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Lewis BR, Uddin MR, Kuo KM, Shah LMN, Harris NJ, Booth PJ, Hammerschmid D, Gumbart JC, Zgurskaya HI, Reading E. Mg 2+-dependent mechanism of environmental versatility in a multidrug efflux pump. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.10.597921. [PMID: 38915626 PMCID: PMC11195059 DOI: 10.1101/2024.06.10.597921] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/26/2024]
Abstract
Tripartite resistance nodulation and cell division multidrug efflux pumps span the periplasm and are a major driver of multidrug resistance among Gram-negative bacteria. The periplasm provides a distinct environment between the inner and outer membranes of Gram-negative bacteria. Cations, such as Mg2+, become concentrated within the periplasm and, in contrast to the cytoplasm, its pH is sensitive to conditions outside the cell. Here, we reveal an interplay between Mg2+ and pH in modulating the dynamics of the periplasmic adaptor protein, AcrA, and its function within the prototypical AcrAB-TolC multidrug efflux pump from Escherichia coli. In the absence of Mg2+, AcrA becomes increasingly plastic within acidic conditions, but when Mg2+ is bound this is ameliorated, resulting in domain specific organisation in neutral to weakly acidic regimes. We establish a unique histidine residue directs these structural dynamics and is essential for sustaining pump efflux activity across acidic, neutral, and alkaline conditions. Overall, we propose Mg2+ conserves the structural mobility of AcrA to ensure optimal AcrAB-TolC function within rapid changing environments commonly faced by the periplasm during bacterial infection and colonization. This work highlights that Mg2+ is an important mechanistic component in this pump class and possibly across other periplasmic lipoproteins.
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Affiliation(s)
- Benjamin Russell Lewis
- Department of Chemistry, Britannia House, 7 Trinity Street, King’s College London, London, SE1 1DB, UK
| | - Muhammad R. Uddin
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, Oklahoma 73019, USA
| | - Katie M. Kuo
- School of Physics, Georgia Institute of Technology, 837 State Street NW, Atlanta, Georgia 30332, USA
| | - Laila M. N. Shah
- Department of Chemistry, Britannia House, 7 Trinity Street, King’s College London, London, SE1 1DB, UK
| | - Nicola J. Harris
- Department of Chemistry, Britannia House, 7 Trinity Street, King’s College London, London, SE1 1DB, UK
| | - Paula J. Booth
- Department of Chemistry, Britannia House, 7 Trinity Street, King’s College London, London, SE1 1DB, UK
| | - Dietmar Hammerschmid
- Department of Chemistry, Britannia House, 7 Trinity Street, King’s College London, London, SE1 1DB, UK
- School of Biological Sciences, University of Southampton, Southampton SO17 1BJ, UK
| | - James C. Gumbart
- School of Physics, Georgia Institute of Technology, 837 State Street NW, Atlanta, Georgia 30332, USA
- School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive NW, Atlanta, Georgia 30332, USA
| | - Helen I. Zgurskaya
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, Oklahoma 73019, USA
| | - Eamonn Reading
- Department of Chemistry, Britannia House, 7 Trinity Street, King’s College London, London, SE1 1DB, UK
- School of Biological Sciences, University of Southampton, Southampton SO17 1BJ, UK
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2
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Nageeb WM, AlHarbi N, Alrehaili AA, Zakai SA, Elfadadny A, Hetta HF. Global genomic epidemiology of chromosomally mediated non-enzymatic carbapenem resistance in Acinetobacter baumannii: on the way to predict and modify resistance. Front Microbiol 2023; 14:1271733. [PMID: 37869654 PMCID: PMC10587612 DOI: 10.3389/fmicb.2023.1271733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 09/05/2023] [Indexed: 10/24/2023] Open
Abstract
Introduction Although carbapenemases are frequently reported in resistant A. baumannii clinical isolates, other chromosomally mediated elements of resistance that are considered essential are frequently underestimated. Having a wide substrate range, multidrug efflux pumps frequently underlie antibiotic treatment failure. Recognizing and exploiting variations in multidrug efflux pumps and penicillin-binding proteins (PBPs) is an essential approach in new antibiotic drug discovery and engineering to meet the growing challenge of multidrug-resistant Gram-negative bacteria. Methods A total of 980 whole genome sequences of A. baumannii were analyzed. Nucleotide sequences for the genes studied were queried against a custom database of FASTA sequences using the Bacterial and Viral Bioinformatics Resource Center (BV-BRC) system. The correlation between different variants and carbapenem Minimum Inhibitory Concentrations (MICs) was studied. PROVEAN and I-Mutant predictor suites were used to predict the effect of the studied amino acid substitutions on protein function and protein stability. Both PsiPred and FUpred were used for domain and secondary structure prediction. Phylogenetic reconstruction was performed using SANS serif and then visualized using iTOL and Phandango. Results Exhibiting the highest detection rate, AdeB codes for an important efflux-pump structural protein. T48V, T584I, and P660Q were important variants identified in the AdeB-predicted multidrug efflux transporter pore domains. These can act as probable targets for designing new efflux-pump inhibitors. Each of AdeC Q239L and AdeS D167N can also act as probable targets for restoring carbapenem susceptibility. Membrane proteins appear to have lower predictive potential than efflux pump-related changes. OprB and OprD changes show a greater effect than OmpA, OmpW, Omp33, and CarO changes on carbapenem susceptibility. Functional and statistical evidence make the variants T636A and S382N at PBP1a good markers for imipenem susceptibility and potential important drug targets that can modify imipenem resistance. In addition, PBP3_370, PBP1a_T636A, and PBP1a_S382N may act as potential drug targets that can be exploited to counteract imipenem resistance. Conclusion The study presents a comprehensive epidemiologic and statistical analysis of potential membrane proteins and efflux-pump variants related to carbapenem susceptibility in A. baumannii, shedding light on their clinical utility as diagnostic markers and treatment modification targets for more focused studies of candidate elements.
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Affiliation(s)
- Wedad M. Nageeb
- Department of Medical Microbiology and Immunology, Faculty of Medicine, Suez Canal University, Ismailia, Egypt
| | - Nada AlHarbi
- Department of Biology, College of Science, Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia
| | - Amani A. Alrehaili
- Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, Taif University, Taif, Saudi Arabia
| | - Shadi A. Zakai
- Department of Clinical Microbiology and Immunology, Faculty of Medicine, King Abdulaziz University, Jeddah, Saudi Arabia
| | - Ahmed Elfadadny
- Department of Animal Internal Medicine, Faculty of Veterinary Medicine, Damanhour University, Damanhour, El-Beheira, Egypt
| | - Helal F. Hetta
- Department of Medical Microbiology and Immunology, Faculty of Medicine, Assiut University, Assiut, Egypt
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3
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Russell Lewis B, Uddin MR, Moniruzzaman M, Kuo KM, Higgins AJ, Shah LMN, Sobott F, Parks JM, Hammerschmid D, Gumbart JC, Zgurskaya HI, Reading E. Conformational restriction shapes the inhibition of a multidrug efflux adaptor protein. Nat Commun 2023; 14:3900. [PMID: 37463890 PMCID: PMC10354078 DOI: 10.1038/s41467-023-39615-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Accepted: 06/15/2023] [Indexed: 07/20/2023] Open
Abstract
Membrane efflux pumps play a major role in bacterial multidrug resistance. The tripartite multidrug efflux pump system from Escherichia coli, AcrAB-TolC, is a target for inhibition to lessen resistance development and restore antibiotic efficacy, with homologs in other ESKAPE pathogens. Here, we rationalize a mechanism of inhibition against the periplasmic adaptor protein, AcrA, using a combination of hydrogen/deuterium exchange mass spectrometry, cellular efflux assays, and molecular dynamics simulations. We define the structural dynamics of AcrA and find that an inhibitor can inflict long-range stabilisation across all four of its domains, whereas an interacting efflux substrate has minimal effect. Our results support a model where an inhibitor forms a molecular wedge within a cleft between the lipoyl and αβ barrel domains of AcrA, diminishing its conformational transmission of drug-evoked signals from AcrB to TolC. This work provides molecular insights into multidrug adaptor protein function which could be valuable for developing antimicrobial therapeutics.
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Affiliation(s)
- Benjamin Russell Lewis
- Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London, SE1 1DB, UK
| | - Muhammad R Uddin
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK, 73019, USA
| | - Mohammad Moniruzzaman
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK, 73019, USA
| | - Katie M Kuo
- School of Chemistry and Biochemistry, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA, 30332, USA
| | - Anna J Higgins
- School of Molecular and Cellular Biology & Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Laila M N Shah
- Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London, SE1 1DB, UK
| | - Frank Sobott
- School of Molecular and Cellular Biology & Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Jerry M Parks
- Bioscience Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN, 37831, USA
| | - Dietmar Hammerschmid
- Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London, SE1 1DB, UK
| | - James C Gumbart
- School of Chemistry and Biochemistry, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA, 30332, USA.
- School of Physics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA, 30332, USA.
| | - Helen I Zgurskaya
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK, 73019, USA.
| | - Eamonn Reading
- Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London, SE1 1DB, UK.
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4
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Cacciotto P, Basciu A, Oliva F, Malloci G, Zacharias M, Ruggerone P, Vargiu AV. Molecular rationale for the impairment of the MexAB-OprM efflux pump by a single mutation in MexA. Comput Struct Biotechnol J 2022; 20:252-260. [PMID: 35024097 PMCID: PMC8717590 DOI: 10.1016/j.csbj.2021.11.042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 11/29/2021] [Accepted: 11/30/2021] [Indexed: 11/16/2022] Open
Abstract
Efflux pumps of the Resistance-Nodulation-cell Division (RND) superfamily contribute to intrinsic and acquired resistance in Gram-negative pathogens by expelling chemically unrelated antibiotics with high efficiency. They are tripartite systems constituted by an inner-membrane-anchored transporter, an outer membrane factor protein, and a membrane fusion protein. Multimerization of the membrane fusion protein is an essential prerequisite for full functionality of these efflux pumps. In this work, we employed complementary computational techniques to investigate the stability of a dimeric unit of MexA (the membrane fusion protein of the MexAB-OprM RND efflux pump of Pseudomonas aeruginosa), and to provide a molecular rationale for the effect of the G72S substitution, which affects MexAB-OprM functionality by impairing the assembly of MexA. Our findings indicate that: i) dimers of this protein are stable in multiple µs-long molecular dynamics simulations; ii) the mutation drastically alters the conformational equilibrium of MexA, favouring a collapsed conformation that is unlikely to form dimers or higher order assemblies. Unveiling the mechanistic aspects underlying large conformational distortions induced by minor sequence changes is informative to efforts at interfering with the activity of this elusive bacterial weapon. In this respect, our work further confirms how molecular simulations can give important contribution and useful insights to characterize the mechanism of highly complex biological systems.
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Affiliation(s)
- Pierpaolo Cacciotto
- Dipartimento di Fisica, Università degli Studi di Cagliari, S.P. Monserrato-Sestu km 0.700, I-09042 Monserrato (CA), Italy
| | - Andrea Basciu
- Dipartimento di Fisica, Università degli Studi di Cagliari, S.P. Monserrato-Sestu km 0.700, I-09042 Monserrato (CA), Italy
| | - Francesco Oliva
- Dipartimento di Fisica, Università degli Studi di Cagliari, S.P. Monserrato-Sestu km 0.700, I-09042 Monserrato (CA), Italy
| | - Giuliano Malloci
- Dipartimento di Fisica, Università degli Studi di Cagliari, S.P. Monserrato-Sestu km 0.700, I-09042 Monserrato (CA), Italy
| | - Martin Zacharias
- Physics Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany
| | - Paolo Ruggerone
- Dipartimento di Fisica, Università degli Studi di Cagliari, S.P. Monserrato-Sestu km 0.700, I-09042 Monserrato (CA), Italy
| | - Attilio V Vargiu
- Dipartimento di Fisica, Università degli Studi di Cagliari, S.P. Monserrato-Sestu km 0.700, I-09042 Monserrato (CA), Italy
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5
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Webber A, Ratnaweera M, Harris A, Luisi BF, Ntsogo Enguéné VY. A Model for Allosteric Communication in Drug Transport by the AcrAB-TolC Tripartite Efflux Pump. Antibiotics (Basel) 2022; 11:52. [PMID: 35052929 PMCID: PMC8773123 DOI: 10.3390/antibiotics11010052] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 12/22/2021] [Accepted: 12/28/2021] [Indexed: 01/30/2023] Open
Abstract
RND family efflux pumps are complex macromolecular machines involved in multidrug resistance by extruding antibiotics from the cell. While structural studies and molecular dynamics simulations have provided insights into the architecture and conformational states of the pumps, the path followed by conformational changes from the inner membrane protein (IMP) to the periplasmic membrane fusion protein (MFP) and to the outer membrane protein (OMP) in tripartite efflux assemblies is not fully understood. Here, we investigated AcrAB-TolC efflux pump's allostery by comparing resting and transport states using difference distance matrices supplemented with evolutionary couplings data and buried surface area measurements. Our analysis indicated that substrate binding by the IMP triggers quaternary level conformational changes in the MFP, which induce OMP to switch from the closed state to the open state, accompanied by a considerable increase in the interface area between the MFP subunits and between the OMPs and MFPs. This suggests that the pump's transport-ready state is at a more favourable energy level than the resting state, but raises the puzzle of how the pump does not become stably trapped in a transport-intermediate state. We propose a model for pump allostery that includes a downhill energetic transition process from a proposed 'activated' transport state back to the resting pump.
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Affiliation(s)
- Anya Webber
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, UK; (A.W.); (A.H.)
| | - Malitha Ratnaweera
- Department of Oncology, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK;
| | - Andrzej Harris
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, UK; (A.W.); (A.H.)
| | - Ben F. Luisi
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, UK; (A.W.); (A.H.)
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6
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Alav I, Kobylka J, Kuth MS, Pos KM, Picard M, Blair JMA, Bavro VN. Structure, Assembly, and Function of Tripartite Efflux and Type 1 Secretion Systems in Gram-Negative Bacteria. Chem Rev 2021; 121:5479-5596. [PMID: 33909410 PMCID: PMC8277102 DOI: 10.1021/acs.chemrev.1c00055] [Citation(s) in RCA: 96] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Indexed: 12/11/2022]
Abstract
Tripartite efflux pumps and the related type 1 secretion systems (T1SSs) in Gram-negative organisms are diverse in function, energization, and structural organization. They form continuous conduits spanning both the inner and the outer membrane and are composed of three principal components-the energized inner membrane transporters (belonging to ABC, RND, and MFS families), the outer membrane factor channel-like proteins, and linking the two, the periplasmic adaptor proteins (PAPs), also known as the membrane fusion proteins (MFPs). In this review we summarize the recent advances in understanding of structural biology, function, and regulation of these systems, highlighting the previously undescribed role of PAPs in providing a common architectural scaffold across diverse families of transporters. Despite being built from a limited number of basic structural domains, these complexes present a staggering variety of architectures. While key insights have been derived from the RND transporter systems, a closer inspection of the operation and structural organization of different tripartite systems reveals unexpected analogies between them, including those formed around MFS- and ATP-driven transporters, suggesting that they operate around basic common principles. Based on that we are proposing a new integrated model of PAP-mediated communication within the conformational cycling of tripartite systems, which could be expanded to other types of assemblies.
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Affiliation(s)
- Ilyas Alav
- Institute
of Microbiology and Infection, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - Jessica Kobylka
- Institute
of Biochemistry, Biocenter, Goethe Universität
Frankfurt, Max-von-Laue-Straße 9, D-60438 Frankfurt, Germany
| | - Miriam S. Kuth
- Institute
of Biochemistry, Biocenter, Goethe Universität
Frankfurt, Max-von-Laue-Straße 9, D-60438 Frankfurt, Germany
| | - Klaas M. Pos
- Institute
of Biochemistry, Biocenter, Goethe Universität
Frankfurt, Max-von-Laue-Straße 9, D-60438 Frankfurt, Germany
| | - Martin Picard
- Laboratoire
de Biologie Physico-Chimique des Protéines Membranaires, CNRS
UMR 7099, Université de Paris, 75005 Paris, France
- Fondation
Edmond de Rothschild pour le développement de la recherche
Scientifique, Institut de Biologie Physico-Chimique, 75005 Paris, France
| | - Jessica M. A. Blair
- Institute
of Microbiology and Infection, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - Vassiliy N. Bavro
- School
of Life Sciences, University of Essex, Colchester, CO4 3SQ United Kingdom
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7
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Hazel AJ, Abdali N, Leus IV, Parks JM, Smith JC, Zgurskaya HI, Gumbart JC. Conformational Dynamics of AcrA Govern Multidrug Efflux Pump Assembly. ACS Infect Dis 2019; 5:1926-1935. [PMID: 31517484 DOI: 10.1021/acsinfecdis.9b00273] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Multidrug efflux pumps of pathogenic, Gram-negative bacteria comprise an innate resistance mechanism and are key contributors to the emerging global pandemic of antibiotic resistance. Several increasingly detailed cryo-electron microscopy maps have been resolved of an entire efflux pump complex, AcrAB-TolC, resulting in atomistic structural models. Using a recent model, we have carried out nearly 40 μs of molecular dynamics simulations to study one of the key components of the protein complex AcrA, the membrane fusion protein that connects the inner-membrane-bound AcrB to the outer-membrane-bound TolC. We determined a three-dimensional potential of mean force (PMF) for AcrA, which displays two main conformational basins representing assembly competent and incompetent states. Corresponding experiments show that stabilizing mutations at an interdomain interface shift the dynamic equilibrium between these states to the incompetent one, disrupting pump assembly and function and resensitizing bacteria to existing antibiotics. The modulation of AcrA dynamics through pharmacological intervention therefore presents a promising route for the development of new antibiotics.
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Affiliation(s)
- Anthony J. Hazel
- School of Physics, Georgia Institute of Technology, 837 State Street NW, Atlanta, Georgia 30332, United States
| | - Narges Abdali
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, Oklahoma 73019, United States
| | - Inga V. Leus
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, Oklahoma 73019, United States
| | - Jerry M. Parks
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
| | - Jeremy C. Smith
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831, United States
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, 1311 Cumberland Avenue, Knoxville, Tennessee 37996, United States
| | - Helen I. Zgurskaya
- Department of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, Oklahoma 73019, United States
| | - James C. Gumbart
- School of Physics, Georgia Institute of Technology, 837 State Street NW, Atlanta, Georgia 30332, United States
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8
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Darzynkiewicz ZM, Green AT, Abdali N, Hazel A, Fulton RL, Kimball J, Gryczynski Z, Gumbart JC, Parks JM, Smith JC, Zgurskaya HI. Identification of Binding Sites for Efflux Pump Inhibitors of the AcrAB-TolC Component AcrA. Biophys J 2019; 116:648-658. [PMID: 30691677 DOI: 10.1016/j.bpj.2019.01.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 01/06/2019] [Accepted: 01/07/2019] [Indexed: 01/02/2023] Open
Abstract
The overexpression of multidrug efflux pumps is an important mechanism of clinical resistance in Gram-negative bacteria. Recently, four small molecules were discovered that inhibit efflux in Escherichia coli and interact with the AcrAB-TolC efflux pump component AcrA. However, the binding site(s) for these molecules was not determined. Here, we combine ensemble docking and molecular dynamics simulations with tryptophan fluorescence spectroscopy, site-directed mutagenesis, and antibiotic susceptibility assays to probe binding sites and effects of binding of these molecules. We conclude that clorobiocin and SLU-258 likely bind at a site located between the lipoyl and β-barrel domains of AcrA.
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Affiliation(s)
| | - Adam T Green
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, Tennessee
| | - Narges Abdali
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma
| | - Anthony Hazel
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia
| | - Ronnie L Fulton
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma
| | - Joseph Kimball
- Department of Physics and Astronomy, Texas Christian University, Fort Worth, Texas
| | - Zygmunt Gryczynski
- Department of Physics and Astronomy, Texas Christian University, Fort Worth, Texas; Department of Microbiology, Immunology, and Genetics, University of North Texas Health Science Center, Fort Worth, Texas
| | - James C Gumbart
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia
| | - Jerry M Parks
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, Tennessee
| | - Jeremy C Smith
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, Tennessee; Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee
| | - Helen I Zgurskaya
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma.
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9
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Travers T, Wang KJ, López CA, Gnanakaran S. Sequence- and structure-based computational analyses of Gram-negative tripartite efflux pumps in the context of bacterial membranes. Res Microbiol 2018; 169:414-424. [DOI: 10.1016/j.resmic.2018.01.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Revised: 12/28/2017] [Accepted: 01/21/2018] [Indexed: 01/12/2023]
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10
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Vargiu AV, Ramaswamy VK, Malloci G, Malvacio I, Atzori A, Ruggerone P. Computer simulations of the activity of RND efflux pumps. Res Microbiol 2018; 169:384-392. [PMID: 29407044 DOI: 10.1016/j.resmic.2017.12.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Revised: 12/01/2017] [Accepted: 12/05/2017] [Indexed: 12/25/2022]
Abstract
The putative mechanism by which bacterial RND-type multidrug efflux pumps recognize and transport their substrates is a complex and fascinating enigma of structural biology. How a single protein can recognize a huge number of unrelated compounds and transport them through one or just a few mechanisms is an amazing feature not yet completely unveiled. The appearance of cooperativity further complicates the understanding of structure-dynamics-activity relationships in these complex machineries. Experimental techniques may have limited access to the molecular determinants and to the energetics of key processes regulating the activity of these pumps. Computer simulations are a complementary approach that can help unveil these features and inspire new experiments. Here we review recent computational studies that addressed the various molecular processes regulating the activity of RND efflux pumps.
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Affiliation(s)
- Attilio Vittorio Vargiu
- Department of Physics, University of Cagliari, Cittadella Universitaria, S.P. Monserrato-Sestu km 0.700, 09042 Monserrato (CA), Italy.
| | - Venkata Krishnan Ramaswamy
- Department of Physics, University of Cagliari, Cittadella Universitaria, S.P. Monserrato-Sestu km 0.700, 09042 Monserrato (CA), Italy
| | - Giuliano Malloci
- Department of Physics, University of Cagliari, Cittadella Universitaria, S.P. Monserrato-Sestu km 0.700, 09042 Monserrato (CA), Italy
| | - Ivana Malvacio
- Department of Physics, University of Cagliari, Cittadella Universitaria, S.P. Monserrato-Sestu km 0.700, 09042 Monserrato (CA), Italy
| | - Alessio Atzori
- Department of Physics, University of Cagliari, Cittadella Universitaria, S.P. Monserrato-Sestu km 0.700, 09042 Monserrato (CA), Italy
| | - Paolo Ruggerone
- Department of Physics, University of Cagliari, Cittadella Universitaria, S.P. Monserrato-Sestu km 0.700, 09042 Monserrato (CA), Italy.
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11
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Cacciotto P, Ramaswamy VK, Malloci G, Ruggerone P, Vargiu AV. Molecular Modeling of Multidrug Properties of Resistance Nodulation Division (RND) Transporters. Methods Mol Biol 2018; 1700:179-219. [PMID: 29177832 DOI: 10.1007/978-1-4939-7454-2_11] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Efflux pumps of the resistance nodulation division (RND) superfamily are among the major contributors to intrinsic and acquired multidrug resistance in Gram-negative bacteria. Structural information on AcrAB-TolC and MexAB-OprM, major efflux pumps of Escherichia coli and Pseudomonas aeruginosa respectively, boosted intensive research aimed at understanding the molecular mechanisms ruling the active extrusion processes. In particular, several studies were devoted to the understanding of the determinants behind the extraordinary broad specificity of the RND transporters AcrB and MexB. In this chapter, we discuss the ever-growing role computational methods have been playing in deciphering key structural and dynamical features of these transporters and of their interaction with substrates and inhibitors. We further discuss and illustrate examples from our lab of how molecular docking, homology modeling, all-atom molecular dynamics simulations and in silico free energy estimations can all together give precious insights into the processes of recognition and extrusion of substrates, as well as on the possible inhibition strategies.
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Affiliation(s)
- Pierpaolo Cacciotto
- Department of Physics, University of Cagliari, s.p. 8, 09042, Monserrato, CA, Italy
| | - Venkata K Ramaswamy
- Department of Physics, University of Cagliari, s.p. 8, 09042, Monserrato, CA, Italy
| | - Giuliano Malloci
- Department of Physics, University of Cagliari, s.p. 8, 09042, Monserrato, CA, Italy
| | - Paolo Ruggerone
- Department of Physics, University of Cagliari, s.p. 8, 09042, Monserrato, CA, Italy
| | - Attilio V Vargiu
- Department of Physics, University of Cagliari, s.p. 8, 09042, Monserrato, CA, Italy.
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12
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Zhang HY, Xu Q, Li F, Tian PC, Wang YH, Xiong Y, Zhang YH, Wei DQ. Recent progresses of simulations on passive membrane permeations in China. MOLECULAR SIMULATION 2016. [DOI: 10.1080/08927022.2015.1135333] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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13
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Dreier J, Ruggerone P. Interaction of antibacterial compounds with RND efflux pumps in Pseudomonas aeruginosa. Front Microbiol 2015; 6:660. [PMID: 26217310 PMCID: PMC4495556 DOI: 10.3389/fmicb.2015.00660] [Citation(s) in RCA: 105] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 06/16/2015] [Indexed: 01/14/2023] Open
Abstract
Pseudomonas aeruginosa infections are becoming increasingly difficult to treat due to intrinsic antibiotic resistance and the propensity of this pathogen to accumulate diverse resistance mechanisms. Hyperexpression of efflux pumps of the Resistance-Nodulation-Cell Division (RND)-type multidrug efflux pumps (e.g., MexAB-OprM), chromosomally encoded by mexAB-oprM, mexCD-oprJ, mexEF-oprN, and mexXY (-oprA) is often detected in clinical isolates and contributes to worrying multi-drug resistance phenotypes. Not all antibiotics are affected to the same extent by the aforementioned RND efflux pumps. The impact of efflux on antibiotic activity varies not only between different classes of antibiotics but also between members of the same family of antibiotics. Subtle differences in physicochemical features of compound-pump and compound-solvent interactions largely determine how compounds are affected by efflux activity. The combination of different high-resolution techniques helps to gain insight into the functioning of these molecular machineries. This review discusses substrate recognition patterns based on experimental evidence and computer simulations with a focus on MexB, the pump subunit of the main RND transporter in P. aeruginosa.
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Affiliation(s)
- Jürg Dreier
- Basilea Pharmaceutica International Ltd.,Basel, Switzerland
| | - Paolo Ruggerone
- Dipartimento di Fisica, Università di Cagliari – Cittadella UniversitariaMonserrato, Italy
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14
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Symmons MF, Marshall RL, Bavro VN. Architecture and roles of periplasmic adaptor proteins in tripartite efflux assemblies. Front Microbiol 2015; 6:513. [PMID: 26074901 PMCID: PMC4446572 DOI: 10.3389/fmicb.2015.00513] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Accepted: 05/08/2015] [Indexed: 12/12/2022] Open
Abstract
Recent years have seen major advances in the structural understanding of the different components of tripartite efflux assemblies, which encompass the multidrug efflux (MDR) pumps and type I secretion systems. The majority of these investigations have focused on the role played by the inner membrane transporters and the outer membrane factor (OMF), leaving the third component of the system – the Periplasmic Adaptor Proteins (PAPs) – relatively understudied. Here we review the current state of knowledge of these versatile proteins which, far from being passive linkers between the OMF and the transporter, emerge as active architects of tripartite assemblies, and play diverse roles in the transport process. Recognition between the PAPs and OMFs is essential for pump assembly and function, and targeting this interaction may provide a novel avenue for combating multidrug resistance. With the recent advances elucidating the drug efflux and energetics of the tripartite assemblies, the understanding of the interaction between the OMFs and PAPs is the last piece remaining in the complete structure of the tripartite pump assembly puzzle.
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Affiliation(s)
- Martyn F Symmons
- Department of Veterinary Medicine, University of Cambridge Cambridge, UK
| | - Robert L Marshall
- Institute of Microbiology and Infection, University of Birmingham Birmingham, UK
| | - Vassiliy N Bavro
- Institute of Microbiology and Infection, University of Birmingham Birmingham, UK
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15
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Zgurskaya HI, Weeks JW, Ntreh AT, Nickels LM, Wolloscheck D. Mechanism of coupling drug transport reactions located in two different membranes. Front Microbiol 2015; 6:100. [PMID: 25759685 PMCID: PMC4338810 DOI: 10.3389/fmicb.2015.00100] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Accepted: 01/26/2015] [Indexed: 01/01/2023] Open
Abstract
Gram- negative bacteria utilize a diverse array of multidrug transporters to pump toxic compounds out of the cell. Some transporters, together with periplasmic membrane fusion proteins (MFPs) and outer membrane channels, assemble trans-envelope complexes that expel multiple antibiotics across outer membranes of Gram-negative bacteria and into the external medium. Others further potentiate this efflux by pumping drugs across the inner membrane into the periplasm. Together these transporters create a powerful network of efflux that protects bacteria against a broad range of antimicrobial agents. This review is focused on the mechanism of coupling transport reactions located in two different membranes of Gram-negative bacteria. Using a combination of biochemical, genetic and biophysical approaches we have reconstructed the sequence of events leading to the assembly of trans-envelope drug efflux complexes and characterized the roles of periplasmic and outer membrane proteins in this process. Our recent data suggest a critical step in the activation of intermembrane efflux pumps, which is controlled by MFPs. We propose that the reaction cycles of transporters are tightly coupled to the assembly of the trans-envelope complexes. Transporters and MFPs exist in the inner membrane as dormant complexes. The activation of complexes is triggered by MFP binding to the outer membrane channel, which leads to a conformational change in the membrane proximal domain of MFP needed for stimulation of transporters. The activated MFP-transporter complex engages the outer membrane channel to expel substrates across the outer membrane. The recruitment of the channel is likely triggered by binding of effectors (substrates) to MFP or MFP-transporter complexes. This model together with recent structural and functional advances in the field of drug efflux provides a fairly detailed understanding of the mechanism of drug efflux across the two membranes.
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Affiliation(s)
- Helen I Zgurskaya
- Department of Chemistry and Biochemistry, University of Oklahoma Norman, OK, USA
| | - Jon W Weeks
- Department of Chemistry and Biochemistry, University of Oklahoma Norman, OK, USA
| | - Abigail T Ntreh
- Department of Chemistry and Biochemistry, University of Oklahoma Norman, OK, USA
| | - Logan M Nickels
- Department of Chemistry and Biochemistry, University of Oklahoma Norman, OK, USA
| | - David Wolloscheck
- Department of Chemistry and Biochemistry, University of Oklahoma Norman, OK, USA
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16
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Computational study of correlated domain motions in the AcrB efflux transporter. BIOMED RESEARCH INTERNATIONAL 2015; 2015:487298. [PMID: 25685792 PMCID: PMC4313061 DOI: 10.1155/2015/487298] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 10/09/2014] [Accepted: 10/23/2014] [Indexed: 12/14/2022]
Abstract
As active part of the major efflux system in E. coli bacteria, AcrB is responsible for the uptake and pumping of toxic substrates from the periplasm toward the extracellular space. In combination with the channel protein TolC and membrane fusion protein AcrA, this efflux pump is able to help the bacterium to survive different kinds of noxious compounds. With the present study we intend to enhance the understanding of the interactions between the domains and monomers, for example, the transduction of mechanical energy from the transmembrane domain into the porter domain, correlated motions of different subdomains within monomers, and cooperative effects between monomers. To this end, targeted molecular dynamics simulations have been employed either steering the whole protein complex or specific parts thereof. By forcing only parts of the complex towards specific conformational states, the risk for transient artificial conformations during the simulations is reduced. Distinct cooperative effects between the monomers in AcrB have been observed. Possible allosteric couplings have been identified providing microscopic insights that might be exploited to design more efficient inhibitors of efflux systems.
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17
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Wang B, Weng J, Wang W. Multiple conformational states and gate opening of outer membrane protein TolC revealed by molecular dynamics simulations. Proteins 2014; 82:2169-79. [DOI: 10.1002/prot.24573] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 03/12/2014] [Accepted: 03/29/2014] [Indexed: 11/07/2022]
Affiliation(s)
- Beibei Wang
- Department of Chemistry; Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University; Shanghai People's Republic of China
| | - Jingwei Weng
- Department of Chemistry; Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University; Shanghai People's Republic of China
| | - Wenning Wang
- Department of Chemistry; Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University; Shanghai People's Republic of China
- Institutes of Biomedical Sciences, Fudan University; Shanghai People's Republic of China
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18
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Lee S, Song S, Lee M, Hwang S, Kim JS, Ha NC, Lee K. Interaction between the α-barrel tip of Vibrio vulnificus TolC homologs and AcrA implies the adapter bridging model. J Microbiol 2014; 52:148-53. [PMID: 24500479 DOI: 10.1007/s12275-014-3578-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Revised: 12/05/2013] [Accepted: 12/06/2013] [Indexed: 10/25/2022]
Abstract
The AcrAB-TolC multidrug efflux pump confers resistance to Escherichia coli against many antibiotics and toxic compounds. The TolC protein is an outer membrane factor that participates in the formation of type I secretion systems. The genome of Vibrio vulnificus encodes two proteins homologous to the E. coli TolC, designated TolCV1 and TolCV2. Here, we show that both TolCV1 and TolCV2 partially complement the E. coli TolC function and physically interact with the membrane fusion protein AcrA, a component of the E. coli AcrAB-TolC efflux pump. Using site-directed mutational analyses and an in vivo cross-linking assay, we demonstrated that the α-barrel tip region of TolC homologs plays a critical role in the formation of functional AcrAB-TolC efflux pumps. Our findings suggest the adapter bridging model as a general assembly mechanism for tripartite drug efflux pumps in Gram-negative bacteria.
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Affiliation(s)
- Seunghwa Lee
- Department of Life Science, Chung-Ang University, Seoul, 156-756, Republic of Korea
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19
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Fischer N, Raunest M, Schmidt TH, Koch DC, Kandt C. Efflux pump-mediated antibiotics resistance: Insights from computational structural biology. Interdiscip Sci 2014; 6:1-12. [DOI: 10.1007/s12539-014-0191-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2013] [Revised: 09/03/2013] [Accepted: 11/18/2013] [Indexed: 01/08/2023]
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20
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Yao XQ, Kimura N, Murakami S, Takada S. Drug uptake pathways of multidrug transporter AcrB studied by molecular simulations and site-directed mutagenesis experiments. J Am Chem Soc 2013; 135:7474-85. [PMID: 23627437 DOI: 10.1021/ja310548h] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Multidrug resistance has been a critical issue in current chemotherapy. In Escherichia coli , a major efflux pump responsible for the multidrug resistance contains a transporter AcrB. Crystallographic studies and mutational assays of AcrB provided much of structural and overall functional insights, which led to the functionally rotating mechanism. However, the drug uptake pathways are somewhat controversial because at least two possible pathways, the vestibule and the cleft paths, were suggested. Here, combining molecular simulations and site-directed mutagenesis experiments, we addressed the uptake mechanism finding that the drug uptake pathways can be significantly different depending on the properties of drugs. First, in the computational free energy analysis of drug movements along AcrB tunnels, we found a ligand-dependent drug uptake mechanism. With the same molecular sizes, drugs that are both strongly hydrophobic and lipophilic were preferentially taken in via the vestibule path, while other drugs favored the cleft path. Second, direct simulations realized totally about 3500 events of drug uptake by AcrB for a broad range of drug property. These simulations confirmed the ligand-dependent drug uptake and further suggested that a smaller drug favors the vestibule path, while a larger one is taken in via the cleft path. Moreover, the direct simulations identified an alternative uptake path which is not visible in the crystal structure. Third, site-directed mutagenesis of AcrB in E. coli verified that mutations of residues located along the newly identified path significantly reduced the efflux efficiency, supporting its relevance in in vivo function.
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Affiliation(s)
- Xin-Qiu Yao
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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21
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Janganan TK, Bavro VN, Zhang L, Borges-Walmsley MI, Walmsley AR. Tripartite efflux pumps: energy is required for dissociation, but not assembly or opening of the outer membrane channel of the pump. Mol Microbiol 2013; 88:590-602. [PMID: 23565750 PMCID: PMC3664412 DOI: 10.1111/mmi.12211] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/19/2013] [Indexed: 11/26/2022]
Abstract
The MtrCDE multidrug pump, from Neisseria gonorrhoeae, is assembled from the inner and outer membrane proteins MtrD and MtrE, which are connected by the periplasmic membrane fusion protein MtrC. Although it is clear that MtrD delivers drugs to the channel of MtrE, it remains unclear how drug delivery and channel opening are connected. We used a vancomycin sensitivity assay to test for opening of the MtrE channel. Cells expressing MtrE or MtrE-E434K were insensitive to vancomycin; but became moderately and highly sensitive to vancomycin respectively, when coexpressed with MtrC, suggesting that the MtrE channel opening requires MtrC binding and is energy-independent. Cells expressing wild-type MtrD, in an MtrCE background, were vancomycin-insensitive, but moderately sensitive in an MtrCE-E434K background. The mutation of residues involved in proton translocation inactivated MtrD and abolished drug efflux, rendered both MtrE and MtrE-E434K vancomycin-insensitive; imply that the pump-component interactions are preserved, and that the complex is stable in the absence of proton flux, thus sealing the open end of MtrE. Following the energy-dependent dissociation of the tripartite complex, the MtrE channel is able to reseal, while MtrE-E434K is unable to do so, resulting in the vancomycin-sensitive phenotype. Thus, our findings suggest that opening of the OMP via interaction with the MFP is energy-independent, while both drug export and complex dissociation require active proton flux.
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Affiliation(s)
- Thamarai K Janganan
- School of Biological and Biomedical Sciences, Durham University, South Road, Durham, DH1 3LE, UK
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22
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Ruggerone P, Vargiu AV, Collu F, Fischer N, Kandt C. Molecular Dynamics Computer Simulations of Multidrug RND Efflux Pumps. Comput Struct Biotechnol J 2013; 5:e201302008. [PMID: 24688701 PMCID: PMC3962194 DOI: 10.5936/csbj.201302008] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Revised: 01/31/2013] [Accepted: 02/04/2013] [Indexed: 01/13/2023] Open
Abstract
Over-expression of multidrug efflux pumps of the Resistance Nodulation Division (RND) protein super family counts among the main causes for microbial resistance against pharmaceuticals. Understanding the molecular basis of this process is one of the major challenges of modern biomedical research, involving a broad range of experimental and computational techniques. Here we review the current state of RND transporter investigation employing molecular dynamics simulations providing conformational samples of transporter components to obtain insights into the functional mechanism underlying efflux pump-mediated antibiotics resistance in Escherichia coli and Pseudomonas aeruginosa.
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Affiliation(s)
- Paolo Ruggerone
- Department of Physics, University of Cagliari, Cittadella Universitaria S.P. Monserrato-Sestu Km 0.700, 09042 Monserrato (CA), Cagliari, Italy ; CNR-IOM, Unità SLACS, S.P. Monserrato-Sestu Km 0.700, I-09042 Monserrato (CA), Italy
| | - Attilio V Vargiu
- Department of Physics, University of Cagliari, Cittadella Universitaria S.P. Monserrato-Sestu Km 0.700, 09042 Monserrato (CA), Cagliari, Italy ; CNR-IOM, Unità SLACS, S.P. Monserrato-Sestu Km 0.700, I-09042 Monserrato (CA), Italy
| | - Francesca Collu
- Departement fu r Chemie und Biochemie, Universita t Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
| | - Nadine Fischer
- Computational Structural Biology, Department of Life Science Informatics B-IT, Life & Medical Sciences Institute, University of Bonn, Dahlmannstr. 2, 53113 Bonn, Germany
| | - Christian Kandt
- Computational Structural Biology, Department of Life Science Informatics B-IT, Life & Medical Sciences Institute, University of Bonn, Dahlmannstr. 2, 53113 Bonn, Germany
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23
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Mealman TD, Blackburn NJ, McEvoy MM. Metal export by CusCFBA, the periplasmic Cu(I)/Ag(I) transport system of Escherichia coli. CURRENT TOPICS IN MEMBRANES 2012; 69:163-96. [PMID: 23046651 DOI: 10.1016/b978-0-12-394390-3.00007-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
High levels of metal ions have the potential to cause cellular toxicity through a variety of mechanisms; therefore, cells have developed numerous systems that regulate their intracellular concentrations. The Cus resistance system aids in protection of Escherichia coli from high levels of Cu(I) and Ag(I) by actively transporting these metal ions to the extracellular environment. The Cus system forms a continuous complex, CusCBA, that spans the inner membrane, periplasm, and outer membrane of Gram-negative bacteria, together with a novel fourth component, the periplasmic metallochaperone, CusF. The metal-binding sites of CusA, CusB, and CusF are exquisitely tuned for Cu(I) and Ag(I), and thus effectively discriminate these ions for transport from other metals that may be required in the cell. Furthermore, direct transfer of metal from protein to protein within the Cus system during the transport process is likely to reduce the potential toxicity posed by the free metal ions. Here we review the wealth of structural, biochemical, and genetic information on the Cus system, which demonstrates the many intriguing aspects of function for metal-transporting efflux systems.
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Affiliation(s)
- Tiffany D Mealman
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ, USA
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