Publications by authors named "Susan Buchanan"

106 Publications

Persistent and toxic chemical pollutants in fish consumed by Asians in Chicago, United States.

Sci Total Environ 2022 Mar 7;811:152214. Epub 2021 Dec 7.

School of Public Health, University of Illinois at Chicago, Chicago, IL 60612, United States. Electronic address:

Consumption of seafood brings health benefits but may increase the ingestion of contaminants. Compared with other ethnic groups in the U.S., Asians consume seafood more frequently. However, there is little information about how culturally specific fish consumption contributes to exposure to toxicants. In this work, we surveyed fish consumption among Chinese, Korean and Vietnamese communities and purchased 103 seafood samples from local markets in Chicago. Each sample was analyzed for mercury (Hg) and 92 organic chemicals including polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), and Dechlorane Plus and related compounds (DPs). The rank order of pollutant concentration in all samples was Hg ≫ ΣPCBs > ΣOCPs > ΣPBDEs > ΣDPs. Positive correlations were noted among most contaminant groups. Bluefish, pike and tuna steak had the highest mean Hg (>1 mg/kg). The mean ΣPCBs was highest in pike and bluefish (>100 ng/g) followed by pollock and mackerel (>40 ng/g). Overall, octopus, shrimp and tilapia were the least contaminated; while pike, bluefish, and pollock were the most contaminated. Omega-3 fatty acids were more strongly affiliated with the organic contaminants than mercury. A risk assessment identified seven types of fish that should have consumption limitations and six that should not be consumed. For these seafoods, consumption advice based on Hg levels would adequately protect health. In the survey participants, 17% of seafood mass consumed is from types of fish that should be limited to 1 or 2 meals/week, while 7% of the seafood mass consumed comes from types that should not be consumed at all. This work adds additional contaminants to the profile of health risks resulting from fish consumption among Asian Americans, which can be used in interventions aimed at conserving consumption of healthy fish while avoiding contaminants.
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http://dx.doi.org/10.1016/j.scitotenv.2021.152214DOI Listing
March 2022

Patient, Family, and Clinician Perspectives on End-of-Life Care Quality Domains and Candidate Indicators for Adolescents and Young Adults With Cancer.

JAMA Netw Open 2021 08 2;4(8):e2121888. Epub 2021 Aug 2.

Division of Research, Kaiser Permanente Northern California, Oakland.

Importance: End-of-life care quality indicators specific to adolescents and young adults (AYAs) aged 12 to 39 years with cancer have not been developed.

Objective: To identify priority domains for end-of-life care from the perspectives of AYAs, family caregivers, and clinicians, and to propose candidate quality indicators reflecting priorities.

Design, Setting, And Participants: This qualitative study was conducted from December 6, 2018, to January 5, 2021, with no additional follow-up. In-depth interviews were conducted with patients, family caregivers, and clinicians and included a content analysis of resulting transcripts. A multidisciplinary advisory group translated priorities into proposed quality indicators. Interviews were conducted at the Dana-Farber Cancer Institute, Kaiser Permanente Northern California, Kaiser Permanente Southern California, and an AYA cancer support community (lacunaloft.org). Participants included 23 AYAs, 28 caregivers, and 29 clinicians.

Exposure: Stage IV or recurrent cancer.

Main Outcomes And Measures: Care priorities.

Results: Interviews were conducted with 23 patients (mean [SD] age, 29.3 [7.3] years; 12 men [52%]; 18 White participants [78%]), 28 family caregivers (23 women [82%]; 14 White participants [50%]), and 29 clinicians (20 women [69%]; 13 White participants [45%]). Caregivers included 22 parents (79%), 5 spouses or partners (18%), and 1 other family member (4%); the 29 clinicians included 15 physicians (52%), 6 nurses or nurse practitioners (21%), and 8 social workers or psychologists (28%). Interviews identified 7 end-of-life priority domains: attention to physical symptoms, attention to quality of life, psychosocial and spiritual care, communication and decision-making, relationships with clinicians, care and treatment, and independence. Themes were consistent across the AYA age range and participant type. Although some domains were represented in quality indicators developed for adults, unique domains were identified, as well as AYA-specific manifestations of existing domains. For example, quality of life included global quality of life; attainment of life goals, legacy, and meaning; support of personal relationships; and normalcy. Within communication and decision-making, domains included communication early in the disease course, addressing prognosis and what to expect at the end of life, and opportunity for AYAs to hold desired roles in decision-making. Care and treatment domains relevant to cancer therapy, use of life-prolonging measures, and location of death emphasized the need for preference sensitivity rather than a standard path. This finding differs from existing adult indicators that propose that late-life chemotherapy, intensive measures, and hospital death should be rare.

Conclusions And Relevance: The findings of this qualitative study suggest that AYAs with cancer have priorities for care at the end of life that are not fully encompassed in existing indicators for adults. Use of new indicators for this young population may better reflect patient- and family-centered experiences of quality care.
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http://dx.doi.org/10.1001/jamanetworkopen.2021.21888DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8383130PMC
August 2021

The Role of Voltage-Dependent Anion Channel in Mitochondrial Dysfunction and Human Disease.

Cells 2021 07 9;10(7). Epub 2021 Jul 9.

Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.

The voltage-dependent anion channel (VDAC) is a β-barrel membrane protein located in the outer mitochondrial membrane (OMM). VDAC has two conductance states: an open anion selective state, and a closed and slightly cation-selective state. VDAC conductance states play major roles in regulating permeability of ATP/ADP, regulation of calcium homeostasis, calcium flux within ER-mitochondria contact sites, and apoptotic signaling events. Three reported structures of VDAC provide information on the VDAC open state via X-ray crystallography and nuclear magnetic resonance (NMR). Together, these structures provide insight on how VDAC aids metabolite transport. The interaction partners of VDAC, together with the permeability of the pore, affect the molecular pathology of diseases including Parkinson's disease (PD), Friedreich's ataxia (FA), lupus, and cancer. To fully address the molecular role of VDAC in disease pathology, major questions must be answered on the structural conformers of VDAC. For example, further information is needed on the structure of the closed state, how binding partners or membrane potential could lead to the open/closed states, the function and mobility of the N-terminal α-helical domain of VDAC, and the physiological role of VDAC oligomers. This review covers our current understanding of the various states of VDAC, VDAC interaction partners, and the roles they play in mitochondrial regulation pertaining to human diseases.
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http://dx.doi.org/10.3390/cells10071737DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8305817PMC
July 2021

A Biochemical and Structural Understanding of TOM Complex Interactions and Implications for Human Health and Disease.

Cells 2021 05 11;10(5). Epub 2021 May 11.

Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.

The central role mitochondria play in cellular homeostasis has made its study critical to our understanding of various aspects of human health and disease. Mitochondria rely on the translocase of the outer membrane (TOM) complex for the bulk of mitochondrial protein import. In addition to its role as the major entry point for mitochondrial proteins, the TOM complex serves as an entry pathway for viral proteins. TOM complex subunits also participate in a host of interactions that have been studied extensively for their function in neurodegenerative diseases, cardiovascular diseases, innate immunity, cancer, metabolism, mitophagy and autophagy. Recent advances in our structural understanding of the TOM complex and the protein import machinery of the outer mitochondrial membrane have made structure-based therapeutics targeting outer mitochondrial membrane proteins during mitochondrial dysfunction an exciting prospect. Here, we describe advances in understanding the TOM complex, the interactome of the TOM complex subunits, the implications for the development of therapeutics, and our understanding of the structure/function relationship between components of the TOM complex and mitochondrial homeostasis.
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http://dx.doi.org/10.3390/cells10051164DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8150904PMC
May 2021

Protein import and export across the bacterial outer membrane.

Curr Opin Struct Biol 2021 08 23;69:55-62. Epub 2021 Apr 23.

Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA. Electronic address:

The bacterial outer membrane forms an impermeable barrier to the environment, but a wide variety of substances must cross it without compromising the membrane. Perhaps, the most fascinating transport phenomenon is the import and export of very large protein toxins using relatively small β-barrel proteins residing in the outer membrane. Progress has been made on three systems in recent years that shed light on this process. In this review, we summarize bacteriocin (toxin) import using TonB-dependent transporters and protein secretion by autotransporters and two partner secretion systems.
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http://dx.doi.org/10.1016/j.sbi.2021.03.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8405454PMC
August 2021

Building Better Barrels - β-barrel Biogenesis and Insertion in Bacteria and Mitochondria.

J Mol Biol 2021 08 24;433(16):166894. Epub 2021 Feb 24.

Laboratory of Molecular Biology, National Institute of Diabetes & Digestive & Kidney Diseases, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD 20892, USA. Electronic address:

β-barrel proteins are folded and inserted into outer membranes by multi-subunit protein complexes that are conserved across different types of outer membranes. In Gram-negative bacteria this complex is the barrel-assembly machinery (BAM), in mitochondria it is the sorting and assembly machinery (SAM) complex, and in chloroplasts it is the outer envelope protein Oep80. Mitochondrial β-barrel precursor proteins are translocated from the cytoplasm to the intermembrane space by the translocase of the outer membrane (TOM) complex, and stabilized by molecular chaperones before interaction with the assembly machinery. Outer membrane bacterial BamA interacts with four periplasmic accessory proteins, whereas mitochondrial Sam50 interacts with two cytoplasmic accessory proteins. Despite these major architectural differences between BAM and SAM complexes, their core proteins, BamA and Sam50, seem to function the same way. Based on the new SAM complex structures, we propose that the mitochondrial β-barrel folding mechanism follows the budding model with barrel-switching aiding in the release of new barrels. We also built a new molecular model for Tom22 interacting with Sam37 to identify regions that could mediate TOM-SAM supercomplex formation.
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http://dx.doi.org/10.1016/j.jmb.2021.166894DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8292188PMC
August 2021

Levels of Ethylene Oxide Biomarker in an Exposed Residential Community.

Int J Environ Res Public Health 2020 11 21;17(22). Epub 2020 Nov 21.

Division of Environmental and Occupational Health Sciences, School of Public Health, University of Illinois at Chicago, Chicago, IL 60612, USA.

The purpose of this study was to examine whether there is a difference in ethylene oxide (EtO) biomarker levels based on residential proximity to facilities emitting EtO, a carcinogen. We recruited residents living near two EtO-emitting facilities and administered a questionnaire on items such as address and length of residency, smoking habits, occupational exposures to EtO, and demographics. We also collected venous blood samples to measure an EtO biomarker, hemoglobin adduct N-2-hydroxyethyl-valine (HbEO), and cotinine, a metabolite of nicotine. Questionnaires and blood samples were collected from 93 participants. The overall geometric HbEO adduct level was 35.0 pmol/gmHb and for nonsmokers it was 29.7 pmol/gmHb. Mean HbEO adduct levels were not significantly associated with sex, age, race, BMI, or education level. HbEO adduct levels for nonsmoking participants who lived in a neighborhood approximately 0.8 km from one of the facilities were significantly higher compared to persons living farther away ( < 0.001). These results suggest that facilities that emit EtO may put nearby communities at risk of cancer and other associated health outcomes.
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http://dx.doi.org/10.3390/ijerph17228646DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7700168PMC
November 2020

Author Correction: Cryo-EM structure of the bacterial Ton motor subcomplex ExbB-ExbD provides information on structure and stoichiometry.

Commun Biol 2020 Nov 9;3(1):676. Epub 2020 Nov 9.

Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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http://dx.doi.org/10.1038/s42003-020-01427-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7652868PMC
November 2020

Ton motor complexes.

Curr Opin Struct Biol 2021 04 3;67:95-100. Epub 2020 Nov 3.

Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA.

The Ton complex is a molecular motor that uses the proton gradient at the inner membrane of Gram-negative bacteria to apply forces on outer membrane proteins, allowing active transport of nutrients into the periplasmic space. For decades, contradictory data has been reported on the structure and stoichiometry of the Ton complex. However, recent reports strongly support a subunit stoichiometry of 5:2 for the ExbB-ExbD subcomplex. In this review, we summarize the recent discoveries of the structures and proposed mechanisms of the Ton system, as well as similar protein motor complexes in Gram-negative bacteria.
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http://dx.doi.org/10.1016/j.sbi.2020.09.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8089110PMC
April 2021

In-depth interrogation of protein thermal unfolding data with MoltenProt.

Protein Sci 2021 01 21;30(1):201-217. Epub 2020 Nov 21.

Centre for Structural Systems Biology (CSSB), Hamburg, Germany.

Protein stability is a key factor in successful structural and biochemical research. However, the approaches for systematic comparison of protein stability are limited by sample consumption or compatibility with sample buffer components. Here we describe how miniaturized measurement of intrinsic tryptophan fluorescence (NanoDSF assay) in combination with a simplified description of protein unfolding can be used to interrogate the stability of a protein sample. We demonstrate that improved protein stability measures, such as apparent Gibbs free energy of unfolding, rather than melting temperature T , should be used to rank the results of thermostability screens. The assay is compatible with protein samples of any composition, including protein complexes and membrane proteins. Our data analysis software, MoltenProt, provides an easy and robust way to perform characterization of multiple samples. Potential applications of MoltenProt and NanoDSF include buffer and construct optimization for X-ray crystallography and cryo-electron microscopy, screening for small-molecule binding partners and comparison of effects of point mutations.
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http://dx.doi.org/10.1002/pro.3986DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7737771PMC
January 2021

Structural insight into toxin secretion by contact-dependent growth inhibition transporters.

Elife 2020 10 22;9. Epub 2020 Oct 22.

Laboratory of Molecular Biology, NIDDK, NIH, Bethesda, United States.

Bacterial contact-dependent growth inhibition (CDI) systems use a type Vb secretion mechanism to export large CdiA toxins across the outer membrane by dedicated outer membrane transporters called CdiB. Here, we report the first crystal structures of two CdiB transporters from and . CdiB transporters adopt a TpsB fold, containing a 16-stranded transmembrane β-barrel connected to two periplasmic domains. The lumen of the CdiB pore is occluded by an N-terminal α-helix and the conserved extracellular loop 6; these two elements adopt different conformations in the structures. We identified a conserved DxxG motif located on strand β1 that connects loop 6 through different networks of interactions. Structural modifications of DxxG induce rearrangement of extracellular loops and alter interactions with the N-terminal α-helix, preparing the system for α-helix ejection. Using structural biology, functional assays, and molecular dynamics simulations, we show how the barrel pore is primed for CdiA toxin secretion.
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http://dx.doi.org/10.7554/eLife.58100DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7644211PMC
October 2020

Exposure characteristics for congeners, isomers, and enantiomers of perfluoroalkyl substances in mothers and infants.

Environ Int 2020 11 6;144:106012. Epub 2020 Aug 6.

Ministry of Education Key Laboratory of Environmental Remediation and Ecosystem Health, Institution of Environmental Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China. Electronic address:

Per- and polyfluoroalkyl substances (PFASs) are ubiquitous in the environment, making it inevitable for humans to be exposed to these pollutants. The exposure begins while in utero and continues in infancy, during the potentially most sensitive early stages of life. This review summarizes the current knowledge on pre- and neo-natal exposures based on more than 200 articles published from 2000 to date. All relevant biological matrices used in the cited studies were included, such as maternal blood, umbilical cord blood, breast milk, placenta, amniotic fluid, fetal organs, newborns' dried blood spots, and infant serum. We show that such exposures are geographically global with significant discrepancies among countries and continents, and that while the levels of major legacy PFASs (PFOS and PFOA) have declined since 2000, those of others may have not. We also show that levels of PFOS and PFOA exceed those of some major environmental toxins, such as p,p'-DDE, BDE-47, PCB-153, PBB-153, and OH-PBDEs in maternal blood. Given that the behavior and potential effects have an origin in molecular structure, biomonitoring and research at the levels of isomers and enantiomers are critically important. Through critical analysis of these works, we summarize the major achievements, consensus, and the deficiencies of existing research. To our knowledge, this is the first review on the overall internal exposure status of mothers and infants to PFASs during pregnancy and lactation.
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http://dx.doi.org/10.1016/j.envint.2020.106012DOI Listing
November 2020

Structural insight into mitochondrial β-barrel outer membrane protein biogenesis.

Nat Commun 2020 07 3;11(1):3290. Epub 2020 Jul 3.

Laboratory of Molecular Biology, National Institute of Diabetes & Digestive & Kidney Diseases, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD, 20892, USA.

In mitochondria, β-barrel outer membrane proteins mediate protein import, metabolite transport, lipid transport, and biogenesis. The Sorting and Assembly Machinery (SAM) complex consists of three proteins that assemble as a 1:1:1 complex to fold β-barrel proteins and insert them into the mitochondrial outer membrane. We report cryoEM structures of the SAM complex from Myceliophthora thermophila, which show that Sam50 forms a 16-stranded transmembrane β-barrel with a single polypeptide-transport-associated (POTRA) domain extending into the intermembrane space. Sam35 and Sam37 are located on the cytosolic side of the outer membrane, with Sam35 capping Sam50, and Sam37 interacting extensively with Sam35. Sam35 and Sam37 each adopt a GST-like fold, with no functional, structural, or sequence similarity to their bacterial counterparts. Structural analysis shows how the Sam50 β-barrel opens a lateral gate to accommodate its substrates.
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http://dx.doi.org/10.1038/s41467-020-17144-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7335169PMC
July 2020

Cloning and Multi-Subunit Expression of Mitochondrial Membrane Protein Complexes in Saccharomyces cerevisiae.

Methods Mol Biol 2020 ;2127:1-11

Laboratory of Molecular Biology, National Institute of Diabetes & Digestive & Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.

Saccharomyces cerevisiae is a useful eukaryotic expression system for mitochondrial membrane proteins due to its ease of growth and ability to provide a native membrane environment. The development of the pBEVY vector system has further increased the potential of S. cerevisiae as an expression system by creating a method for expressing multiple proteins simultaneously. This vector system is amenable to the expression and purification of multi-subunit protein complexes. Here we describe the cloning, yeast transformation, and co-expression of multi-subunit outer mitochondrial membrane complexes using the pBEVY vector system.
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http://dx.doi.org/10.1007/978-1-0716-0373-4_1DOI Listing
March 2021

Structure and Stoichiometry of the Ton Molecular Motor.

Int J Mol Sci 2020 Jan 7;21(2). Epub 2020 Jan 7.

National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA.

The Ton complex is a molecular motor that uses the proton gradient at the inner membrane of Gram-negative bacteria to generate force and movement, which are transmitted to transporters at the outer membrane, allowing the entry of nutrients into the periplasmic space. Despite decades of investigation and the recent flurry of structures being reported by X-ray crystallography and cryoEM, the mode of action of the Ton molecular motor has remained elusive, and the precise stoichiometry of its subunits is still a matter of debate. This review summarizes the latest findings on the Ton system by presenting the recently reported structures and related reports on the stoichiometry of the fully assembled complex.
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http://dx.doi.org/10.3390/ijms21020375DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7014051PMC
January 2020

Cryo-EM structure of the bacterial Ton motor subcomplex ExbB-ExbD provides information on structure and stoichiometry.

Commun Biol 2019 4;2:358. Epub 2019 Oct 4.

1Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892 USA.

The TonB-ExbB-ExbD molecular motor harnesses the proton motive force across the bacterial inner membrane to couple energy to transporters at the outer membrane, facilitating uptake of essential nutrients such as iron and cobalamine. TonB physically interacts with the nutrient-loaded transporter to exert a force that opens an import pathway across the outer membrane. Until recently, no high-resolution structural information was available for this unique molecular motor. We published the first crystal structure of ExbB-ExbD in 2016 and showed that five copies of ExbB are arranged as a pentamer around a single copy of ExbD. However, our spectroscopic experiments clearly indicated that two copies of ExbD are present in the complex. To resolve this ambiguity, we used single-particle cryo-electron microscopy to show that the ExbB pentamer encloses a dimer of ExbD in its transmembrane pore, and not a monomer as previously reported. The revised stoichiometry has implications for motor function.
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http://dx.doi.org/10.1038/s42003-019-0604-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6778125PMC
May 2020

Structure of voltage-dependent anion channel-tethered bilayer lipid membranes determined using neutron reflectivity.

Acta Crystallogr D Struct Biol 2018 Dec 30;74(Pt 12):1219-1232. Epub 2018 Nov 30.

Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20878, USA.

Neutron reflectivity (NR) has emerged as a powerful technique to study the structure and behavior of membrane proteins at planar lipid interfaces. Integral membrane proteins (IMPs) remain a significant challenge for NR owing to the difficulty of forming complete bilayers with sufficient protein density for scattering techniques. One strategy to achieve high protein density on a solid substrate is the capture of detergent-stabilized, affinity-tagged IMPs on a nitrilotriacetic acid (NTA)-functionalized self-assembled monolayer (SAM), followed by reconstitution into the lipids of interest. Such protein-tethered bilayer lipid membranes (ptBLMs) have the notable advantage of a uniform IMP orientation on the substrate. Here, NR is used to provide a structural characterization of the ptBLM process from formation of the SAM to capture of the detergent-stabilized IMP and lipid reconstitution. The mitochondrial outer-membrane voltage-dependent anion channel (VDAC), which controls the exchange of bioenergetic metabolites between mitochondria and the cytosol, was used as a model β-barrel IMP. Molecular dynamics simulations were used for comparison with the experimental results and to inform the parameters of the physical models describing the NR data. The detailed structure of the SAM is shown to depend on the density of the NTA chelating groups. The relative content of detergent and protein in surface-immobilized, detergent-stabilized VDAC is measured, while the reconstituted lipid bilayer is shown to be complete to within a few percent, using the known atomic structure of VDAC. Finally, excess lipid above the reconstituted bilayer, which is of consequence for more indirect structural and functional studies, is shown to be present.
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http://dx.doi.org/10.1107/S2059798318011749DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6317592PMC
December 2018

Health and Safety of Limited English Speaking Asian Homecare Aides in Chicago: A Pilot Study.

J Occup Environ Med 2019 01;61(1):81-88

Division of Environmental and Occupational Health Sciences, School of Public Health (Dr Zhang, Dr Buchanan, Dr Zanoni); and College of Medicine (Dr Rospenda), University of Illinois at Chicago, Chicago, Illinois.

Objectives: To identify health and safety hazards and needs among limited English speaking Asian home care aides, and characterize their acculturation status and how it affects their health and safety.

Methods: Surveyed 60 home care aides and interviewed six home care service providers to assess health and safety hazards and needs of the study population.

Results: The majority of the study participants were older and did not speak English or did not speak English well. They communicated with senior clients in their native language only or most of the time. Many experienced work related injuries and musculoskeletal pain.

Discussion: The Asian homecare aides met the critical needs of an aging community. They experienced many challenges working as a home care aide and as a result of cultural barriers.
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http://dx.doi.org/10.1097/JOM.0000000000001495DOI Listing
January 2019

Editorial overview: Membranes and their embedded molecular machines.

Curr Opin Struct Biol 2018 08;51:vii-viii

NIDDK, United States.

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http://dx.doi.org/10.1016/j.sbi.2018.10.005DOI Listing
August 2018

Hitting with a BAM: Selective Killing by Lectin-Like Bacteriocins.

mBio 2018 03 20;9(2). Epub 2018 Mar 20.

Centre of Microbial and Plant Genetics, KU Leuven, Heverlee, Belgium.

Lectin-like bacteriocins (LlpAs) are secreted by proteobacteria and selectively kill strains of their own or related species, and they are composed of two B-lectin domains with divergent sequences. In spp., initial binding of these antibacterial proteins to cells is mediated by the carboxy-terminal domain through d-rhamnose residues present in the common polysaccharide antigen of their lipopolysaccharide, whereas the amino-terminal domain accounts for strain selectivity of killing. Here, we show that spontaneous LlpA-resistant mutants carry mutations in one of three surface-exposed moieties of the essential β-barrel outer membrane protein insertase BamA, the core component of the BAM complex. Polymorphism of this loop in different groups is linked to LlpA susceptibility, and targeted cells all share the same signature motif in this loop. Since heterologous expression of such a gene confers LlpA susceptibility upon a resistant strain, BamA represents the primary bacteriocin selectivity determinant in pseudomonads. Contrary to modular bacteriocins that require uptake via the Tol or Ton system, parasitism of BamA as an LlpA receptor advocates a novel bacteriocin killing mechanism initiated by impairment of the BAM machinery. Bacteria secrete a variety of molecules to eliminate microbial rivals. Bacteriocins are a pivotal group of peptides and proteins that assist in this fight, specifically killing related bacteria. In Gram-negative bacteria, these antibacterial proteins often comprise distinct domains for initial binding to a target cell's surface and subsequent killing via enzymatic or pore-forming activity. Here, we show that lectin-like bacteriocins, a family of bacteriocins that lack the prototypical modular toxin architecture, also stand out by parasitizing BamA, the core component of the outer membrane protein assembly machinery. A particular surface-exposed loop of BamA, critical for its function, serves as a key discriminant for cellular recognition, and polymorphisms in this loop determine whether a strain is susceptible or immune to a particular bacteriocin. These findings suggest a novel mechanism of contact-dependent killing that does not require cellular uptake. The evolutionary advantage of piracy of an essential cellular compound is highlighted by the observation that contact-dependent growth inhibition, a distinct antagonistic system, can equally take advantage of this receptor.
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http://dx.doi.org/10.1128/mBio.02138-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5874912PMC
March 2018

The ColM Family, Polymorphic Toxins Breaching the Bacterial Cell Wall.

mBio 2018 02 13;9(1). Epub 2018 Feb 13.

Centre of Microbial and Plant Genetics, KU Leuven, Heverlee, Belgium.

Bacteria host an arsenal of antagonism-mediating molecules to combat for ecologic space. Bacteriocins represent a pivotal group of secreted antibacterial peptides and proteins assisting in this fight, mainly eliminating relatives. Colicin M, a model for peptidoglycan-interfering bacteriocins in Gram-negative bacteria, appears to be part of a set of polymorphic toxins equipped with such a catalytic domain (ColM) targeting lipid II. Diversifying recombination has enabled parasitism of different receptors and has also given rise to hybrid bacteriocins in which ColM is associated with another toxin module. Remarkably, ColM toxins have recruited a diverse array of immunity partners, comprising cytoplasmic membrane-associated proteins with different topologies. Together, these findings suggest that different immunity mechanisms have evolved for ColM, in contrast to bacteriocins with nuclease activities.
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http://dx.doi.org/10.1128/mBio.02267-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5821083PMC
February 2018

Structural and functional insights into the role of BamD and BamE within the β-barrel assembly machinery in .

J Biol Chem 2018 01 11;293(4):1106-1119. Epub 2017 Dec 11.

Markey Center for Structural Biology, Department of Biological Sciences and the Purdue Institute of Inflammation, Immunology and Infectious Disease, Purdue University, West Lafayette, Indiana 47907

The β-barrel assembly machinery (BAM) is a conserved multicomponent protein complex responsible for the biogenesis of β-barrel outer membrane proteins (OMPs) in Gram-negative bacteria. Given its role in the production of OMPs for survival and pathogenesis, BAM represents an attractive target for the development of therapeutic interventions, including drugs and vaccines against multidrug-resistant bacteria such as The first structure of BamA, the central component of BAM, was from , the etiological agent of the sexually transmitted disease gonorrhea. To aid in pharmaceutical targeting of BAM, we expanded our studies to BamD and BamE within BAM of this clinically relevant human pathogen. We found that the presence of BamD, but not BamE, is essential for gonococcal viability. However, BamE, but not BamD, was cell-surface-displayed under native conditions; however, in the absence of BamE, BamD indeed becomes surface-exposed. Loss of BamE altered cell envelope composition, leading to slower growth and an increase in both antibiotic susceptibility and formation of membrane vesicles containing greater amounts of vaccine antigens. Both BamD and BamE are expressed in diverse gonococcal isolates, under host-relevant conditions, and throughout different phases of growth. The solved structures of BamD and BamE share overall folds with proteins but contain differences that may be important for function. Together, these studies highlight that, although BAM is conserved across Gram-negative bacteria, structural and functional differences do exist across species, which may be leveraged in the development of species-specific therapeutics in the effort to combat multidrug resistance.
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http://dx.doi.org/10.1074/jbc.RA117.000437DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5787791PMC
January 2018

Association of methylmercury intake from seafood consumption and blood mercury level among the Asian and Non-Asian populations in the United States.

Environ Res 2018 01 8;160:212-222. Epub 2017 Oct 8.

University of Illinois at Chicago, School of Public Health, Division of Epidemiology and Biostatistics, 1603 West Taylor Street, Chicago, IL, USA.

Background: MeHg is a well-established neurotoxicant for fetal brain growth and development and has been shown to increase the risk of cardiovascular disease in aging populations. In the U.S., Asian populations are of particular concern because of their seafood consumption behaviors.

Objectives: Our objective was to calculate the average daily MeHg intake (ADMI) from seafood and to assess the relationship between ADMI with blood methylmercury (BMeHg) concentrations, specifically among women of reproductive age (WORA) and adults ≥ 50 years of age.

Methods: We estimated ADMI from seafood using the 30-day fish consumption data from the NHANES 2011-2014 datasets. Using multivariable linear regression, we estimated the proportional change in mean BMeHg associated with a doubling of the ADMI. Further, correlations between ADMI and BMeHg were compared between Asians and other racial/ethnic groups.

Results: Our analysis found both Asian WORA and Asian adults age ≥ 50 years old had significantly higher BMeHg levels and ADMI than their Non-Asian counterparts. Correlations between ADMI from seafood and blood Hg levels were stronger among Asian WORA than among Non-Asian WORA. Key fish species that influenced the dietary MeHg intake for Asians were mackerel, tuna, and "other known/unknown fish species".

Conclusion: We confirmed that Asian populations have higher MeHg intake than the Non-Asian population in the U.S. and seafood intake is a key predictor of blood Hg concentration, especially among Asian women of reproductive age. Future studies should incorporate information on other known and unknown fish species that are frequently consumed by Asian populations and different parts and fish organs eaten to better understand determinants of MeHg exposure.
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http://dx.doi.org/10.1016/j.envres.2017.09.031DOI Listing
January 2018

Insertion of proteins and lipopolysaccharide into the bacterial outer membrane.

Philos Trans R Soc Lond B Biol Sci 2017 Aug;372(1726)

Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA

The bacterial outer membrane contains phospholipids in the inner leaflet and lipopolysaccharide (LPS) in the outer leaflet. Both proteins and LPS must be frequently inserted into the outer membrane to preserve its integrity. The protein complex that inserts LPS into the outer membrane is called LptDE, and consists of an integral membrane protein, LptD, with a separate globular lipoprotein, LptE, inserted in the barrel lumen. The protein complex that inserts newly synthesized outer-membrane proteins (OMPs) into the outer membrane is called the BAM complex, and consists of an integral membrane protein, BamA, plus four lipoproteins, BamB, C, D and E. Recent structural and functional analyses illustrate how these two complexes insert their substrates into the outer membrane by distorting the membrane component (BamA or LptD) to directly access the lipid bilayer.This article is part of the themed issue 'Membrane pores: from structure and assembly, to medicine and technology'.
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http://dx.doi.org/10.1098/rstb.2016.0224DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5483524PMC
August 2017

Two-Partner Secretion: Combining Efficiency and Simplicity in the Secretion of Large Proteins for Bacteria-Host and Bacteria-Bacteria Interactions.

Front Cell Infect Microbiol 2017 9;7:148. Epub 2017 May 9.

Université de Lille, Centre National de La Recherche Scientifique, Institut National de La Santé et de La Recherche Médicale, CHU Lille, Institut Pasteur de Lille, U1019-UMR 8204-Centre d'Infection et d'Immunité de LilleLille, France.

Initially identified in pathogenic Gram-negative bacteria, the two-partner secretion (TPS) pathway, also known as Type Vb secretion, mediates the translocation across the outer membrane of large effector proteins involved in interactions between these pathogens and their hosts. More recently, distinct TPS systems have been shown to secrete toxic effector domains that participate in inter-bacterial competition or cooperation. The effects of these systems are based on kin vs. non-kin molecular recognition mediated by specific immunity proteins. With these new toxin-antitoxin systems, the range of TPS effector functions has thus been extended from cytolysis, adhesion, and iron acquisition, to genome maintenance, inter-bacterial killing and inter-bacterial signaling. Basically, a TPS system is made up of two proteins, the secreted TpsA effector protein and its TpsB partner transporter, with possible additional factors such as immunity proteins for protection against cognate toxic effectors. Structural studies have indicated that TpsA proteins mainly form elongated β helices that may be followed by specific functional domains. TpsB proteins belong to the Omp85 superfamily. Open questions remain on the mechanism of protein secretion in the absence of ATP or an electrochemical gradient across the outer membrane. The remarkable dynamics of the TpsB transporters and the progressive folding of their TpsA partners at the bacterial surface in the course of translocation are thought to be key elements driving the secretion process.
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http://dx.doi.org/10.3389/fcimb.2017.00148DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5422565PMC
December 2017

A Natural Chimeric Bacteriocin with Novel Pore-Forming Activity Parasitizes the Ferrichrome Transporter.

mBio 2017 02 21;8(1). Epub 2017 Feb 21.

Centre of Microbial and Plant Genetics, KU Leuven, Heverlee, Belgium.

Modular bacteriocins represent a major group of secreted protein toxins with a narrow spectrum of activity, involved in interference competition between Gram-negative bacteria. These antibacterial proteins include a domain for binding to the target cell and a toxin module at the carboxy terminus. Self-inhibition of producers is provided by coexpression of linked immunity genes that transiently inhibit the toxin's activity through formation of bacteriocin-immunity complexes or by insertion in the inner membrane, depending on the type of toxin module. We demonstrate strain-specific inhibitory activity for PmnH, a bacteriocin with an unprecedented dual-toxin architecture, hosting both a colicin M domain, potentially interfering with peptidoglycan synthesis, and a novel colicin N-type domain, a pore-forming module distinct from the colicin Ia-type domain in pyocin S5. A downstream-linked gene product confers PmnH immunity upon susceptible strains. This protein, ImnH, has a transmembrane topology similar to that of colicin M-like and pore-forming immunity proteins, although homology with either of these is essentially absent. The enhanced killing activity of PmnH under iron-limited growth conditions reflects parasitism of the ferrichrome-type transporter for entry into target cells, a strategy shown here to be used as well by monodomain colicin M-like bacteriocins from pseudomonads. The integration of a second type of toxin module in a bacteriocin gene could offer a competitive advantage against bacteria displaying immunity against only one of both toxic activities. In their continuous struggle for ecological space, bacteria face a huge load of contenders, including phylogenetically related strains that compete for the same niche. One important group of secreted antibacterial proteins assisting in eliminating these rivals are modular bacteriocins of Gram-negative bacteria, comprising a domain for docking onto the cell envelope of a target cell, a translocation domain enabling subsequent cellular entry, and a toxin module that kills target cells via enzymatic or pore-forming activity. We here demonstrate the antagonistic function of a bacteriocin with unique architecture that combines a putative enzymatic colicin M-like domain and a novel pore-forming toxin module. For target cell recognition and entry, this bacteriocin hybrid takes advantage of the ferrichrome transporter, also parasitized by enzymatic bacteriocins devoid of the pore-forming module. Bacteriocins with an expanded toxin potential may represent an inventive bacterial strategy to alleviate immunity in target cells.
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http://dx.doi.org/10.1128/mBio.01961-16DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5358913PMC
February 2017

The β-barrel assembly machinery in motion.

Nat Rev Microbiol 2017 04 20;15(4):197-204. Epub 2017 Feb 20.

National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA.

In Gram-negative bacteria, the biogenesis of β-barrel outer membrane proteins (OMPs) is mediated by the β-barrel assembly machinery (BAM) complex. During the past decade, structural and functional studies have collectively contributed to advancing our understanding of the structure and function of the BAM complex; however, the exact mechanism that is involved remains elusive. In this Progress article, we discuss recent structural studies that have revealed that the accessory proteins may regulate essential unprecedented conformational changes in the core component BamA during function. We also detail the mechanistic insights that have been gained from structural data, mutagenesis studies and molecular dynamics simulations, and explore two emerging models for the BAM-mediated biogenesis of OMPs in bacteria.
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http://dx.doi.org/10.1038/nrmicro.2016.191DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5455337PMC
April 2017

Structural snapshots of the β-barrel assembly machinery.

FEBS J 2017 06 29;284(12):1778-1786. Epub 2016 Nov 29.

Department of Biological Sciences, Markey Center for Structural Biology, Purdue Institute for Inflammation, Immunology and Infectious Diseases, Purdue University, West Lafayette, IN, USA.

The β-barrel assembly machinery (BAM) is a multicomponent complex responsible for the biogenesis of β-barrel outer membrane proteins (OMPs) in Gram-negative bacteria, with conserved systems in both mitochondria and chloroplasts. Given its importance in the integrity of the outer membrane and in the assembly of surface exposed virulence factors, BAM is an attractive therapeutic target against pathogenic bacteria, particularly multidrug-resistant strains. While the mechanism for how BAM functions remains elusive, previous structural studies have described each of the individual components of BAM, offering only a few clues to how the complex functions. Recently, a number of structures have been reported of complexes, including that of fully assembled BAM in differing conformational states. These studies have provided the molecular blueprint detailing the atomic interactions between the components and have revealed new details about BAM, which suggest a dynamic mechanism that may use conformational changes to assist in the biogenesis of new OMPs.
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http://dx.doi.org/10.1111/febs.13960DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5429997PMC
June 2017

Structure of the NPr:EIN Complex: Mechanism for Specificity in Paralogous Phosphotransferase Systems.

Structure 2016 12 10;24(12):2127-2137. Epub 2016 Nov 10.

Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. Electronic address:

Paralogous enzymes arise from gene duplication events that confer a novel function, although it is unclear how cross-reaction between the original and duplicate protein interaction network is minimized. We investigated HPr:EI and NPr:EI, the initial complexes of paralogous phosphorylation cascades involved in sugar import and nitrogen regulation in bacteria, respectively. Although the HPr:EI interaction has been well characterized, involving multiple complexes and transient interactions, the exact nature of the NPr:EI complex was unknown. We set out to identify the key features of the interaction by performing binding assays and elucidating the structure of NPr in complex with the phosphorylation domain of EI (EIN), using a hybrid approach involving X-ray, homology, and sparse nuclear magnetic resonance. We found that the overall fold and active-site structure of the two complexes are conserved in order to maintain productive phosphorylation, however, the interface surface potential differs between the two complexes, which prevents cross-reaction.
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http://dx.doi.org/10.1016/j.str.2016.10.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5143221PMC
December 2016

Tyrosine Kinase Inhibitors for the Treatment of Chronic-Phase Chronic Myeloid Leukemia: Long-Term Patient Care and Management.

J Adv Pract Oncol 2016 Jan-Feb;7(1):42-54. Epub 2016 Jan 1.

1Department of Internal Medicine, Washington University, St. Louis, Missouri; 2Adult Leukemia Program, Dana-Farber Cancer Institute, Boston, Massachusetts; 3Department of Internal Medicine and Department of Hematology/Oncology, University of Michigan Health System, Ann Arbor, Michigan.

Several tyrosine kinase inhibitors (TKIs) are now approved for the treatment of chronic myeloid leukemia in chronic phase. The efficacy of these drugs has been repeatedly demonstrated, as has their tolerability in most patients. However, late and chronic toxicities become an important issue for many patients facing long-term TKI exposure. For patients on long-term imatinib, gastrointestinal events, fluid retention, muscle cramps, fatigue, and hepatotoxicity are among the most common and most clinically relevant adverse events (AEs). A few of these have also emerged as important AEs with some of the newer TKIs. Distinct long-term toxicity concerns have emerged for dasatinib (pleural effusion, pulmonary hypertension, headache, and dyspnea) and nilotinib (rash, headache, myalgia, alopecia, and hyperglycemia), whereas due to the recent approval of bosutinib and ponatinib, their long-term toxicity profiles have not been fully characterized. Clinical experience with each of these drugs is accumulating, and ensuring proper adherence and monitoring for potential AEs is essential for effective treatment.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5045277PMC
http://dx.doi.org/10.6004/jadpro.2016.7.1.3DOI Listing
January 2016
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