51
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Hürlimann LM, Corradi V, Hohl M, Bloemberg GV, Tieleman DP, Seeger MA. The Heterodimeric ABC Transporter EfrCD Mediates Multidrug Efflux in Enterococcus faecalis. Antimicrob Agents Chemother 2016; 60:5400-11. [PMID: 27381387 PMCID: PMC4997860 DOI: 10.1128/aac.00661-16] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Accepted: 06/20/2016] [Indexed: 11/22/2022] Open
Abstract
Nosocomial infections with Enterococcus faecalis are an emerging health problem. However, drug efflux pumps contributing to intrinsic drug resistance are poorly studied in this Gram-positive pathogen. In this study, we functionally investigated seven heterodimeric ABC transporters of E. faecalis that are annotated as drug efflux pumps. Deletion of ef0789-ef0790 on the chromosome of E. faecalis resulted in increased susceptibility to daunorubicin, doxorubicin, ethidium, and Hoechst 33342, and the corresponding transporter was named EfrCD. Unexpectedly, the previously described heterodimeric multidrug ABC transporter EfrAB contributes marginally to drug efflux in the endogenous context of E. faecalis In contrast, heterologous expression in Lactococcus lactis revealed that EfrAB, EfrCD, and the product of ef2226-ef2227 (EfrEF) mediate the efflux of fluorescent substrates and confer resistance to multiple dyes and drugs, including fluoroquinolones. Four of seven transporters failed to exhibit drug efflux activity for the set of drugs and dyes tested, even upon overexpression in L. lactis Since all seven transporters were purified as heterodimers after overexpression in L. lactis, a lack of drug efflux activity is not attributed to poor expression or protein aggregation. Reconstitution of the purified multidrug transporters EfrAB, EfrCD, and EfrEF in proteoliposomes revealed functional coupling between ATP hydrolysis and drug binding. Our analysis creates an experimental basis for the accurate prediction of drug efflux transporters and indicates that many annotated multidrug efflux pumps might be incapable of drug transport and thus might fulfill other physiological functions in the cell.
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Affiliation(s)
- Lea M Hürlimann
- Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
| | - Valentina Corradi
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Michael Hohl
- Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
| | - Guido V Bloemberg
- Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
| | - D Peter Tieleman
- Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Markus A Seeger
- Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
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52
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Zhou Y, Ojeda-May P, Nagaraju M, Pu J. Toward Determining ATPase Mechanism in ABC Transporters: Development of the Reaction Path-Force Matching QM/MM Method. Methods Enzymol 2016; 577:185-212. [PMID: 27498639 PMCID: PMC4985252 DOI: 10.1016/bs.mie.2016.05.054] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Adenosine triphosphate (ATP)-binding cassette (ABC) transporters are ubiquitous ATP-dependent membrane proteins involved in translocations of a wide variety of substrates across cellular membranes. To understand the chemomechanical coupling mechanism as well as functional asymmetry in these systems, a quantitative description of how ABC transporters hydrolyze ATP is needed. Complementary to experimental approaches, computer simulations based on combined quantum mechanical and molecular mechanical (QM/MM) potentials have provided new insights into the catalytic mechanism in ABC transporters. Quantitatively reliable determination of the free energy requirement for enzymatic ATP hydrolysis, however, requires substantial statistical sampling on QM/MM potential. A case study shows that brute force sampling of ab initio QM/MM (AI/MM) potential energy surfaces is computationally impractical for enzyme simulations of ABC transporters. On the other hand, existing semiempirical QM/MM (SE/MM) methods, although affordable for free energy sampling, are unreliable for studying ATP hydrolysis. To close this gap, a multiscale QM/MM approach named reaction path-force matching (RP-FM) has been developed. In RP-FM, specific reaction parameters for a selected SE method are optimized against AI reference data along reaction paths by employing the force matching technique. The feasibility of the method is demonstrated for a proton transfer reaction in the gas phase and in solution. The RP-FM method may offer a general tool for simulating complex enzyme systems such as ABC transporters.
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Affiliation(s)
- Y Zhou
- Indiana University-Purdue University Indianapolis, Indianapolis, IN, United States
| | - P Ojeda-May
- Indiana University-Purdue University Indianapolis, Indianapolis, IN, United States
| | - M Nagaraju
- Indiana University-Purdue University Indianapolis, Indianapolis, IN, United States
| | - J Pu
- Indiana University-Purdue University Indianapolis, Indianapolis, IN, United States.
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53
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Chaves LAP, Gadsby DC. Cysteine accessibility probes timing and extent of NBD separation along the dimer interface in gating CFTR channels. ACTA ACUST UNITED AC 2015; 145:261-83. [PMID: 25825169 PMCID: PMC4380215 DOI: 10.1085/jgp.201411347] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) channel opening and closing are driven by cycles of adenosine triphosphate (ATP) binding-induced formation and hydrolysis-triggered disruption of a heterodimer of its cytoplasmic nucleotide-binding domains (NBDs). Although both composite sites enclosed within the heterodimer interface contain ATP in an open CFTR channel, ATP hydrolysis in the sole catalytically competent site causes channel closure. Opening of the NBD interface at that site then allows ADP-ATP exchange. But how frequently, and how far, the NBD surfaces separate at the other, inactive composite site remains unclear. We assessed separation at each composite site by monitoring access of nucleotide-sized hydrophilic, thiol-specific methanothiosulfonate (MTS) reagents to interfacial target cysteines introduced into either LSGGQ-like ATP-binding cassette signature sequence (replacing equivalent conserved serines: S549 and S1347). Covalent MTS-dependent modification of either cysteine while channels were kept closed by the absence of ATP impaired subsequent opening upon ATP readdition. Modification while channels were opening and closing in the presence of ATP caused macroscopic CFTR current to decline at the same speed as when the unmodified channels shut upon sudden ATP withdrawal. These results suggest that the target cysteines can be modified only in closed channels; that after modification the attached MTS adduct interferes with ATP-mediated opening; and that modification in the presence of ATP occurs rapidly once channels close, before they can reopen. This interpretation was corroborated by the finding that, for either cysteine target, the addition of the hydrolysis-impairing mutation K1250R (catalytic site Walker A Lys) similarly slowed, by an order of magnitude, channel closing on ATP removal and the speed of modification by MTS reagent in ATP. We conclude that, in every CFTR channel gating cycle, the NBD dimer interface separates simultaneously at both composite sites sufficiently to allow MTS reagents to access both signature-sequence serines. Relatively rapid modification of S1347C channels by larger reagents-MTS-glucose, MTS-biotin, and MTS-rhodamine-demonstrates that, at the noncatalytic composite site, this separation must exceed 8 Å.
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Affiliation(s)
- Luiz A Poletto Chaves
- The Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, NY 10065
| | - David C Gadsby
- The Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, NY 10065
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54
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Geng J, Pogozheva ID, Mosberg HI, Raghavan M. Use of Functional Polymorphisms To Elucidate the Peptide Binding Site of TAP Complexes. THE JOURNAL OF IMMUNOLOGY 2015; 195:3436-48. [PMID: 26324772 DOI: 10.4049/jimmunol.1500985] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2015] [Accepted: 07/29/2015] [Indexed: 11/19/2022]
Abstract
TAP1/TAP2 complexes translocate peptides from the cytosol to the endoplasmic reticulum lumen to enable immune surveillance by CD8(+) T cells. Peptide transport is preceded by peptide binding to a cytosol-accessible surface of TAP1/TAP2 complexes, but the location of the TAP peptide-binding pocket remains unknown. Guided by the known contributions of polymorphic TAP variants to peptide selection, we combined homology modeling of TAP with experimental measurements to identify several TAP residues that interact with peptides. Models for peptide-TAP complexes were generated, which indicate bent conformation for peptides. The peptide binding site of TAP is located at the hydrophobic boundary of the cytosolic membrane leaflet, with striking parallels to the glutathione binding site of NaAtm1, a transporter that functions in bacterial heavy metal detoxification. These studies illustrate the conservation of the ligand recognition modes of bacterial and mammalians transporters involved in peptide-guided cellular surveillance.
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Affiliation(s)
- Jie Geng
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109; and
| | - Irina D Pogozheva
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan Medical School, Ann Arbor, MI 48109
| | - Henry I Mosberg
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan Medical School, Ann Arbor, MI 48109
| | - Malini Raghavan
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109; and
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55
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Bukowska MA, Hohl M, Geertsma ER, Hürlimann LM, Grütter MG, Seeger MA. A Transporter Motor Taken Apart: Flexibility in the Nucleotide Binding Domains of a Heterodimeric ABC Exporter. Biochemistry 2015; 54:3086-99. [PMID: 25947941 DOI: 10.1021/acs.biochem.5b00188] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
ABC exporters are ubiquitous multidomain transport proteins that couple ATP hydrolysis at a pair of nucleotide binding domains to substrate transport across the lipid bilayer mediated by two transmembrane domains. Recently, the crystal structure of the heterodimeric ABC exporter TM287/288 was determined. One of its asymmetric ATP binding sites is called the degenerate site; it binds nucleotides tightly but is impaired in terms of ATP hydrolysis. Here we report the crystal structures of both isolated motor domains of TM287/288. Unexpectedly, structural elements constituting the degenerate ATP binding site are disordered in these crystals and become structured only in the context of the full-length transporter. In addition, hydrogen bonding patterns of key residues, including those of the catalytically important Walker B and the switch loop motifs, are fundamentally different in the solitary NBDs compared to those in the intact transport protein. The structures reveal crucial interdomain contacts that need to be established for the proper assembly of the functional transporter complex.
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Affiliation(s)
- Magdalena A Bukowska
- †Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Michael Hohl
- †Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.,‡Institute of Medical Microbiology, University of Zurich, Gloriastrasse 30/32, 8006 Zurich, Switzerland
| | - Eric R Geertsma
- †Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Lea M Hürlimann
- †Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.,‡Institute of Medical Microbiology, University of Zurich, Gloriastrasse 30/32, 8006 Zurich, Switzerland
| | - Markus G Grütter
- †Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Markus A Seeger
- †Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.,‡Institute of Medical Microbiology, University of Zurich, Gloriastrasse 30/32, 8006 Zurich, Switzerland
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56
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Golin J, Ambudkar SV. The multidrug transporter Pdr5 on the 25th anniversary of its discovery: an important model for the study of asymmetric ABC transporters. Biochem J 2015; 467:353-63. [PMID: 25886173 PMCID: PMC4784962 DOI: 10.1042/bj20150042] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Asymmetric ABC (ATP-binding cassette) transporters make up a significant proportion of this important superfamily of integral membrane proteins. These proteins contain one canonical (catalytic) ATP-binding site and a second atypical site with little enzymatic capability. The baker's yeast (Saccharomyces cerevisiae) Pdr5 multidrug transporter is the founding member of the Pdr subfamily of asymmetric ABC transporters, which exist only in fungi and slime moulds. Because these organisms are of considerable medical and agricultural significance, Pdr5 has been studied extensively, as has its medically important homologue Cdr1 from Candida albicans. Genetic and biochemical analyses of Pdr5 have contributed important observations that are likely to be applicable to mammalian asymmetric ABC multidrug transporter proteins, including the basis of transporter promiscuity, the function of the non-catalytic deviant ATP-binding site, the most complete description of an in vivo transmission interface, and the recent discovery that Pdr5 is a molecular diode (one-way gate). In the present review, we discuss the observations made with Pdr5 and compare them with findings from clinically important asymmetric ABC transporters, such as CFTR (cystic fibrosis transmembrane conductance regulator), Cdr1 and Tap1/Tap2.
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Affiliation(s)
- John Golin
- Department of Biology, The Catholic University of America, Washington, DC 20064, U.S.A
| | - Suresh V. Ambudkar
- The Laboratory of Cell Biology, Center for Cancer Research, NCI, NIH, Bethesda, MD 20892, U.S.A
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57
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Verweij MC, Horst D, Griffin BD, Luteijn RD, Davison AJ, Ressing ME, Wiertz EJHJ. Viral inhibition of the transporter associated with antigen processing (TAP): a striking example of functional convergent evolution. PLoS Pathog 2015; 11:e1004743. [PMID: 25880312 PMCID: PMC4399834 DOI: 10.1371/journal.ppat.1004743] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Herpesviruses are large DNA viruses that are highly abundant within their host populations. Even in the presence of a healthy immune system, these viruses manage to cause lifelong infections. This persistence is partially mediated by the virus entering latency, a phase of infection characterized by limited viral protein expression. Moreover, herpesviruses have devoted a significant part of their coding capacity to immune evasion strategies. It is believed that the close coexistence of herpesviruses and their hosts has resulted in the evolution of viral proteins that specifically attack multiple arms of the host immune system. Cytotoxic T lymphocytes (CTLs) play an important role in antiviral immunity. CTLs recognize their target through viral peptides presented in the context of MHC molecules at the cell surface. Every herpesvirus studied to date encodes multiple immune evasion molecules that effectively interfere with specific steps of the MHC class I antigen presentation pathway. The transporter associated with antigen processing (TAP) plays a key role in the loading of viral peptides onto MHC class I molecules. This is reflected by the numerous ways herpesviruses have developed to block TAP function. In this review, we describe the characteristics and mechanisms of action of all known virus-encoded TAP inhibitors. Orthologs of these proteins encoded by related viruses are identified, and the conservation of TAP inhibition is discussed. A phylogenetic analysis of members of the family Herpesviridae is included to study the origin of these molecules. In addition, we discuss the characteristics of the first TAP inhibitor identified outside the herpesvirus family, namely, in cowpox virus. The strategies of TAP inhibition employed by viruses are very distinct and are likely to have been acquired independently during evolution. These findings and the recent discovery of a non-herpesvirus TAP inhibitor represent a striking example of functional convergent evolution.
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Affiliation(s)
- Marieke C. Verweij
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Daniëlle Horst
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Bryan D. Griffin
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Rutger D. Luteijn
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Andrew J. Davison
- MRC—University of Glasgow Centre for Virus Research, Glasgow, United Kingdom
| | - Maaike E. Ressing
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Emmanuel J. H. J. Wiertz
- Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands
- * E-mail:
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58
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Clifton MC, Simon MJ, Erramilli SK, Zhang H, Zaitseva J, Hermodson MA, Stauffacher CV. In vitro reassembly of the ribose ATP-binding cassette transporter reveals a distinct set of transport complexes. J Biol Chem 2014; 290:5555-65. [PMID: 25533465 DOI: 10.1074/jbc.m114.621573] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Bacterial ATP-binding cassette (ABC) importers are primary active transporters that are critical for nutrient uptake. Based on structural and functional studies, ABC importers can be divided into two distinct classes, type I and type II. Type I importers follow a strict alternating access mechanism that is driven by the presence of the substrate. Type II importers accept substrates in a nucleotide-free state, with hydrolysis driving an inward facing conformation. The ribose transporter in Escherichia coli is a tripartite complex consisting of a cytoplasmic ATP-binding cassette protein, RbsA, with fused nucleotide binding domains; a transmembrane domain homodimer, RbsC2; and a periplasmic substrate binding protein, RbsB. To investigate the transport mechanism of the complex RbsABC2, we probed intersubunit interactions by varying the presence of the substrate ribose and the hydrolysis cofactors, ATP/ADP and Mg(2+). We were able to purify a full complex, RbsABC2, in the presence of stable, transition state mimics (ATP, Mg(2+), and VO4); a RbsAC complex in the presence of ADP and Mg(2+); and a heretofore unobserved RbsBC complex in the absence of cofactors. The presence of excess ribose also destabilized complex formation between RbsB and RbsC. These observations suggest that RbsABC2 shares functional traits with both type I and type II importers, as well as possessing unique features, and employs a distinct mechanism relative to other ABC transporters.
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Affiliation(s)
- Matthew C Clifton
- From the Department of Biological Sciences and the Purdue Center for Cancer Research and
| | - Michael J Simon
- From the Department of Biological Sciences and the Purdue Center for Cancer Research and
| | - Satchal K Erramilli
- From the Department of Biological Sciences and the Purdue Center for Cancer Research and
| | - Huide Zhang
- the Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
| | - Jelena Zaitseva
- the Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
| | - Mark A Hermodson
- the Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
| | - Cynthia V Stauffacher
- From the Department of Biological Sciences and the Purdue Center for Cancer Research and
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59
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Mechanistic determinants of the directionality and energetics of active export by a heterodimeric ABC transporter. Nat Commun 2014; 5:5419. [PMID: 25377891 PMCID: PMC4242082 DOI: 10.1038/ncomms6419] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Accepted: 09/29/2014] [Indexed: 11/09/2022] Open
Abstract
The ATP-binding cassette (ABC) transporter associated with antigen processing (TAP) participates in immune surveillance by moving proteasomal products into the endoplasmic reticulum (ER) lumen for major histocompatibility complex class I loading and cell surface presentation to cytotoxic T cells. Here we delineate the mechanistic basis for antigen translocation. Notably, TAP works as a molecular diode, translocating peptide substrates against the gradient in a strict unidirectional way. We reveal the importance of the D-loop at the dimer interface of the two nucleotide-binding domains (NBDs) in coupling substrate translocation with ATP hydrolysis and defining transport vectoriality. Substitution of the conserved aspartate, which coordinates the ATP-binding site, decreases NBD dimerization affinity and turns the unidirectional primary active pump into a passive bidirectional nucleotide-gated facilitator. Thus, ATP hydrolysis is not required for translocation per se, but is essential for both active and unidirectional transport. Our data provide detailed mechanistic insight into how heterodimeric ABC exporters operate.
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60
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de Marcos Lousa C, Dietrich D, Johnson B, Baldwin S, Holdsworth M, Theodoulou FL, Baker A. The NBDs that wouldn't die. Commun Integr Biol 2014. [DOI: 10.4161/cib.7621] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
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61
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Hinz A, Jedamzick J, Herbring V, Fischbach H, Hartmann J, Parcej D, Koch J, Tampé R. Assembly and function of the major histocompatibility complex (MHC) I peptide-loading complex are conserved across higher vertebrates. J Biol Chem 2014; 289:33109-17. [PMID: 25320083 DOI: 10.1074/jbc.m114.609263] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Antigen presentation to cytotoxic T lymphocytes via major histocompatibility complex class I (MHC I) molecules depends on the heterodimeric transporter associated with antigen processing (TAP). For efficient antigen supply to MHC I molecules in the ER, TAP assembles a macromolecular peptide-loading complex (PLC) by recruiting tapasin. In evolution, TAP appeared together with effector cells of adaptive immunity at the transition from jawless to jawed vertebrates and diversified further within the jawed vertebrates. Here, we compared TAP function and interaction with tapasin of a range of species within two classes of jawed vertebrates. We found that avian and mammalian TAP1 and TAP2 form heterodimeric complexes across taxa. Moreover, the extra N-terminal domain TMD0 of mammalian TAP1 and TAP2 as well as avian TAP2 recruits tapasin. Strikingly, however, only TAP1 and TAP2 from the same taxon can form a functional heterodimeric translocation complex. These data demonstrate that the dimerization interface between TAP1 and TAP2 and the tapasin docking sites for PLC assembly are conserved in evolution, whereas elements of antigen translocation diverged later in evolution and are thus taxon specific.
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Affiliation(s)
- Andreas Hinz
- From the Institute of Biochemistry, Biocenter and
| | | | | | | | - Jessica Hartmann
- Georg-Speyer-Haus, Institute for Tumor Biology and Experimental Therapy, Paul-Ehrlich-Str. 42, 60596 Frankfurt/M., Germany
| | - David Parcej
- From the Institute of Biochemistry, Biocenter and
| | - Joachim Koch
- Georg-Speyer-Haus, Institute for Tumor Biology and Experimental Therapy, Paul-Ehrlich-Str. 42, 60596 Frankfurt/M., Germany
| | - Robert Tampé
- From the Institute of Biochemistry, Biocenter and Cluster of Excellence-Macromolecular Complexes, Goethe-University, Max-von-Laue-Str. 9, 60438 Frankfurt/M., Germany and
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62
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ABC transporters in adaptive immunity. Biochim Biophys Acta Gen Subj 2014; 1850:449-60. [PMID: 24923865 DOI: 10.1016/j.bbagen.2014.05.022] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2014] [Revised: 05/24/2014] [Accepted: 05/29/2014] [Indexed: 12/12/2022]
Abstract
BACKGROUND ABC transporters ubiquitously found in all kingdoms of life move a broad range of solutes across membranes. Crystal structures of four distinct types of ABC transport systems have been solved, shedding light on different conformational states within the transport process. Briefly, ATP-dependent flipping between inward- and outward-facing conformations allows directional transport of various solutes. SCOPE OF REVIEW The heterodimeric transporter associated with antigen processing TAP1/2 (ABCB2/3) is a crucial element of the adaptive immune system. The ABC transport complex shuttles proteasomal degradation products into the endoplasmic reticulum. These antigenic peptides are loaded onto major histocompatibility complex class I molecules and presented on the cell surface. We detail the functional modules of TAP, its ATPase and transport cycle, and its interaction with and modulation by other cellular components. In particular, we emphasize how viral factors inhibit TAP activity and thereby prevent detection of the infected host cell by cytotoxic T-cells. MAJOR CONCLUSIONS Merging functional details on TAP with structural insights from related ABC transporters refines the understanding of solute transport. Although human ABC transporters are extremely diverse, they still may employ conceptually related transport mechanisms. Appropriately, we delineate a working model of the transport cycle and how viral factors arrest TAP in distinct conformations. GENERAL SIGNIFICANCE Deciphering the transport cycle of human ABC proteins is the major issue in the field. The defined peptidic substrate, various inhibitory viral factors, and its role in adaptive immunity provide unique tools for the investigation of TAP, making it an ideal model system for ABC transporters in general. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.
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63
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Mishra S, Verhalen B, Stein RA, Wen PC, Tajkhorshid E, Mchaourab HS. Conformational dynamics of the nucleotide binding domains and the power stroke of a heterodimeric ABC transporter. eLife 2014; 3:e02740. [PMID: 24837547 PMCID: PMC4046567 DOI: 10.7554/elife.02740] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Multidrug ATP binding cassette (ABC) exporters are ubiquitous ABC transporters that extrude cytotoxic molecules across cell membranes. Despite recent progress in structure determination of these transporters, the conformational motion that transduces the energy of ATP hydrolysis to the work of substrate translocation remains undefined. Here, we have investigated the conformational cycle of BmrCD, a representative of the heterodimer family of ABC exporters that have an intrinsically impaired nucleotide binding site. We measured distances between pairs of spin labels monitoring the movement of the nucleotide binding (NBD) and transmembrane domains (TMD). The results expose previously unobserved structural intermediates of the NBDs arising from asymmetric configuration of catalytically inequivalent nucleotide binding sites. The two-state transition of the TMD, from an inward- to an outward-facing conformation, is driven exclusively by ATP hydrolysis. These findings provide direct evidence of divergence in the mechanism of ABC exporters.DOI: http://dx.doi.org/10.7554/eLife.02740.001.
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Affiliation(s)
- Smriti Mishra
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
| | - Brandy Verhalen
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
| | - Richard A Stein
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
| | - Po-Chao Wen
- Department of Biochemistry, College of Medicine, University of Illinois, Urbana, United States Center for Biophysics and Computational Biology, University of Illinois, Urbana, United States The Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Unites States
| | - Emad Tajkhorshid
- Department of Biochemistry, College of Medicine, University of Illinois, Urbana, United States Center for Biophysics and Computational Biology, University of Illinois, Urbana, United States The Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Unites States
| | - Hassane S Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
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64
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Structure and mechanism of ATP-dependent phospholipid transporters. Biochim Biophys Acta Gen Subj 2014; 1850:461-75. [PMID: 24746984 DOI: 10.1016/j.bbagen.2014.04.008] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2014] [Revised: 04/04/2014] [Accepted: 04/07/2014] [Indexed: 01/09/2023]
Abstract
BACKGROUND ATP-binding cassette (ABC) transporters and P4-ATPases are two large and seemingly unrelated families of primary active pumps involved in moving phospholipids from one leaflet of a biological membrane to the other. SCOPE OF REVIEW This review aims to identify common mechanistic features in the way phospholipid flipping is carried out by two evolutionarily unrelated families of transporters. MAJOR CONCLUSIONS Both protein families hydrolyze ATP, although they employ different mechanisms to use it, and have a comparable size with twelve transmembrane segments in the functional unit. Further, despite differences in overall architecture, both appear to operate by an alternating access mechanism and during transport they might allow access of phospholipids to the internal part of the transmembrane domain. The latter feature is obvious for ABC transporters, but phospholipids and other hydrophobic molecules have also been found embedded in P-type ATPase crystal structures. Taken together, in two diverse groups of pumps, nature appears to have evolved quite similar ways of flipping phospholipids. GENERAL SIGNIFICANCE Our understanding of the structural basis for phospholipid flipping is still limited but it seems plausible that a general mechanism for phospholipid flipping exists in nature. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.
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65
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Geng J, Sivaramakrishnan S, Raghavan M. Analyses of conformational states of the transporter associated with antigen processing (TAP) protein in a native cellular membrane environment. J Biol Chem 2013; 288:37039-47. [PMID: 24196954 DOI: 10.1074/jbc.m113.504696] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The transporter associated with antigen processing (TAP) plays a critical role in the MHC class I antigen presentation pathway. TAP translocates cellular peptides across the endoplasmic reticulum membrane in an ATP hydrolysis-dependent manner. We used FRET spectroscopy in permeabilized cells to delineate different conformational states of TAP in a native subcellular membrane environment. For these studies, we tagged the TAP1 and TAP2 subunits with enhanced cyan fluorescent protein and enhanced yellow fluorescent protein, respectively, C-terminally to their nucleotide binding domains (NBDs), and measured FRET efficiencies under different conditions. Our data indicate that both ATP and ADP enhance the FRET efficiencies but that neither induces a maximally closed NBD conformation. Additionally, peptide binding induces a large and significant increase in NBD proximity with a concentration dependence that is reflective of individual peptide affinities for TAP, revealing the underlying mechanism of peptide-stimulated ATPase activity of TAP. Maximal NBD closure is induced by the combination of peptide and non-hydrolysable ATP analogs. Thus, TAP1-TAP2 NBD dimers are not fully stabilized by nucleotides alone, and substrate binding plays a key role in inducing the transition state conformations of the NBD. Taken together, these findings show that at least three steps are involved in the transport of peptides across the endoplasmic reticulum membrane for antigen presentation, corresponding to three dynamically and structurally distinct conformational states of TAP. Our studies elucidate structural changes in the TAP NBD in response to nucleotides and substrate, providing new insights into the mechanism of ATP-binding cassette transporter function.
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Affiliation(s)
- Jie Geng
- From the Department of Microbiology and Immunology and
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66
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Ortiz D, Gossack L, Quast U, Bryan J. Reinterpreting the action of ATP analogs on K(ATP) channels. J Biol Chem 2013; 288:18894-902. [PMID: 23665564 DOI: 10.1074/jbc.m113.476887] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Neuroendocrine-type K(ATP) channels, (SUR1/Kir6.2)4, couple the transmembrane flux of K(+), and thus membrane potential, with cellular metabolism in various cell types including insulin-secreting β-cells. Mutant channels with reduced activity are a cause of congenital hyperinsulinism, whereas hyperactive channels are a cause of neonatal diabetes. A current regulatory model proposes that ATP hydrolysis is required to switch SUR1 into post-hydrolytic conformations able to antagonize the inhibitory action of nucleotide binding at the Kir6.2 pore, thus coupling enzymatic and channel activities. Alterations in SUR1 ATPase activity are proposed to contribute to neonatal diabetes and type 2 diabetes risk. The regulatory model is partly based on the reduced ability of ATP analogs such as adenosine 5'-(β,γ-imino)triphosphate (AMP-PNP) and adenosine 5'-O-(thiotriphosphate) (ATPγS) to stimulate channel activity, presumably by reducing hydrolysis. This study uses a substitution at the catalytic glutamate, SUR(1E1507Q), with a significantly increased affinity for ATP, to probe the action of these ATP analogs on conformational switching. ATPγS, a slowly hydrolyzable analog, switches SUR1 conformations, albeit with reduced affinity. Nonhydrolyzable AMP-PNP and adenosine 5'-(β,γ-methylenetriphosphate) (AMP-PCP) alone fail to switch SUR1, but do reverse ATP-induced switching. AMP-PCP displaces 8-azido-[(32)P]ATP from the noncanonical NBD1 of SUR1. This is consistent with structural data on an asymmetric bacterial ABC protein that shows that AMP-PNP binds selectively to the noncanonical NBD to prevent conformational switching. The results imply that MgAMP-PNP and MgAMP-PCP (AMP-PxP) fail to activate K(ATP) channels because they do not support NBD dimerization and conformational switching, rather than by limiting enzymatic activity.
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Affiliation(s)
- David Ortiz
- Pacific Northwest Diabetes Research Institute, Seattle, Washington 98122, USA
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67
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Wen PC, Verhalen B, Wilkens S, Mchaourab HS, Tajkhorshid E. On the origin of large flexibility of P-glycoprotein in the inward-facing state. J Biol Chem 2013; 288:19211-20. [PMID: 23658020 PMCID: PMC3696692 DOI: 10.1074/jbc.m113.450114] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
P-glycoprotein (Pgp) is one of the most biomedically relevant transporters in the ATP binding
cassette (ABC) superfamily due to its involvement in developing multidrug resistance in cancer
cells. Employing molecular dynamics simulations and double electron-electron resonance spectroscopy,
we have investigated the structural dynamics of membrane-bound Pgp in the inward-facing state and
found that Pgp adopts an unexpectedly wide range of conformations, highlighted by the degree of
separation between the two nucleotide-binding domains (NBDs). The distance between the two NBDs in
the equilibrium simulations covers a range of at least 20 Å, including, both, more open and
more closed NBD configurations than the crystal structure. The double electron-electron resonance
measurements on spin-labeled Pgp mutants also show wide distributions covering both longer and
shorter distances than those observed in the crystal structure. Based on structural and sequence
analyses, we propose that the transmembrane domains of Pgp might be more flexible than other
structurally known ABC exporters. The structural flexibility of Pgp demonstrated here is not only in
close agreement with, but also helps rationalize, the reported high NBD fluctuations in several ABC
exporters and possibly represents a fundamental difference in the transport mechanism between ABC
exporters and ABC importers. In addition, during the simulations we have captured partial entrance
of a lipid molecule from the bilayer into the lumen of Pgp, reaching the putative drug binding site.
The location of the protruding lipid suggests a putative pathway for direct drug recruitment from
the membrane.
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Affiliation(s)
- Po-Chao Wen
- Center for Biophysics and Computational Biology, Department of Biochemistry, College of Medicine, and The Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illnois 61801, USA
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68
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Pajeva IK, Hanl M, Wiese M. Protein contacts and ligand binding in the inward-facing model of human P-glycoprotein. ChemMedChem 2013; 8:748-62. [PMID: 23564544 DOI: 10.1002/cmdc.201200491] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2012] [Revised: 02/26/2013] [Indexed: 01/24/2023]
Abstract
The primary aim of this work was to analyze the contacts between residues in the nucleotide binding domains (NBDs) and at the interface between the transmembrane domains (TMDs) and the NBDs in the inward-open homology model of human P-glycoprotein (P-gp). The analysis revealed communication nets through hydrogen bonding in the NBD and at the NBD-TMD interface of each half involving residues from the adenosine triphosphate (ATP) motifs and the coupling helices of the intracellular loops. Similar networks have been identified in P-gp conformations generated by molecular dynamics simulation. Differences have been recorded in the networking between both halves of P-gp. Many of the residue contacts have also been observed in the X-ray crystal structures of other ATP binding cassette (ABC) transporters, which confirms their validity. Next, possible binding pockets involving residues of importance for the TMD-NBD communication were identified. By studying these pockets, binding sites were suggested for rhodamine 123 (R-site) and prazosin (regulatory site) at the NBD-TMD interface that agreed with the experimental data on their location. Additionally, one more R-site in the protein cavity was proposed, in accordance with the available biochemical data. Together with the previously suggested Hoechst 33342 site (H-site), all sites were interpreted with respect to their effects on the protein ATPase activity, in correspondence with the experimental observations. Several residues involved in key contacts in the P-gp NBDs were proposed for further targeted mutagenesis experiments.
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Affiliation(s)
- Ilza K Pajeva
- Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 105, 1113 Sofia, Bulgaria.
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69
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George AM, Jones PM. An asymmetric post-hydrolysis state of the ABC transporter ATPase dimer. PLoS One 2013; 8:e59854. [PMID: 23573213 PMCID: PMC3616075 DOI: 10.1371/journal.pone.0059854] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Accepted: 02/19/2013] [Indexed: 01/30/2023] Open
Abstract
ABC transporters are a superfamily of enzyme pumps that hydrolyse ATP in exchange for translocation of substrates across cellular membranes. Architecturally, ABC transporters are a dimer of transmembrane domains coupled to a dimer of nucleotide binding domains (NBDs): the NBD dimer contains two ATP-binding sites at the intersubunit interface. A current controversy is whether the protomers of the NBD dimer separate during ATP hydrolysis cycling, or remain in constant contact. In order to investigate the ABC ATPase catalytic mechanism, MD simulations using the recent structure of the ADP+Pi-bound MJ0796 isolated NBD dimer were performed. In three independent simulations of the ADP+Pi/apo state, comprising a total of >0.5 µs, significant opening of the apo (empty) active site was observed; occurring by way of intrasubunit rotations between the core and helical subdomains within both NBD monomers. In contrast, in three equivalent simulations of the ATP/apo state, the NBD dimer remained close to the crystal structure, and no opening of either active site occurred. The results thus showed allosteric coupling between the active sites, mediated by intrasubunit conformational changes. Opening of the apo site is exquisitely tuned to the nature of the ligand, and thus to the stage of the reaction cycle, in the opposite site. In addition to this, in also showing how one active site can open, sufficient to bind nucleotide, while the opposite site remains occluded and bound to the hydrolysis products ADP+Pi, the results are consistent with a Constant Contact Model. Conversely, they show how there may be no requirement for the NBD protomers to separate to complete the catalytic cycle.
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Affiliation(s)
- Anthony M George
- School of Medical & Molecular Biosciences, University of Technology Sydney, Broadway, New South Wales, Australia.
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70
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Jones PM, George AM. Mechanism of the ABC transporter ATPase domains: catalytic models and the biochemical and biophysical record. Crit Rev Biochem Mol Biol 2012; 48:39-50. [PMID: 23131203 DOI: 10.3109/10409238.2012.735644] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
ABC transporters comprise a large, diverse, and ubiquitous superfamily of membrane active transporters. Their core architecture is a dimer of dimers, comprising two transmembrane domains that bind substrate and form the channel, and two ATP-binding cassettes, which bind and hydrolyze ATP to energize the translocase function. The prevailing paradigm for the ABC transport mechanism is the Switch Model, in which the nucleotide binding domains are proposed to dimerise upon binding of two ATP molecules, and thence dissociate upon sequential hydrolysis of the ATP. This idea appears consistent with crystal structures of both isolated subunits and whole transporters, as well as with a significant body of biochemical data. Nonetheless, an alternative Constant Contact Model has been proposed, in which the nucleotide binding domains do not fully dissociate, and ATP hydrolysis occurs alternately at each of the two active sites. Here, we review the biochemical and biophysical data relating to the ABC catalytic mechanism, to show how they may be construed as consistent with a Constant Contact Model, and to assess to what extent they support the Switch Model.
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Affiliation(s)
- Peter M Jones
- School of Medical and Molecular Biosciences, University of Technology Sydney, Broadway, NSW, Australia
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71
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Korkhov VM, Mireku SA, Locher KP. Structure of AMP-PNP-bound vitamin B12 transporter BtuCD-F. Nature 2012; 490:367-72. [PMID: 23000901 DOI: 10.1038/nature11442] [Citation(s) in RCA: 139] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2012] [Accepted: 07/26/2012] [Indexed: 01/16/2023]
Abstract
The ATP-binding cassette (ABC) transporter BtuCD mediates the uptake of vitamin B(12) across the inner membrane of Escherichia coli. Previous structures have shown the conformations of apo states, but the transport mechanism has remained unclear. Here we report the 3.5 Å crystal structure of the transporter-binding protein complex BtuCD-BtuF (BtuCD-F) trapped in an β-γ-imidoadenosine 5'-phosphate (AMP-PNP)-bound intermediate state. Although the ABC domains (BtuD subunits) form the expected closed sandwich dimer, the membrane-spanning BtuC subunits adopt a new conformation, with the central translocation pathway sealed by a previously unrecognized cytoplasmic gate. A fully enclosed cavity is thus formed approximately halfway across the membrane. It is large enough to accommodate a vitamin B(12) molecule, and radioligand trapping showed that liposome-reconstituted BtuCD-F indeed contains bound B(12) in the presence of AMP-PNP. In combination with engineered disulphide crosslinking and functional assays, our data suggest an unexpected peristaltic transport mechanism that is distinct from those observed in other ABC transporters.
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Affiliation(s)
- Vladimir M Korkhov
- Institute of Molecular Biology and Biophysics, ETH Zürich, CH-8093 Zürich, Switzerland
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72
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George AM, Jones PM. Perspectives on the structure-function of ABC transporters: the Switch and Constant Contact models. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2012; 109:95-107. [PMID: 22765920 DOI: 10.1016/j.pbiomolbio.2012.06.003] [Citation(s) in RCA: 97] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Accepted: 06/14/2012] [Indexed: 12/20/2022]
Abstract
ABC transporters constitute one of the largest protein families across the kingdoms of archaea, eubacteria and eukarya. They couple ATP hydrolysis to vectorial translocation of diverse substrates across membranes. The ABC transporter architecture comprises two transmembrane domains and two cytosolic ATP-binding cassettes. During 2002-2012, nine prokaryotic ABC transporter structures and two eukaryotic structures have been solved to medium resolution. Despite a wealth of biochemical, biophysical, and structural data, fundamental questions remain regarding the coupling of ATP hydrolysis to unidirectional substrate translocation, and the mechanistic suite of steps involved. The mechanics of the ATP cassette dimer is defined most popularly by the 'Switch Model', which proposes that hydrolysis in each protomer is sequential, and that as the sites are freed of nucleotide, the protomers lose contact across a large solvent-filled gap of 20-30 Å; as captured in several X-ray solved structures. Our 'Constant Contact' model for the operational mechanics of ATP binding and hydrolysis in the ATP-binding cassettes is derived from the 'alternating sites' model, proposed in 1995, and which requires an intrinsic asymmetry in the ATP sites, but does not require the partner protomers to lose contact. Thus one of the most debated issues regarding the function of ABC transporters is whether the cooperative mechanics of ATP hydrolysis requires the ATP cassettes to separate or remain in constant contact and this dilemma is discussed at length in this review.
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Affiliation(s)
- Anthony M George
- School of Medical and Molecular Biosciences, University of Technology Sydney, P.O. Box 123, Broadway, NSW 2007, Australia.
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73
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Kay C, Woodward KD, Lawler K, Self TJ, Dyall SD, Kerr ID. The ATP-binding cassette proteins of the deep-branching protozoan parasite Trichomonas vaginalis. PLoS Negl Trop Dis 2012; 6:e1693. [PMID: 22724033 PMCID: PMC3378599 DOI: 10.1371/journal.pntd.0001693] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2011] [Accepted: 03/18/2012] [Indexed: 02/06/2023] Open
Abstract
The ATP binding cassette (ABC) proteins are a family of membrane transporters and regulatory proteins responsible for diverse and critical cellular process in all organisms. To date, there has been no attempt to investigate this class of proteins in the infectious parasite Trichomonas vaginalis. We have utilized a combination of bioinformatics, gene sequence analysis, gene expression and confocal microscopy to investigate the ABC proteins of T. vaginalis. We demonstrate that, uniquely among eukaryotes, T. vaginalis possesses no intact full-length ABC transporters and has undergone a dramatic expansion of some ABC protein sub-families. Furthermore, we provide preliminary evidence that T. vaginalis is able to read through in-frame stop codons to express ABC transporter components from gene pairs in a head-to-tail orientation. Finally, with confocal microscopy we demonstrate the expression and endoplasmic reticulum localization of a number of T. vaginalis ABC transporters. The parasite Trichomonas vaginalis infects in excess of 100 million people per year, and is a contributory factor to enhanced transmission rates of HIV, the causative virus in AIDS. As such, T. vaginalis infection is an important public health concern. Understanding the biology of the organism is important to determine aspects of the response to drug treatment, host:parasite interactions and so on. We have investigated an important family of proteins – the ATP binding cassette transporters – which are present in the membranes of all cells, and which contribute to a diverse spectrum of important cellular processes. The ABC transporters of T. vaginalis were identified by analysis of primary amino acid sequence data, and examined by subsequent protein and gene expression studies. Our most important conclusion is that – uniquely amongst eukaryotes - T. vaginalis has no ABC transporters capable of acting as monomers. In other words, its ABC transporters must all act by forming functional complexes with other ABC proteins. This has implications for our understanding not just of the parasite's biology, but also its evolution. In summary our analysis opens up the path for future research of individual members of the ABC protein family in T. vaginalis.
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Affiliation(s)
- Christopher Kay
- School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, United Kingdom
| | - Katharine D. Woodward
- School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, United Kingdom
| | - Karen Lawler
- School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, United Kingdom
| | - Tim J. Self
- School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, United Kingdom
| | - Sabrina D. Dyall
- School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, United Kingdom
- Department of Biosciences, University of Mauritius, Reduit, Mauritius
| | - Ian D. Kerr
- School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, United Kingdom
- * E-mail:
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74
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Corradi V, Singh G, Tieleman DP. The human transporter associated with antigen processing: molecular models to describe peptide binding competent states. J Biol Chem 2012; 287:28099-111. [PMID: 22700967 PMCID: PMC3431710 DOI: 10.1074/jbc.m112.381251] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human transporter associated with antigen processing (TAP) is a member of the ATP binding cassette (ABC) transporter superfamily. TAP plays an essential role in the antigen presentation pathway by translocating cytosolic peptides derived from proteasomal degradation into the endoplasmic reticulum lumen. Here, the peptides are loaded into major histocompatibility class I molecules to be in turn exposed at the cell surface for recognition by T-cells. TAP is a heterodimer formed by the association of two half-transporters, TAP1 and TAP2, with a typical ABC transporter core that consists of two nucleotide binding domains and two transmembrane domains. Despite the availability of biological data, a full understanding of the mechanism of action of TAP is limited by the absence of experimental structures of the full-length transporter. Here, we present homology models of TAP built on the crystal structures of P-glycoprotein, ABCB10, and Sav1866. The models represent the transporter in inward- and outward-facing conformations that could represent initial and final states of the transport cycle, respectively. We described conserved regions in the endoplasmic reticulum-facing loops with a role in the opening and closing of the cavity. We also identified conserved π-stacking interactions in the cytosolic part of the transmembrane domains that could explain the experimental data available for TAP1-Phe-265. Electrostatic potential calculations gave structural insights into the role of residues involved in peptide binding, such as TAP1-Val-288, TAP2-Cys-213, TAP2-Met-218. Moreover, these calculations identified additional residues potentially involved in peptide binding, in turn verified with replica exchange simulations performed on a peptide bound to the inward-facing models.
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Affiliation(s)
- Valentina Corradi
- Department of Biological Sciences and Institute for Biocomplexity and Informatics, University of Calgary, Calgary, Alberta T2N 1N4, Canada
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75
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Meena SR, Gangwar SP, Saxena AK. Purification, crystallization and preliminary X-ray crystallographic analysis of the ATPase domain of human TAP in nucleotide-free and ADP-, vanadate- and azide-complexed forms. Acta Crystallogr Sect F Struct Biol Cryst Commun 2012; 68:655-8. [PMID: 22684063 PMCID: PMC3370903 DOI: 10.1107/s1744309112013954] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Accepted: 03/30/2012] [Indexed: 11/10/2022]
Abstract
The human transporter associated with antigen processing (TAP) protein belongs to the ATP-binding cassette (ABC) transporter superfamily and is formed by the heterodimerization of TAP1 and TAP2 subunits. TAP selectively pumps cytosolic peptides into the lumen of the endoplasmic reticulum in an ATP-dependent manner. The catalytic cycle of the ATPase domain of TAP is not understood at the molecular level. The structures of catalytic intermediates of the ATPase domain of TAP will contribute to the understanding of the chemical mechanism of ATP hydrolysis. In order to understand this mechanism, the ATPase domain of human TAP1 (NBD1) was expressed and purified, crystallized in nucleotide-free and transition-state complex forms and X-ray crystallographic studies were performed. The NBD1 protein was crystallized (i) in the nucleotide-free apo form; (ii) in complex with ADP-Mg(2+), mimicking the product-bound state; (iii) in complex with vanadate-ADP-Mg(2+), mimicking the ATP-bound state; and (iv) in complex with azide-ADP-Mg(2+), also mimicking the ATP-bound state. X-ray diffraction data sets were collected for apo and complexed NBD1 using an in-house X-ray diffraction facility at a wavelength of 1.5418 Å. The apo and complexed NBD1 crystals belonged to the primitive hexagonal space group P6(2), with one monomer in the asymmetric unit. Here, the crystallization, data collection and preliminary crystallographic analysis of apo and complexed NBD1 are reported.
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Affiliation(s)
- Sita R. Meena
- Structural Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, USA
| | - Shanti P. Gangwar
- Structural Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, USA
| | - Ajay K. Saxena
- Structural Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, USA
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76
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Ortiz D, Voyvodic P, Gossack L, Quast U, Bryan J. Two neonatal diabetes mutations on transmembrane helix 15 of SUR1 increase affinity for ATP and ADP at nucleotide binding domain 2. J Biol Chem 2012; 287:17985-95. [PMID: 22451668 DOI: 10.1074/jbc.m112.349019] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
K(ATP) channels, (SUR1/Kir6.2)(4) (sulfonylurea receptor type 1/potassium inward rectifier type 6.2) respond to the metabolic state of pancreatic β-cells, modulating membrane potential and insulin exocytosis. Mutations in both subunits cause neonatal diabetes by overactivating the pore. Hyperactive channels fail to close appropriately with increased glucose metabolism; thus, β-cell hyperpolarization limits insulin release. K(ATP) channels are inhibited by ATP binding to the Kir6.2 pore and stimulated, via an uncertain mechanism, by magnesium nucleotides at SUR1. Glibenclamide (GBC), a sulfonylurea, was used as a conformational probe to compare nucleotide action on wild type versus Q1178R and R1182Q SUR1 mutants. GBC binds with high affinity to aporeceptors, presumably in the inward facing ATP-binding cassette configuration; MgATP reduces binding affinity via a shift to the outward facing conformation. To determine nucleotide affinities under equilibrium, non-hydrolytic conditions, Mg(2+) was eliminated. A four-state equilibrium model describes the allosteric linkage. The K(D) for ATP(4-) is ~1 versus 12 mM, Q1178R versus wild type, respectively. The linkage constant is ~10, implying that outward facing conformations bind GBC with a lower affinity, 9-10 nM for Q1178R. Thus, nucleotides cannot completely inhibit GBC binding. Binding of channel openers is reported to require ATP hydrolysis, but diazoxide, a SUR1-selective agonist, concentration-dependently augments ATP(4-) action. An eight-state model describes linkage between diazoxide and ATP(4-) binding; diazoxide markedly increases the affinity of Q1178R for ATP(4-) and ATP(4-) augments diazoxide binding. NBD2, but not NBD1, has a higher affinity for ATP (and ADP) in mutant versus wild type (with or without Mg(2+)). Thus, the mutants spend more time in nucleotide-bound conformations, with reduced affinity for GBC, that activate the pore.
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Affiliation(s)
- David Ortiz
- Graduate Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA
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77
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Crystal structure of a heterodimeric ABC transporter in its inward-facing conformation. Nat Struct Mol Biol 2012; 19:395-402. [PMID: 22447242 DOI: 10.1038/nsmb.2267] [Citation(s) in RCA: 195] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Accepted: 02/17/2012] [Indexed: 11/08/2022]
Abstract
ATP-binding cassette (ABC) transporters shuttle a wide variety of molecules across cell membranes by alternating between inward- and outward-facing conformations, harnessing the energy of ATP binding and hydrolysis at their nucleotide binding domains (NBDs). Here we present the 2.9-Å crystal structure of the heterodimeric ABC transporter TM287-TM288 (TM287/288) from Thermotoga maritima in its inward-facing state. In contrast to previous studies, we found that the NBDs only partially separate, remaining in contact through an interface involving conserved motifs that connect the two ATP hydrolysis sites. We observed AMP-PNP binding to the degenerate catalytic site, which deviates from the consensus sequence in the same positions as the eukaryotic homologs CFTR and TAP1-TAP2 (TAP1/2). The TM287/288 structure provides unprecedented insights into the mechanism of heterodimeric ABC exporters and will enable future studies on this large transporter superfamily.
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78
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Jones PM, George AM. Role of the D-loops in allosteric control of ATP hydrolysis in an ABC transporter. J Phys Chem A 2012; 116:3004-13. [PMID: 22369471 DOI: 10.1021/jp211139s] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
ABC transporters couple ATP hydrolysis to movement of substrates across cell membranes. They comprise two transmembrane domains and two cytosolic nucleotide-binding domains forming two active sites that hydrolyze ATP cooperatively. The mechanism of ATP hydrolysis is controversial and the structural dynamic basis of its allosteric control unknown. Here we report molecular dynamics simulations of the ATP/apo and ATP/ADP states of the bacterial ABC exporter Sav1866, in which the cytoplasmic region of the protein was simulated in explicit water for 150 ns. In the simulation of the ATP/apo state, we observed, for the first time, conformers of the active site with the canonical geometry for an in-line nucleophilic attack on the ATP γ-phosphate. The conserved glutamate immediately downstream of the Walker B motif is the catalytic base, forming a dyad with the H-loop histidine, whereas the Q-loop glutamine has an organizing role. Each D-loop provides a coordinating residue of the attacking water, and comparison with the simulation of the ATP/ADP state suggests that via their flexibility, the D-loops modulate formation of the hydrolysis-competent state. A global switch involving a coupling helix delineates the signal transmission route by which allosteric control of ATP hydrolysis in ABC transporters is mediated.
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Affiliation(s)
- Peter M Jones
- School of Medical and Molecular Biosciences, and iThree Institute, University of Technology Sydney, P.O. Box 123, Broadway, NSW 2007, Australia.
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79
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The TAP translocation machinery in adaptive immunity and viral escape mechanisms. Essays Biochem 2012; 50:249-64. [PMID: 21967061 DOI: 10.1042/bse0500249] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The adaptive immune system plays an essential role in protecting vertebrates against a broad range of pathogens and cancer. The MHC class I-dependent pathway of antigen presentation represents a sophisticated cellular machinery to recognize and eliminate infected or malignantly transformed cells, taking advantage of the proteasomal turnover of the cell's proteome. TAP (transporter associated with antigen processing) 1/2 (ABCB2/3, where ABC is ATP-binding cassette) is the principal component in the recognition, translocation, chaperoning, editing and final loading of antigenic peptides on to MHC I complexes in the ER (endoplasmic reticulum) lumen. These different tasks are co-ordinated within a dynamic macromolecular peptide-loading complex consisting of TAP1/2 and various auxiliary factors, such as the adapter protein tapasin, the oxidoreductase ERp57, the lectin chaperone calreticulin, and the final peptide acceptor the MHC I heavy chain associated with β2-microglobulin. In this chapter, we summarize the structural organization and molecular mechanism of the antigen-translocation machinery as well as various modes of regulation by viral factors and in genetic diseases and tumour development.
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80
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Abstract
ABC (ATP-binding cassette) transporters are arguably the most important family of ATP-driven transporters in biology. Despite considerable effort and advances in determining the structures and physiology of these transporters, their fundamental molecular mechanisms remain elusive and highly controversial. How does ATP hydrolysis by ABC transporters drive their transport function? Part of the problem in answering this question appears to be a perceived need to formulate a universal mechanism. Although it has been generally hoped and assumed that the whole superfamily of ABC transporters would exhibit similar conserved mechanisms, this is proving not to be the case. Structural considerations alone suggest that there are three overall types of coupling mechanisms related to ABC exporters, small ABC importers and large ABC importers. Biochemical and biophysical characterization leads us to the conclusion that, even within these three classes, the catalytic and transport mechanisms are not fully conserved, but continue to evolve. ABC transporters also exhibit unusual characteristics not observed in other primary transporters, such as uncoupled basal ATPase activity, that severely complicate mechanistic studies by established methods. In this chapter, I review these issues as related to ABC exporters in particular. A consensus view has emerged that ABC exporters follow alternating-access switch transport mechanisms. However, some biochemical data suggest that alternating catalytic site transport mechanisms are more appropriate for fully symmetrical ABC exporters. Heterodimeric and asymmetrical ABC exporters appear to conform to simple alternating-access-type mechanisms.
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81
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Pinto RD, Pereira PJB, dos Santos NMS. Transporters associated with antigen processing (TAP) in sea bass (Dicentrarchus labrax, L.): molecular cloning and characterization of TAP1 and TAP2. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2011; 35:1173-1181. [PMID: 21540052 DOI: 10.1016/j.dci.2011.03.024] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Revised: 03/15/2011] [Accepted: 03/17/2011] [Indexed: 05/30/2023]
Abstract
The transporters associated with antigen processing (TAP), play an important role in the MHC class I antigen presentation pathway. In this work, sea bass (Dicentrarchus labrax) TAP1 and TAP2 genes and transcripts were isolated and characterized. Only the TAP2 gene is structurally similar to its human orthologue. As other TAP molecules, sea bass TAP1 and TAP2 are formed by one N-terminal accessory domain, one core membrane-spanning domain and one canonical C-terminal nucleotide-binding domain. Homology modelling of the sea bass TAP dimer predicts that its quaternary structure is in accordance with that of other ABC transporters. Phylogenetic analysis segregates sea bass TAP1 and TAP2 into each subfamily cluster of transporters, placing them in the fish class and suggesting that the basic structure of these transport-associated proteins is evolutionarily conserved. Furthermore, the present data provides information that will enable more studies on the class I antigen presentation pathway in this important fish species.
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Affiliation(s)
- Rute D Pinto
- Fish Immunology and Vaccinology Group, IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
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82
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83
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Abstract
ATP-binding cassette transporters are powered by ATP, but the mechanism by which these transporters hydrolyze ATP is unclear. In this study, four crystal structures of the full-length wild-type maltose transporter, stabilized by adenosine 5'-(β,γ-imido)triphosphate or ADP in conjunction with phosphate analogs BeF(3)(-), VO(4)(3-), or AIF(4)(-), were determined to 2.2- to 2.4-Å resolution. These structures led to the assignment of two enzymatic states during ATP hydrolysis and demonstrate specific functional roles of highly conserved residues in the nucleotide-binding domain, suggesting that ATP-binding cassette transporters catalyze ATP hydrolysis via a general base mechanism.
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84
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Yang R, Hou YX, Campbell CA, Palaniyandi K, Zhao Q, Bordner AJ, Chang XB. Glutamine residues in Q-loops of multidrug resistance protein MRP1 contribute to ATP binding via interaction with metal cofactor. BIOCHIMICA ET BIOPHYSICA ACTA 2011; 1808:1790-6. [PMID: 21315686 PMCID: PMC3091947 DOI: 10.1016/j.bbamem.2011.02.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 12/10/2010] [Revised: 01/07/2011] [Accepted: 02/03/2011] [Indexed: 10/18/2022]
Abstract
Structural analyses of bacterial ATP-binding-cassette transporters revealed that the glutamine residue in Q-loop plays roles in interacting with: 1) a metal cofactor to participate in ATP binding; 2) a putative catalytic water molecule to participate in ATP hydrolysis; 3) other residues to transmit the conformational changes between nucleotide-binding-domains and transmembrane-domains, in ATP-dependent solute transport. We have mutated the glutamines at 713 and 1375 to asparagine, methionine or leucine to determine the functional roles of these residues in Q-loops of MRP1. All these single mutants significantly decreased Mg·ATP binding and increased the K(m) (Mg·ATP) and V(max) values in Mg·ATP-dependent leukotriene-C4 transport. However, the V(max) values of the double mutants Q713N/Q1375N, Q713M/Q1375M and Q713L/Q1375L were lower than that of wtMRP1, implying that the double mutants cannot efficiently bind Mg·ATP. Interestingly, MRP1 has higher affinity for Mn·ATP than for Mg·ATP and the Mn·ATP-dependent leukotriene-C4 transport activities of Q713N/Q1375N and Q713M/Q1375M are significantly higher than that of wtMRP1. All these results suggest that: 1) the glutamine residues in Q-loops contribute to ATP-binding via interaction with a metal cofactor; 2) it is most unlikely that these glutamine residues would play crucial roles in ATP hydrolysis and in transmitting the conformational changes between nucleotide-binding-domains and transmembrane-domains.
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Affiliation(s)
- Runying Yang
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Mayo Clinic Arizona, Scottsdale, AZ 85259, USA
| | - Yue-xian Hou
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Mayo Clinic Arizona, Scottsdale, AZ 85259, USA
| | - Chase A. Campbell
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Mayo Clinic Arizona, Scottsdale, AZ 85259, USA
| | - Kanagaraj Palaniyandi
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Mayo Clinic Arizona, Scottsdale, AZ 85259, USA
| | - Qing Zhao
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Mayo Clinic Arizona, Scottsdale, AZ 85259, USA
| | - Andrew J. Bordner
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Mayo Clinic Arizona, Scottsdale, AZ 85259, USA
| | - Xiu-bao Chang
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Mayo Clinic Arizona, Scottsdale, AZ 85259, USA
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85
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Schaefer A, Miertzschke M, Berken A, Wittinghofer A. Dimeric plant RhoGAPs are regulated by its CRIB effector motif to stimulate a sequential GTP hydrolysis. J Mol Biol 2011; 411:808-22. [PMID: 21723292 DOI: 10.1016/j.jmb.2011.06.033] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 06/16/2011] [Accepted: 06/16/2011] [Indexed: 11/25/2022]
Abstract
RopGAPs are GTPase-activating proteins (GAPs) for plant Rho proteins (ROPs). The largest RopGAP family is characterized by the plant-specific combination of a classical RhoGAP domain and a Cdc42/Rac interactive binding (CRIB) motif, which, in animal and fungi, has never been found in GAPs but in effectors for Cdc42 and Rac1. Very little is known about the molecular mechanism of the RopGAP activity including the regulatory role of the CRIB motif. Previously, we have shown that they are dimeric and form a 2:2 complex with ROPs. Here, we analyze the kinetics of the GAP-mediated GTP hydrolysis of ROPs using wild-type and mutant RopGAP2 from Arabidopsis thaliana. For an efficient GAP activity, RopGAP2 requires both the catalytic Arg159 in its GAP domain indicating a similar catalytic machinery as in animal RhoGAPs and the CRIB motif, which mediates high affinity and specificity in binding. The dimeric RopGAP2 is unique in that it stimulates ROP·GTP hydrolysis in a sequential manner with a 10-fold difference between the hydrolysis rates of the two active sites. Using particular CRIB point and deletion mutants lead us to conclude that the sequential mechanism is likely due to steric hindrance induced by the Arg fingers and/or the CRIB motifs after binding of two ROP molecules.
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Affiliation(s)
- Antje Schaefer
- Department of Structural Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn Str. 11, 44227 Dortmund, Germany
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86
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Szollosi A, Muallem DR, Csanády L, Vergani P. Mutant cycles at CFTR's non-canonical ATP-binding site support little interface separation during gating. J Gen Physiol 2011; 137:549-62. [PMID: 21576373 PMCID: PMC3105517 DOI: 10.1085/jgp.201110608] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Accepted: 04/20/2011] [Indexed: 01/27/2023] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel belonging to the adenosine triphosphate (ATP)-binding cassette (ABC) superfamily. ABC proteins share a common molecular mechanism that couples ATP binding and hydrolysis at two nucleotide-binding domains (NBDs) to diverse functions. This involves formation of NBD dimers, with ATP bound at two composite interfacial sites. In CFTR, intramolecular NBD dimerization is coupled to channel opening. Channel closing is triggered by hydrolysis of the ATP molecule bound at composite site 2. Site 1, which is non-canonical, binds nucleotide tightly but is not hydrolytic. Recently, based on kinetic arguments, it was suggested that this site remains closed for several gating cycles. To investigate movements at site 1 by an independent technique, we studied changes in thermodynamic coupling between pairs of residues on opposite sides of this site. The chosen targets are likely to interact based on both phylogenetic analysis and closeness on structural models. First, we mutated T460 in NBD1 and L1353 in NBD2 (the corresponding site-2 residues become energetically coupled as channels open). Mutation T460S accelerated closure in hydrolytic conditions and in the nonhydrolytic K1250R background; mutation L1353M did not affect these rates. Analysis of the double mutant showed additive effects of mutations, suggesting that energetic coupling between the two residues remains unchanged during the gating cycle. We next investigated pairs 460-1348 and 460-1375. Although both mutations H1348A and H1375A produced dramatic changes in hydrolytic and nonhydrolytic channel closing rates, in the corresponding double mutants these changes proved mostly additive with those caused by mutation T460S, suggesting little change in energetic coupling between either positions 460-1348 or positions 460-1375 during gating. These results provide independent support for a gating model in which ATP-bound composite site 1 remains closed throughout the gating cycle.
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Affiliation(s)
- Andras Szollosi
- Department of Medical Biochemistry, Semmelweis University, Budapest H-1094, Hungary
| | - Daniella R. Muallem
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, England, UK
| | - László Csanády
- Department of Medical Biochemistry, Semmelweis University, Budapest H-1094, Hungary
| | - Paola Vergani
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, England, UK
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87
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Ohnuma S, Chufan E, Nandigama K, Miller Jenkins LM, Durell SR, Appella E, Sauna ZE, Ambudkar SV. Inhibition of multidrug resistance-linked P-glycoprotein (ABCB1) function by 5'-fluorosulfonylbenzoyl 5'-adenosine: evidence for an ATP analogue that interacts with both drug-substrate-and nucleotide-binding sites. Biochemistry 2011; 50:3724-35. [PMID: 21452853 PMCID: PMC3108491 DOI: 10.1021/bi200073f] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
5'-Fluorosulfonylbenzonyl 5'-adenosine (FSBA) is an ATP analogue that covalently modifies several residues in the nucleotide-binding domains (NBDs) of several ATPases, kinases, and other proteins. P-glycoprotein (P-gp, ABCB1) is a member of the ATP-binding cassette (ABC) transporter superfamily that utilizes energy from ATP hydrolysis for the efflux of amphipathic anticancer agents from cancer cells. We investigated the interactions of FSBA with P-gp to study the catalytic cycle of ATP hydrolysis. Incubation of P-gp with FSBA inhibited ATP hydrolysis (IC(50 )= 0.21 mM) and the binding of 8-azido[α-(32)P]ATP (IC(50) = 0.68 mM). In addition, (14)C-FSBA cross-links to P-gp, suggesting that FSBA-mediated inhibition of ATP hydrolysis is irreversible due to covalent modification of P-gp. However, when the NBDs were occupied with a saturating concentration of ATP prior to treatment, FSBA stimulated ATP hydrolysis by P-gp. Furthermore, FSBA inhibited the photo-cross-linking of P-gp with [(125)I]iodoarylazidoprazosin (IAAP; IC(50) = 0.17 mM). As IAAP is a transport substrate for P-gp, this suggests that FSBA affects not only the NBDs but also the transport-substrate site in the transmembrane domains. Consistent with these results, FSBA blocked efflux of rhodamine 123 from P-gp-expressing cells. Additionally, mass spectrometric analysis identified FSBA cross-links to residues within or nearby the NBDs but not in the transmembrane domains, and docking of FSBA in a homology model of human P-gp NBDs supports the biochemical studies. Thus, FSBA is an ATP analogue that interacts with both the drug-binding and ATP-binding sites of P-gp, but fluorosulfonyl-mediated cross-linking is observed only at the NBDs.
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Affiliation(s)
- Shinobu Ohnuma
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4256
| | - Eduardo Chufan
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4256
| | - Krishnamachary Nandigama
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4256
| | - Lisa M. Miller Jenkins
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4256
| | - Stewart R. Durell
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4256
| | - Ettore Appella
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4256
| | - Zuben E. Sauna
- Laboratory of Hemostasis, Division of Hematology, Center for Biologics Evaluation and Research, US Food and Drug Administration, Bethesda, Maryland 20892
| | - Suresh V. Ambudkar
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4256
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88
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Prasad R, Sharma M, Rawal MK. Functionally Relevant Residues of Cdr1p: A Multidrug ABC Transporter of Human Pathogenic Candida albicans. JOURNAL OF AMINO ACIDS 2011; 2011:531412. [PMID: 22312462 PMCID: PMC3268037 DOI: 10.4061/2011/531412] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/24/2010] [Accepted: 02/21/2011] [Indexed: 12/18/2022]
Abstract
Reduced intracellular accumulation of drugs (due to rapid efflux) mediated by the efflux pump proteins belonging to ABC (ATP Binding Cassette) and MFS (Major Facilitators) superfamily is one of the most common strategies adopted by multidrug resistance (MDR) pathogenic yeasts. To combat MDR, it is essential to understand the structure and function of these transporters so that inhibitors/modulators to these can be developed. The sequence alignments of the ABC transporters reveal selective divergence within much conserved domains of Nucleotide-Binding Domains (NBDs) which is unique to all fungal transporters. Recently, the role of conserved but divergent residues of Candida Drug Resistance 1 (CDR1), an ABC drug transporter of human pathogenic Candida albicans, has been examined with regard to ATP binding and hydrolysis. In this paper, we focus on some of the recent advances on the relevance of divergent and conserved amino acids of CaCdr1p and also discuss as to how drug interacts with Trans Membrane Domains (TMDs) residues for its extrusion from MDR cells.
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Affiliation(s)
- Rajendra Prasad
- Membrane Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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89
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Schölz C, Parcej D, Ejsing CS, Robenek H, Urbatsch IL, Tampé R. Specific lipids modulate the transporter associated with antigen processing (TAP). J Biol Chem 2011; 286:13346-56. [PMID: 21357424 DOI: 10.1074/jbc.m110.216416] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The transporter associated with antigen processing (TAP) plays a key role in adaptive immunity by translocating proteasomal degradation products from the cytosol into the endoplasmic reticulum lumen for subsequent loading onto major histocompatibility (MHC) class I molecules. For functional and structural analysis of this ATP-binding cassette complex, we established the overexpression of TAP in the methylotrophic yeast Pichia pastoris. Screening of optimal solubilization and purification conditions allowed the isolation of the heterodimeric transport complex, yielding 30 mg of TAP/liter of culture. Detailed analysis of TAP function in the membrane, solubilized, purified, and reconstituted states revealed a direct influence of the native lipid environment on activity. TAP-associated phospholipids, essential for function, were profiled by liquid chromatography Fourier transform mass spectrometry. The antigen translocation activity is stimulated by phosphatidylinositol and -ethanolamine, whereas cholesterol has a negative effect on TAP activity.
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Affiliation(s)
- Christian Schölz
- Institute of Biochemistry, Biocenter, Goethe-University Frankfurt, Max-von-Laue Strasse 9, D-60438 Frankfurt am Main, Germany
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90
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Kelly L, Fukushima H, Karchin R, Gow JM, Chinn LW, Pieper U, Segal MR, Kroetz DL, Sali A. Functional hot spots in human ATP-binding cassette transporter nucleotide binding domains. Protein Sci 2011; 19:2110-21. [PMID: 20799350 DOI: 10.1002/pro.491] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The human ATP-binding cassette (ABC) transporter superfamily consists of 48 integral membrane proteins that couple the action of ATP binding and hydrolysis to the transport of diverse substrates across cellular membranes. Defects in 18 transporters have been implicated in human disease. In hundreds of cases, disease phenotypes and defects in function can be traced to nonsynonymous single nucleotide polymorphisms (nsSNPs). The functional impact of the majority of ABC transporter nsSNPs has yet to be experimentally characterized. Here, we combine experimental mutational studies with sequence and structural analysis to describe the impact of nsSNPs in human ABC transporters. First, the disease associations of 39 nsSNPs in 10 transporters were rationalized by identifying two conserved loops and a small α-helical region that may be involved in interdomain communication necessary for transport of substrates. Second, an approach to discriminate between disease-associated and neutral nsSNPs was developed and tailored to this superfamily. Finally, the functional impact of 40 unannotated nsSNPs in seven ABC transporters identified in 247 ethnically diverse individuals studied by the Pharmacogenetics of Membrane Transporters consortium was predicted. Three predictions were experimentally tested using human embryonic kidney epithelial (HEK) 293 cells stably transfected with the reference multidrug resistance transporter 4 and its variants to examine functional differences in transport of the antiviral drug, tenofovir. The experimental results confirmed two predictions. Our analysis provides a structural and evolutionary framework for rationalizing and predicting the functional effects of nsSNPs in this clinically important membrane transporter superfamily.
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Affiliation(s)
- Libusha Kelly
- Graduate Group in Bioinformatics, University of California at San Francisco, San Francisco, California, USA
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91
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Zutz A, Hoffmann J, Hellmich UA, Glaubitz C, Ludwig B, Brutschy B, Tampé R. Asymmetric ATP hydrolysis cycle of the heterodimeric multidrug ABC transport complex TmrAB from Thermus thermophilus. J Biol Chem 2010; 286:7104-15. [PMID: 21190941 DOI: 10.1074/jbc.m110.201178] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
ATP-binding cassette (ABC) systems translocate a wide range of solutes across cellular membranes. The thermophilic gram-negative eubacterium Thermus thermophilus, a model organism for structural genomics and systems biology, discloses ∼46 ABC proteins, which are largely uncharacterized. Here, we functionally analyzed the first two and only ABC half-transporters of the hyperthermophilic bacterium, TmrA and TmrB. The ABC system mediates uptake of the drug Hoechst 33342 in inside-out oriented vesicles that is inhibited by verapamil. TmrA and TmrB form a stable heterodimeric complex hydrolyzing ATP with a K(m) of 0.9 mm and k(cat) of 9 s(-1) at 68 °C. Two nucleotides can be trapped in the heterodimeric ABC complex either by vanadate or by mutation inhibiting ATP hydrolysis. Nucleotide trapping requires permissive temperatures, at which a conformational ATP switch is possible. We further demonstrate that the canonic glutamate 523 of TmrA is essential for rapid conversion of the ATP/ATP-bound complex into its ADP/ATP state, whereas the corresponding aspartate in TmrB (Asp-500) has only a regulatory role. Notably, exchange of this single noncanonic residue into a catalytic glutamate cannot rescue the function of the E523Q/D500E complex, implicating a built-in asymmetry of the complex. However, slow ATP hydrolysis in the newly generated canonic site (D500E) strictly depends on the formation of a posthydrolysis state in the consensus site, indicating an allosteric coupling of both active sites.
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Affiliation(s)
- Ariane Zutz
- Institute of Biochemistry, Biocenter, Goethe-University Frankfurt, D-60438 Frankfurt, Germany
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92
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Szollosi A, Vergani P, Csanády L. Involvement of F1296 and N1303 of CFTR in induced-fit conformational change in response to ATP binding at NBD2. J Gen Physiol 2010; 136:407-23. [PMID: 20876359 PMCID: PMC2947058 DOI: 10.1085/jgp.201010434] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2010] [Accepted: 09/07/2010] [Indexed: 11/20/2022] Open
Abstract
The chloride ion channel cystic fibrosis transmembrane conductance regulator (CFTR) displays a typical adenosine trisphosphate (ATP)-binding cassette (ABC) protein architecture comprising two transmembrane domains, two intracellular nucleotide-binding domains (NBDs), and a unique intracellular regulatory domain. Once phosphorylated in the regulatory domain, CFTR channels can open and close when supplied with cytosolic ATP. Despite the general agreement that formation of a head-to-tail NBD dimer drives the opening of the chloride ion pore, little is known about how ATP binding to individual NBDs promotes subsequent formation of this stable dimer. Structural studies on isolated NBDs suggest that ATP binding induces an intra-domain conformational change termed "induced fit," which is required for subsequent dimerization. We investigated the allosteric interaction between three residues within NBD2 of CFTR, F1296, N1303, and R1358, because statistical coupling analysis suggests coevolution of these positions, and because in crystal structures of ABC domains, interactions between these positions appear to be modulated by ATP binding. We expressed wild-type as well as F1296S, N1303Q, and R1358A mutant CFTR in Xenopus oocytes and studied these channels using macroscopic inside-out patch recordings. Thermodynamic mutant cycles were built on several kinetic parameters that characterize individual steps in the gating cycle, such as apparent affinities for ATP, open probabilities in the absence of ATP, open probabilities in saturating ATP in a mutant background (K1250R), which precludes ATP hydrolysis, as well as the rates of nonhydrolytic closure. Our results suggest state-dependent changes in coupling between two of the three positions (1296 and 1303) and are consistent with a model that assumes a toggle switch-like interaction pattern during the intra-NBD2 induced fit in response to ATP binding. Stabilizing interactions of F1296 and N1303 present before ATP binding are replaced by a single F1296-N1303 contact in ATP-bound states, with similar interaction partner toggling occurring during the much rarer ATP-independent spontaneous openings.
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Affiliation(s)
- Andras Szollosi
- Department of Medical Biochemistry, Semmelweis University, Budapest H-1094, Hungary
| | - Paola Vergani
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 7HY, England, UK
| | - László Csanády
- Department of Medical Biochemistry, Semmelweis University, Budapest H-1094, Hungary
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93
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Tsai MF, Jih KY, Shimizu H, Li M, Hwang TC. Optimization of the degenerated interfacial ATP binding site improves the function of disease-related mutant cystic fibrosis transmembrane conductance regulator (CFTR) channels. J Biol Chem 2010; 285:37663-71. [PMID: 20861014 DOI: 10.1074/jbc.m110.172817] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel, an ATP binding cassette (ABC) protein whose defects cause the deadly genetic disease cystic fibrosis (CF), encompasses two nucleotide binding domains (NBD1 and NBD2). Recent studies indicate that in the presence of ATP, the two NBDs coalesce into a dimer, trapping an ATP molecule in each of the two interfacial composite ATP binding sites (site 1 and site 2). Experimental evidence also suggests that CFTR gating is mainly controlled by ATP binding and hydrolysis in site 2, whereas site 1, which harbors several non-canonical substitutions in ATP-interacting motifs, is considered degenerated. The CF-associated mutation G551D, by introducing a bulky and negatively charged side chain into site 2, completely abolishes ATP-induced openings of CFTR. Here, we report a strategy to optimize site 1 for ATP binding by converting two amino acid residues to ABC consensus (i.e. H1348G) or more commonly seen residues in other ABC proteins (i.e. W401Y,W401F). Introducing either one or both of these mutations into G551D-CFTR confers ATP responsiveness for this disease-associated mutant channel. We further showed that the same maneuver also improved the function of WT-CFTR and the most common CF-associated ΔF508 channels, both of which rely on site 2 for gating control. Thus, our results demonstrated that the degenerated site 1 can be rebuilt to complement or support site 2 for CFTR function. Possible approaches for developing CFTR potentiators targeting site 1 will be discussed.
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Affiliation(s)
- Ming-Feng Tsai
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri 65211, USA
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94
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Kumar A, Shukla S, Mandal A, Shukla S, Ambudkar SV, Prasad R. Divergent signature motifs of nucleotide binding domains of ABC multidrug transporter, CaCdr1p of pathogenic Candida albicans, are functionally asymmetric and noninterchangeable. BIOCHIMICA ET BIOPHYSICA ACTA 2010; 1798:1757-66. [PMID: 20546701 PMCID: PMC2917344 DOI: 10.1016/j.bbamem.2010.05.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Revised: 05/03/2010] [Accepted: 05/17/2010] [Indexed: 02/04/2023]
Abstract
Nucleotide binding domains (NBDs) of the multidrug transporter of Candida albicans, CaCdr1p, possess unique divergent amino acids in their conserved motifs. For example, NBD1 (N-terminal-NBD) possesses conserved signature motifs, while the same motif is divergent in NBD2 (C-terminal-NBD). In this study, we have evaluated the contribution of these conserved and divergent signature motifs of CaCdr1p in ATP catalysis and drug transport. By employing site-directed mutagenesis, we made three categories of mutant variants. These included mutants where all the signature motif residues were replaced with either alanines or mutants with exchanged equipositional residues to mimic the conservancy and degeneracy in opposite domain. In addition, a set of mutants where signature motifs were swapped to have variants with either both the conserved or degenerated entire signature motif. We observed that conserved and equipositional residues of NBD1 and NBD2 and swapped signature motif mutants showed high susceptibility to all the tested drugs with simultaneous abrogation in ATPase and R6G efflux activities. However, some of the mutants displayed a selective increase in susceptibility to the drugs. Notably, none of the mutant variants and WT-CaCdr1p showed any difference in drug and nucleotide binding. Our mutational analyses show not only that certain conserved residues of NBD1 signature sequence (S304, G306, and E307) are important in ATP hydrolysis and R6G efflux but also that a few divergent residues (N1002 and E1004) of NBD2 signature motif have evolved to be functionally relevant and are not interchangeable. Taken together, our data suggest that the signature motifs of CaCdr1p, whether it is divergent or conserved, are nonexchangeable and are functionally critical for ATP hydrolysis.
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Affiliation(s)
- Antresh Kumar
- Membrane Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Suneet Shukla
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4254, USA
| | - Ajeet Mandal
- Membrane Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Sudhanshu Shukla
- Laboratory of Immune Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4254, USA
| | - Suresh V. Ambudkar
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4254, USA
| | - Rajendra Prasad
- Membrane Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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95
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Haffke M, Menzel A, Carius Y, Jahn D, Heinz DW. Structures of the nucleotide-binding domain of the human ABCB6 transporter and its complexes with nucleotides. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2010; 66:979-87. [PMID: 20823549 DOI: 10.1107/s0907444910028593] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2010] [Accepted: 07/17/2010] [Indexed: 02/01/2023]
Abstract
The human ATP-binding cassette (ABC) transporter ABCB6 is involved in haem-precursor transport across the mitochondrial membrane. The crystal structure of its nucleotide-binding domain (NBD) has been determined in the apo form and in complexes with ADP, with ADP and Mg(2+) and with ATP at high resolution. The overall structure is L-shaped and consists of two lobes, consistent with other reported NBD structures. Nucleotide binding is mediated by the highly conserved Tyr599 and the Walker A motif, and induces notable structural changes. Structural comparison with other structurally characterized NBDs and full-length ABC transporters gives the first insight into the possible catalytic mechanism of ABCB6 and the role of the N-terminal helix alpha(1) in full-length ABCB6.
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Affiliation(s)
- Matthias Haffke
- Helmholtz Zentrum für Infektionsforschung, Braunschweig, Germany
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96
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Abstract
How ABC transporters work is a key issue because of their important roles in multidrug resistance of pathogenic bacteria, reduced efficacy of antitumor drugs, cholesterol metabolism, cell homeostasis and immune response. In the past few years, significant progress has been made in crystallization and structure determination of (mostly) bacterial ABC transporters, as well as in functional studies on ABC systems involved in human pathology. In this review, we use the transporter associated with antigen processing (TAP) to illustrate what is known regarding the mechanism of substrate transport. We also discuss the chemical basis of substrate recognition by TAP and the allosteric cross-talk between the binding of substrate, the release of chemical energy by ATP hydrolysis and cross-membrane translocation. Finally, we detail the role of TAP in a large macromolecular assembly, which optimally loads MHC class I molecules, and the interference with this machinery by TAP-targeted viral factors. Because of structural and probable mechanistic similarities, the understanding of the detailed structure and mechanism of TAP will be applicable to all ABC systems, including those of medical relevance.
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97
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Abstract
How ABC transporters work is a key issue because of their important roles in multidrug resistance of pathogenic bacteria, reduced efficacy of antitumor drugs, cholesterol metabolism, cell homeostasis and immune response. In the past few years, significant progress has been made in crystallization and structure determination of (mostly) bacterial ABC transporters, as well as in functional studies on ABC systems involved in human pathology. In this review, we use the transporter associated with antigen processing (TAP) to illustrate what is known regarding the mechanism of substrate transport. We also discuss the chemical basis of substrate recognition by TAP and the allosteric cross-talk between the binding of substrate, the release of chemical energy by ATP hydrolysis and cross-membrane translocation. Finally, we detail the role of TAP in a large macromolecular assembly, which optimally loads MHC class I molecules, and the interference with this machinery by TAP-targeted viral factors. Because of structural and probable mechanistic similarities, the understanding of the detailed structure and mechanism of TAP will be applicable to all ABC systems, including those of medical relevance.
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Affiliation(s)
- David Parcej
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Frankfurt, Germany.
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98
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Tsai MF, Li M, Hwang TC. Stable ATP binding mediated by a partial NBD dimer of the CFTR chloride channel. ACTA ACUST UNITED AC 2010; 135:399-414. [PMID: 20421370 PMCID: PMC2860585 DOI: 10.1085/jgp.201010399] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR), a member of the adenosine triphosphate (ATP) binding cassette (ABC) superfamily, is an ATP-gated chloride channel. Like other ABC proteins, CFTR encompasses two nucleotide binding domains (NBDs), NBD1 and NBD2, each accommodating an ATP binding site. It is generally accepted that CFTR's opening-closing cycles, each completed within 1 s, are driven by rapid ATP binding and hydrolysis events in NBD2. Here, by recording CFTR currents in real time with a ligand exchange protocol, we demonstrated that during many of these gating cycles, NBD1 is constantly occupied by a stably bound ATP or 8-N(3)-ATP molecule for tens of seconds. We provided evidence that this tightly bound ATP or 8-N(3)-ATP also interacts with residues in the signature sequence of NBD2, a telltale sign for an event occurring at the NBD1-NBD2 interface. The open state of CFTR has been shown to represent a two-ATP-bound NBD dimer. Our results indicate that upon ATP hydrolysis in NBD2, the channel closes into a "partial NBD dimer" state where the NBD interface remains partially closed, preventing ATP dissociation from NBD1 but allowing the release of hydrolytic products and binding of the next ATP to occur in NBD2. Opening and closing of CFTR can then be coupled to the formation and "partial" separation of the NBD dimer. The tightly bound ATP molecule in NBD1 can occasionally dissociate from the partial dimer state, resulting in a nucleotide-free monomeric state of NBDs. Our data, together with other structural/functional studies of CFTR's NBDs, suggest that this process is poorly reversible, implying that the channel in the partial dimer state or monomeric state enters the open state through different pathways. We therefore proposed a gating model for CFTR with two distinct cycles. The structural and functional significance of our results to other ABC proteins is discussed.
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Affiliation(s)
- Ming-Feng Tsai
- Department of Medical Pharmacology and Physiology and 2 Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA
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99
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Aittoniemi J, de Wet H, Ashcroft FM, Sansom MSP. Asymmetric switching in a homodimeric ABC transporter: a simulation study. PLoS Comput Biol 2010; 6:e1000762. [PMID: 20454684 PMCID: PMC2861673 DOI: 10.1371/journal.pcbi.1000762] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2009] [Accepted: 03/24/2010] [Indexed: 12/02/2022] Open
Abstract
ABC transporters are a large family of membrane proteins involved in a variety of cellular processes, including multidrug and tumor resistance and ion channel regulation. Advances in the structural and functional understanding of ABC transporters have revealed that hydrolysis at the two canonical nucleotide-binding sites (NBSs) is co-operative and non-simultaneous. A conserved core architecture of bacterial and eukaryotic ABC exporters has been established, as exemplified by the crystal structure of the homodimeric multidrug exporter Sav1866. Currently, it is unclear how sequential ATP hydrolysis arises in a symmetric homodimeric transporter, since it implies at least transient asymmetry at the NBSs. We show by molecular dynamics simulation that the initially symmetric structure of Sav1866 readily undergoes asymmetric transitions at its NBSs in a pre-hydrolytic nucleotide configuration. MgATP-binding residues and a network of charged residues at the dimer interface are shown to form a sequence of putative molecular switches that allow ATP hydrolysis only at one NBS. We extend our findings to eukaryotic ABC exporters which often consist of two non-identical half-transporters, frequently with degeneracy substitutions at one of their two NBSs. Interestingly, many residues involved in asymmetric conformational switching in Sav1866 are substituted in degenerate eukaryotic NBS. This finding strengthens recent suggestions that the interplay of a consensus and a degenerate NBS in eukaroytic ABC proteins pre-determines the sequence of hydrolysis at the two NBSs. ABC transporters are a large family of membrane proteins present in all organisms. Typically, they utilize ATP hydrolysis, the most prominent biological energy source, to translocate substrates into cells (e.g., bacterial nutritient uptake) or out of cells (e.g., multidrug exporters that contribute to antimicrobial resistance in bacteria and resistance to chemotherapeutic drugs in cancer). Also clinically relevant non-transport roles have been identified among ABC proteins. ABC transporters bind two molecules of ATP but do not hydrolyze them simultaneously. Therefore, an ABC transporter that consists of two symmetric halves must temporarily adopt asymmetric conformations at the two ATP-binding sites. Such transient conformational changes are difficult to address biochemically, but may be amenable to study by simulation methods, leading to future experiments. We employ molecular dynamics simulations to study how asymmetric switching might occur in the homodimeric bacterial ABC multidrug exporter Sav1866. The simulations suggest a mechanism of conformational switching that encompasses the ATP-binding sites and their interface towards the substrate-binding site. We extend our findings to show how asymmetric residue substitutions may render the switching process non-stochastic in mammalian Sav1866-like ABC exporters. This contributes to ongoing discussions about the role of two dissimilar ATP-binding sites in clinically relevant ABC proteins.
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Affiliation(s)
- Jussi Aittoniemi
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
- Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford, United Kingdom
| | - Heidi de Wet
- Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M. Ashcroft
- Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford, United Kingdom
| | - Mark S. P. Sansom
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
- * E-mail:
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100
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Atwell S, Brouillette CG, Conners K, Emtage S, Gheyi T, Guggino WB, Hendle J, Hunt JF, Lewis HA, Lu F, Protasevich II, Rodgers LA, Romero R, Wasserman SR, Weber PC, Wetmore D, Zhang FF, Zhao X. Structures of a minimal human CFTR first nucleotide-binding domain as a monomer, head-to-tail homodimer, and pathogenic mutant. Protein Eng Des Sel 2010; 23:375-84. [PMID: 20150177 DOI: 10.1093/protein/gzq004] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Upon removal of the regulatory insert (RI), the first nucleotide binding domain (NBD1) of human cystic fibrosis transmembrane conductance regulator (CFTR) can be heterologously expressed and purified in a form that remains stable without solubilizing mutations, stabilizing agents or the regulatory extension (RE). This protein, NBD1 387-646(Delta405-436), crystallizes as a homodimer with a head-to-tail association equivalent to the active conformation observed for NBDs from symmetric ATP transporters. The 1.7-A resolution X-ray structure shows how ATP occupies the signature LSGGQ half-site in CFTR NBD1. The DeltaF508 version of this protein also crystallizes as a homodimer and differs from the wild-type structure only in the vicinity of the disease-causing F508 deletion. A slightly longer construct crystallizes as a monomer. Comparisons of the homodimer structure with this and previously published monomeric structures show that the main effect of ATP binding at the signature site is to order the residues immediately preceding the signature sequence, residues 542-547, in a conformation compatible with nucleotide binding. These residues likely interact with a transmembrane domain intracellular loop in the full-length CFTR channel. The experiments described here show that removing the RI from NBD1 converts it into a well-behaved protein amenable to biophysical studies yielding deeper insights into CFTR function.
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Affiliation(s)
- Shane Atwell
- Eli Lilly & Co., 10300 Campus Point Drive, San Diego, CA 92121, USA
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