein assemblies. Furthermore, their large size prohibits structural analysis by NMR spectroscopy. Here, we show how hydrogen/deuterium-exchange mass spectrometry (HDX-MS) provides detailed insight into the structural dynamics of each subunit in a polymerization-competent antithrombin dimer. Upon deuteration, this dimer surprisingly yields bimodal isotope distributions for the majority of peptides, demonstrating an asymmetric configuration of the two subunits. The data reveal that one subunit is very dynamic, potentially intrinsically disordered, whereas the other is considerably less dynamic. The local subunit-specific deuterium uptake of this polymerization-competent dimer strongly supports a β4A-β5A β-hairpin runaway domain swap mechanism for antithrombin polymerization. HDX-MS thus holds exceptional promise as an enabling analytical technique in the efforts toward future pharmacological intervention with protein polymerization and associated diseases.
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http://dx.doi.org/10.1021/acs.analchem.6b02518DOI Listing
January 2017

Copper(II) Ions Increase Plasminogen Activator Inhibitor Type 1 Dynamics in Key Structural Regions That Govern Stability.

Biochemistry 2016 08 27;55(31):4386-98. Epub 2016 Jul 27.

Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee , Walters Life Sciences Building, 1414 Cumberland Avenue, Knoxville, Tennessee 37996, United States.

Plasminogen activator inhibitor type 1 (PAI-1) regulates the fibrinolysis pathway by inhibiting the protease activity of plasminogen activators. PAI-1 works in concert with vitronectin (VN), an extracellular protein that aids in localization of active PAI-1 to tissues. The Peterson laboratory demonstrated that Cu(II) and other transition metals modulate the stability of PAI-1, exhibiting effects that are dependent on the presence or absence of the somatomedin B (SMB) domain of VN. The study presented here dissects the changes in molecular dynamics underlying the destabilizing effects of Cu(II) on PAI-1. We utilize backbone amide hydrogen/deuterium exchange monitored by mass spectrometry to assess PAI-1 dynamics in the presence and absence of Cu(II) ions with and without the SMB domain of VN. We show that Cu(II) produces an increase in dynamics in regions important for the function and overall stability of PAI-1, while the SMB domain elicits virtually the opposite effect. A mutant form of PAI-1 lacking two N-terminal histidine residues at positions 2 and 3 exhibits similar increases in dynamics upon Cu(II) binding compared to that of active wild-type PAI-1, indicating that the observed structural effects are not a result of coordination of Cu(II) to these histidine residues. Finally, addition of Cu(II) results in an acceleration of the local unfolding kinetics of PAI-1 presumed to be on pathway to the latency conversion. The effect of ligands on the dynamics of PAI-1 adds another intriguing dimension to the mechanisms for regulation of PAI-1 stability and function.
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http://dx.doi.org/10.1021/acs.biochem.6b00256DOI Listing
August 2016

Dissecting the interaction between transglutaminase 2 and fibronectin.

Amino Acids 2017 03 9;49(3):489-500. Epub 2016 Jul 9.

Centre for Immune Regulation and Department of Immunology, University of Oslo, Oslo University Hospital, Oslo, Norway.

In the extracellular environment, the enzyme transglutaminase 2 (TG2) is involved in cell-matrix interactions through association with the extracellular matrix protein, fibronectin (FN). The 45 kDa gelatin-binding domain of FN (45FN) is responsible for the binding to TG2. Previous studies have demonstrated that the FN-binding site of TG2 is located in the N-terminal domain of the enzyme although with conflicting results regarding the specific residues involved. Here we have mapped the FN interaction site of human TG2 by use of hydrogen/deuterium exchange coupled with mass spectrometry, and we confirm that the FN-binding site is located in the N-terminal domain of TG2. Furthermore, by combination of site-directed mutagenesis and surface plasmon resonance analysis we have identified the TG2 residues K30, R116 and H134 as crucial to maintain the high affinity interaction with FN. Mutation of all three residues simultaneously reduced binding to 45FN by more than 2000-fold. We also identified residues in the catalytic core domain of TG2 that contributed to FN binding, hence extending the binding interface between TG2 and FN. This study provides new insights into the high affinity interaction between TG2 and FN.
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http://dx.doi.org/10.1007/s00726-016-2296-yDOI Listing
March 2017

An RNA Aptamer Inhibits a Mutation-Induced Inactivating Misfolding of a Serpin.

Cell Chem Biol 2016 06 2;23(6):700-8. Epub 2016 Jun 2.

Department of Molecular Biology and Genetics, Aarhus University, 8000 Aarhus, Denmark. Electronic address:

Most serpins are fast and specific inhibitors of extracellular serine proteases controlling biological processes such as blood coagulation, fibrinolysis, tissue remodeling, and inflammation. The inhibitory activity of serpins is based on a conserved metastable structure and their conversion to a more stable state during reaction with the target protease. However, the metastable state also makes serpins vulnerable to mutations, resulting in disease caused by inactive and misfolded monomeric or polymeric forms ("serpinopathy"). Misfolding can occur either intracellularly (type-I serpinopathies) or extracellularly (type-II serpinopathies). We have isolated a 2'-fluoropyrimidine-modified RNA aptamer, which inhibits a mutation-induced inactivating misfolding of the serpin α1-antichymotrypsin. It is the first agent able to stabilize a type-II mutation of a serpin without interfering with the inhibitory mechanism, thereby presenting a solution for the long-standing challenge of preventing pathogenic misfolding without compromising the inhibitory function.
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http://dx.doi.org/10.1016/j.chembiol.2016.04.013DOI Listing
June 2016

Conformational analysis of large and highly disulfide-stabilized proteins by integrating online electrochemical reduction into an optimized H/D exchange mass spectrometry workflow.

Anal Chem 2015 Sep 18;87(17):8880-8. Epub 2015 Aug 18.

Department of Pharmacy, University of Copenhagen , Universitetsparken 2, Copenhagen E, DK-2100, Denmark.

Analysis of disulfide-bonded proteins by hydrogen/deuterium exchange mass spectrometry (HDX-MS) requires effective and rapid reduction of disulfide bonds before enzymatic digestion in order to increase sequence coverage. In a conventional HDX-MS workflow, disulfide bonds are reduced chemically by addition of a reducing agent to the quench solution (e.g., tris(2-carboxyethyl)phosphine (TCEP)). The chemical reduction, however, is severely limited under quenched conditions due to a narrow time window as well as low pH and temperature. Here, we demonstrate the real-world applicability of integrating electrochemical reduction into an online HDX-MS workflow. We have optimized the electrochemical reduction efficiency during HDX-MS analysis of two particularly challenging disulfide stabilized proteins: a therapeutic IgG1-antibody and nerve growth factor-β (NGF). Several different parameters (flow rate and applied square wave potential, as well as the type of labeling and quench buffer) were investigated, and the optimized workflow increased the sequence coverage of NGF from 46% with chemical reduction to 99%, when electrochemical reduction was applied. Additionally, the optimized workflow also enabled a similar high sequence coverage of 96% and 87% for the heavy and light chain of the IgG1-antibody, respectively. The presented results demonstrate the successful electrochemical reduction during HDX-MS analysis of both a small exceptional tightly disulfide-bonded protein (NGF) as well as the largest protein attempted to date (IgG1-antibody). We envision that online electrochemical reduction is poised to decrease the complexity of sample handling and increase the versatility of the HDX-MS technique.
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http://dx.doi.org/10.1021/acs.analchem.5b01996DOI Listing
September 2015

Effect of Metals in Biomimetic Dimetal Complexes on Affinity and Gas-Phase Protection of Phosphate Esters.

Anal Chem 2015 Jul 26;87(14):7060-8. Epub 2015 Jun 26.

†Department of Biochemistry and Molecular Biology, and ‡Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, 5230, Odense M, Denmark.

Although the biomimetic dimetal complex [LGa2(OH)2(H2O)2](3+) [L = 2,6-bis((N,N'-bis(2-picolyl)amino)methyl)-4-tertbutylphenolate] provides efficient protection against phosphate loss in phosphopeptides upon collision-induced dissociation tandem mass spectrometry (CID MS/MS), the underlying mechanism remains unknown. Here, we explored the mechanism in detail and investigated the selective binding to phosphate groups in solution. Dimetal complexes containing combinations of Ga(3+), In(3+), Fe(3+), Co(3+), Zn(2+), Cu(2+), and V(2+) were reacted with HPO4(2-), phosphoserine, and a phosphopeptide (FQpSEEQQQTEDELQDK, abbreviated "βcas") and studied with isothermal titration calorimetry (ITC), CID MS/MS, and density functional theory (DFT). Ka for HPO4(2-) binding scaled with the metal charge and was 35-fold larger for [LGa2(OH)2(H2O)2](3+) (3.08 ± 0.31 × 10(6) M(-1)) than for [LZn2(HCOO)2](+). CID MS/MS of [LGa2(βcas)](n+) revealed protection against phosphate detachment (<3% of the total ion intensity). Phosphate detachment from βcas was 22-40% and increased to 42-71% when bound to dimetal complexes of lower charge than {LGa2}(5+). CID data suggests that facile metal-phosphate dissociation is associated with proton transfer from the intermediate oxazoline ring formed in the phosphopeptide to the metal-phosphate complex. The observed phosphate stabilization was attributed to a significant reduction in the gas-phase basicity (GB) of the phosphate group when bound to {LGa2}(5+)/{LIn2}(5+) complex cores. Absence of proton transfer results in formation of an ion-zwitterion intermediate with a greater dissociation threshold. This hypothesis is supported by DFT calculations for [LGa2(PO4)](2+), [LGaZn(PO4)](+), [LZn2(PO4)], and 2,4-dimethyl-3-oxazoline showing that [LGa2(PO4)](2+) is the only compound with a substantial lower GB (321 kJ/mol less) than 2,4-dimethyl-3-oxazoline.
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http://dx.doi.org/10.1021/acs.analchem.5b00257DOI Listing
July 2015

Activity-regulating structural changes and autoantibody epitopes in transglutaminase 2 assessed by hydrogen/deuterium exchange.

Proc Natl Acad Sci U S A 2014 Dec 17;111(48):17146-51. Epub 2014 Nov 17.

Centre for Immune Regulation and Department of Immunology, University of Oslo and Oslo University Hospital, N-0372 Oslo, Norway; and

The multifunctional enzyme transglutaminase 2 (TG2) is the target of autoantibodies in the gluten-sensitive enteropathy celiac disease. In addition, the enzyme is responsible for deamidation of gluten peptides, which are subsequently targeted by T cells. To understand the regulation of TG2 activity and the enzyme's role as an autoantigen in celiac disease, we have addressed structural properties of TG2 in solution by using hydrogen/deuterium exchange monitored by mass spectrometry. We demonstrate that Ca(2+) binding, which is necessary for TG2 activity, induces structural changes in the catalytic core domain of the enzyme. Cysteine oxidation was found to abolish these changes, suggesting a mechanism whereby disulfide bond formation inactivates the enzyme. Further, by using TG2-specific human monoclonal antibodies generated from intestinal plasma cells of celiac disease patients, we observed that binding of TG2 by autoantibodies can induce structural changes that could be relevant for the pathogenesis. Detailed mapping of two of the main epitopes targeted by celiac disease autoantibodies revealed that they are located adjacent to each other in the N-terminal part of the TG2 molecule.
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http://dx.doi.org/10.1073/pnas.1407457111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4260576PMC
December 2014

Measuring the hydrogen/deuterium exchange of proteins at high spatial resolution by mass spectrometry: overcoming gas-phase hydrogen/deuterium scrambling.

Acc Chem Res 2014 Oct 29;47(10):3018-27. Epub 2014 Aug 29.

Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen , DK-2100 Copenhagen, Denmark.

Proteins are dynamic molecules that exhibit conformational flexibility to function properly. Well-known examples of this are allosteric regulation of protein activity and ligand-induced conformational changes in protein receptors. Detailed knowledge of the conformational properties of proteins is therefore pertinent to both basic and applied research, including drug development, since the majority of drugs target protein receptors and a growing number of drugs introduced to the market are therapeutic peptides or proteins. X-ray crystallography provides a static picture at atomic resolution of the lowest-energy structure of the native ensemble. There is a growing need for sensitive analytical tools to explore all of the significant molecular structures in the conformational landscape of proteins. Hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS) has recently emerged as a powerful method for characterizing protein conformational dynamics. The basis of this method is the fact that backbone amides in stable hydrogen-bonded structures (e.g., α-helices and β-sheets) are protected against exchange with the aqueous solvent. All protein structures are dynamic, however, and eventually all of the protecting hydrogen bonds will transiently break as the protein--according to thermodynamic principles--cycles through partially unfolded states that correspond to excited free energy levels. As a result, all of the backbone amides will eventually become temporarily solvent-exposed and exchange-competent over time. Consequently, a folded protein in D2O will gradually incorporate deuterium into its backbone amides, and the kinetics of the process can be readily monitored by mass spectrometry. The deuterium uptake kinetics for the intact protein (global exchange kinetics) represents the sum of the exchange kinetics for the individual backbone amides. Local exchange kinetics is typically achieved by using pepsin digestion under quench conditions (i.e., under cold acidic conditions where the amide hydrogen exchange rate is slowed by many orders of magnitude). The ability to localize the individual deuterated residues (the spatial resolution) is determined by the size (typically ∼7-15 residues) and the number of peptic peptides. These peptides provide a relatively coarse-grained picture of the protein dynamics. A fundamental understanding of the relationship between protein function/dysfunction and conformational dynamics requires in many cases higher resolution and ultimately single-residue resolution. In this Account, we summarize our efforts to achieve single-residue deuterium levels in proteins by electron-based or laser-induced gas-phase fragmentation methods. A crucial analytical requirement for this approach is that the pattern of deuterium labeling from solution is retained in the gas-phase fragment ions. It is therefore essential to control and minimize any occurrence of gas-phase randomization of the solution deuterium label (H/D scrambling) during the MS experiment. For this purpose, we have developed model peptide probes to accurately measure the onset and extent of H/D scrambling. Our analytical procedures to control the occurrence of H/D scrambling are detailed along with the physical parameters that induce it during MS analysis. In light of the growing use of gas-phase dissociation experiments to measure the HDX of proteins in order to obtain a detailed characterization and understanding of the dynamic conformations and interactions of proteins at the molecular level, we discuss the perspectives and challenges of future high-resolution HDX-MS methodology.
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http://dx.doi.org/10.1021/ar500194wDOI Listing
October 2014

Local transient unfolding of native state PAI-1 associated with serpin metastability.

Angew Chem Int Ed Engl 2014 Sep 22;53(37):9751-4. Epub 2014 Jul 22.

Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M (Denmark).

The metastability of the native fold makes serpin (serine protease inhibitor) proteins prone to pathological conformational change, often by insertion of an extra β-strand into the central β-sheet A. How this insertion is made possible is a hitherto unresolved question. By the use of advanced hydrogen/deuterium-exchange mass spectrometry (HDX-MS) it is shown that the serpin plasminogen activator inhibitor 1 (PAI-1) transiently unfolds under native condition, on a second-to-minute time scale. The unfolding regions comprise β-strand 5A as well as the underlying hydrophobic core, including β-strand 6B and parts of helices A, B, and C. Based thereon, a mechanism is proposed by which PAI-1 makes transitions through progressively more unfolded states along the reaction coordinate to the inactive, so-called latent form. Our results highlight the profound utility of HDX-MS in detecting sparsely populated, transiently unfolded protein states.
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http://dx.doi.org/10.1002/anie.201402796DOI Listing
September 2014

On the photostability of peptides after selective photoexcitation of the backbone: prompt versus slow dissociation.

Phys Chem Chem Phys 2014 Aug;16(30):15831-8

Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark.

Vulnerability of biomolecules to ultraviolet radiation is intimately linked to deexcitation pathways: photostability requires fast internal conversion to the electronic ground state, but also intramolecular vibrational redistribution and cooling on a time scale faster than dissociation. Here we present a protocol to disentangle slow and non-hazardous statistical dissociation from prompt cleavage of peptide bonds by 210 nm light based on experiments on protonated peptides isolated in vacuo and tagged by 18-crown-6 ether (CE). The weakest link in the system is between the charged site and CE, which is remote from the initial site of excitation. Hence loss of CE serves as direct proof that energy has reached the charge-site end, leaving the backbone intact. Our work demonstrates that excitation of tertiary amide moieties (proline linkages) results in both prompt dissociation and statistical dissociation after energy randomisation over all vibrational degrees of freedom.
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http://dx.doi.org/10.1039/c4cp02015dDOI Listing
August 2014

Molecular mechanism of regulation of the atypical protein kinase C by N-terminal domains and an allosteric small compound.

Chem Biol 2014 Jun 15;21(6):754-65. Epub 2014 May 15.

Research Group PhosphoSites, Department of Internal Medicine I, Universitätsklinikum Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt, Germany. Electronic address:

Protein kinases play important regulatory roles in cells and organisms. Therefore, they are subject to specific and tight mechanisms of regulation that ultimately converge on the catalytic domain and allow the kinases to be activated or inhibited only upon the appropriate stimuli. AGC protein kinases have a pocket in the catalytic domain, the PDK1-interacting fragment (PIF)-pocket, which is a key mediator of the activation. We show here that helix αC within the PIF-pocket of atypical protein kinase C (aPKC) is the target of the interaction with its inhibitory N-terminal domains. We also provide structural evidence that the small compound PS315 is an allosteric inhibitor that binds to the PIF-pocket of aPKC. PS315 exploits the physiological dynamics of helix αC for its binding and allosteric inhibition. The results will support research on allosteric mechanisms and selective drug development efforts against PKC isoforms.
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http://dx.doi.org/10.1016/j.chembiol.2014.04.007DOI Listing
June 2014

Co-existence of two different α-synuclein oligomers with different core structures determined by hydrogen/deuterium exchange mass spectrometry.

Angew Chem Int Ed Engl 2014 Jul 16;53(29):7560-3. Epub 2014 Apr 16.

Interdisciplinary Nanoscience Center (iNANO), Department of Molecular Biology and Genetics, Center for Insoluble Protein Structures (inSPIN), Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C (Denmark).

Neurodegenerative disorders are characterized by the formation of protein oligomers and amyloid fibrils, which in the case of Parkinson's disease involves the protein α-synuclein (αSN). Cytotoxicity is mainly associated with the oligomeric species, but we still know little about their assembly and structure. Hydrogen/deuterium exchange (HDX) monitored by mass spectrometry is used to analyze oligomers formed by wild-type (wt) αSN and also three familial αSN mutants (A30P, E46K, and A53T). All four variants show co-existence of two different oligomers. The backbone amides of oligomer type I are protected from exchange with D2 O until they dissociate into monomeric αSN by EX1 exchange kinetics. Fewer residues are protected against exchange in oligomer type II, but this type does not revert to αSN monomers. Both oligomers are protected in the core sequence Y39-A89. Based on incubation studies, oligomer type I appears to form straight fibrils, while oligomer type II forms amorphous clusters that do not directly contribute to the fibrillation process.
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http://dx.doi.org/10.1002/anie.201400491DOI Listing
July 2014

A phosphorylation tag for uranyl mediated protein purification and photo assisted tag removal.

PLoS One 2014 5;9(3):e91138. Epub 2014 Mar 5.

Department of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Copenhagen N, Denmark.

Most protein purification procedures include an affinity tag fused to either the N or C-terminal end of the protein of interest as well as a procedure for tag removal. Tag removal is not straightforward and especially tag removal from the C-terminal end is a challenge due to the characteristics of enzymes available for this purpose. In the present study, we demonstrate the utility of the divalent uranyl ion in a new procedure for protein purification and tag removal. By employment of a GFP (green florescence protein) recombinant protein we show that uranyl binding to a phosphorylated C-terminal tag enables target protein purification from an E. coli extract by immobilized uranyl affinity chromatography. Subsequently, the tag can be efficiently removed by UV-irradiation assisted uranyl photocleavage. We therefore suggest that the divalent uranyl ion (UO22+) may provide a dual function in protein purification and subsequent C-terminal tag removal procedures.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0091138PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3945016PMC
November 2014

Electrochemical reduction of disulfide-containing proteins for hydrogen/deuterium exchange monitored by mass spectrometry.

Anal Chem 2014 Jan 23;86(1):340-5. Epub 2013 Dec 23.

Department of Biochemistry and Molecular Biology, University of Southern Denmark , Campusvej 55, Odense M DK-5230, Denmark.

Characterization of disulfide bond-containing proteins by hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS) requires reduction of the disulfide bonds under acidic and cold conditions, where the amide hydrogen exchange reaction is quenched (pH 2.5, 0 °C). The reduction typically requires a high concentration (>200 mM) of the chemical reducing agent Tris(2-carboxyethyl)phosphine (TCEP) as its reduction rate constant is decreased at low pH and temperature. Serious adverse effects on chromatographic and mass spectrometric performances have been reported when using high concentrations of TCEP. In the present study, we explore the feasibility of using electrochemical reduction as a substitute for TCEP in HDX-MS analyses. Our results demonstrate that efficient disulfide bond reduction is readily achieved by implementing an electrochemical cell into the HDX-MS workflow. We also identify some challenges in using electrochemical reduction in HDX-MS analyses and provide possible conditions to attenuate these limitations. For example, high salt concentrations hamper disulfide bond reduction, necessitating additional dilution of the sample with aqueous acidic solution at quench conditions.
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http://dx.doi.org/10.1021/ac403269aDOI Listing
January 2014

Characterizing the dynamics of α-synuclein oligomers using hydrogen/deuterium exchange monitored by mass spectrometry.

Biochemistry 2013 Dec 11;52(51):9097-103. Epub 2013 Dec 11.

Department of Biochemistry and Molecular Biology, University of Southern Denmark , 5230 Odense M, Denmark.

Soluble oligomers formed by α-synuclein (αSN) are suspected to play a central role in neuronal cell death during Parkinson's disease. While studies have probed the surface structure of these oligomers, little is known about the backbone dynamics of αSN when they form soluble oligomers. Using hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS), we have analyzed the structural dynamics of soluble αSN oligomers. The analyzed oligomers were metastable, slowly dissociating to monomers over a period of 21 days, after excess monomer had been removed. The C-terminal region of αSN (residues 94-140) underwent isotopic exchange very rapidly, demonstrating a highly dynamic region in the oligomeric state. Three regions (residues 4-17, 39-54, and 70-89) were strongly protected against isotopic exchange in the oligomers, indicating the presence of a stable hydrogen-bonded or solvent-shielded structure. The protected regions were interspersed by two somewhat more dynamic regions (residues 18-38 and 55-70). In the oligomeric state, the isotopic exchange pattern of the region of residues 35-95 of αSN corresponded well with previous nuclear magnetic resonance and electron paramagnetic resonance analyses performed on αSN fibrils and indicated a possible zipperlike maturation mechanism for αSN aggregates. We find the protected N-terminus (residues 4-17) to be of particular interest, as this region has previously been observed to be highly dynamic for both monomeric and fibrillar αSN. This region has mainly been described in relation to membrane binding of αSN, and structuring may be important in relation to disease.
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http://dx.doi.org/10.1021/bi4009193DOI Listing
December 2013