51
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El Hiani Y, Linsdell P. Role of the juxtamembrane region of cytoplasmic loop 3 in the gating and conductance of the cystic fibrosis transmembrane conductance regulator chloride channel. Biochemistry 2012; 51:3971-81. [PMID: 22545782 PMCID: PMC3381012 DOI: 10.1021/bi300065z] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Opening and closing of the cystic fibrosis transmembrane conductance regulator chloride channel are controlled by interactions of ATP with its cytoplasmic nucleotide binding domains (NBDs). The NBDs are connected to the transmembrane pore via four cytoplasmic loops. These loops have been suggested to play roles both in channel gating and in forming a cytoplasmic extension of the channel pore. To investigate the structure and function of one of these cytoplasmic loops, we have used patch clamp recording to investigate the accessibility of cytoplasmically applied cysteine-reactive reagents to cysteines introduced into loop 3. We find that methanethiosulfonate (MTS) reagents modify cysteines introduced at 14 of 16 sites studied in the juxtamembrane region of loop 3, in all cases leading to inhibition of channel function. In most cases, both the functional effects of modification and the rate of modification were similar for negatively and positively charged MTS reagents. Single-channel recordings indicated that, at all sites, inhibition was the result of an MTS reagent-induced decrease in channel open probability; in no case was the Cl(-) conductance of open channels altered by modification. These results indicate that loop 3 is readily accessible to the cytoplasm and support the involvement of this region in the control of channel gating. However, our results do not support the hypothesis that this region is close enough to the Cl(-) permeation pathway to exert any influence on permeating Cl(-) ions. We propose that either the cytoplasmic pore is very wide or cytoplasmic Cl(-) ions use other routes to access the transmembrane pore.
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Affiliation(s)
- Yassine El Hiani
- Department of Physiology and Biophysics, Dalhousie University , Halifax, Nova Scotia B3H 4R2, Canada
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52
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Abstract
Accumulation of all-trans-retinal (all-trans-RAL), reactive vitamin A aldehyde, is one of the key factors in initiating retinal photodamage. This photodamage is characterized by progressive retinal cell death evoked by light exposure in both an acute and chronic fashion. Photoactivated rhodopsin releases all-trans-RAL, which is subsequently transported by ATP-binding cassette transporter 4 and reduced to all-trans-retinol by all-trans-retinol dehydrogenases located in photoreceptor cells. Any interruptions in the clearing of all-trans-RAL in the photoreceptors can cause an accumulation of this reactive aldehyde and its toxic condensation products. This accumulation may result in the manifestation of retinal dystrophy including human retinal degenerative diseases such as Stargardt's disease and age-related macular degeneration. Herein, we discuss the mechanisms of all-trans-RAL clearance in photoreceptor cells by sequential enzymatic reactions, the visual (retinoid) cycle, and potential molecular pathways of retinal photodamage. We also review recent imaging technologies to monitor retinal health status as well as novel therapeutic strategies preventing all-trans-RAL-associated retinal photodamage.
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Affiliation(s)
- Tadao Maeda
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH, USA
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53
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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: 4.3] [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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54
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Greenfield LK, Whitfield C. Synthesis of lipopolysaccharide O-antigens by ABC transporter-dependent pathways. Carbohydr Res 2012; 356:12-24. [PMID: 22475157 DOI: 10.1016/j.carres.2012.02.027] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Revised: 02/23/2012] [Accepted: 02/24/2012] [Indexed: 01/10/2023]
Abstract
The O-polysaccharide (O-PS; O-antigen) of bacterial lipopolysaccharides is made up of repeating units of one or more sugar residues and displays remarkable structural diversity. Despite the structural variations, there are only three strategies for O-PS assembly. The ATP-binding cassette (ABC)-transporter-dependent mechanism of O-PS biosynthesis is widespread. The Escherichia coli O9a and Klebsiella pneumoniae O2a antigens provide prototypes, which are distinguished by the fine details that link glycan polymerization and chain termination at the cytoplasmic face of the inner membrane to its export via the ABC transporter. Here, we describe the current understanding of these processes. Since glycoconjugate assembly complexes that utilize an ABC transporter-dependent pathway are widespread among the bacterial kingdom, the models described here are expected to extend beyond O-PS biosynthesis systems.
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Affiliation(s)
- Laura K Greenfield
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
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55
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Elucidating the Biosynthetic Pathway for the Polyketide-Nonribosomal Peptide Collismycin A: Mechanism for Formation of the 2,2′-bipyridyl Ring. ACTA ACUST UNITED AC 2012; 19:399-413. [DOI: 10.1016/j.chembiol.2012.01.014] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2011] [Revised: 01/13/2012] [Accepted: 01/17/2012] [Indexed: 11/22/2022]
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56
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Wang W, Linsdell P. Alternating access to the transmembrane domain of the ATP-binding cassette protein cystic fibrosis transmembrane conductance regulator (ABCC7). J Biol Chem 2012; 287:10156-10165. [PMID: 22303012 DOI: 10.1074/jbc.m112.342972] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is a member of the ATP-binding cassette (ABC) protein family, most members of which act as active transporters. Actively transporting ABC proteins are thought to alternate between "outwardly facing" and "inwardly facing" conformations of the transmembrane substrate pathway. In CFTR, it is assumed that the outwardly facing conformation corresponds to the channel open state, based on homology with other ABC proteins. We have used patch clamp recording to quantify the rate of access of cysteine-reactive probes to cysteines introduced into two different transmembrane regions of CFTR from both the intracellular and extracellular solutions. Two probes, the large [2-sulfonatoethyl]methanethiosulfonate (MTSES) molecule and permeant Au(CN)(2)(-) ions, were applied to either side of the membrane to modify cysteines substituted for Leu-102 (first transmembrane region) and Thr-338 (sixth transmembrane region). Channel opening and closing were altered by mutations in the nucleotide binding domains of the channel. We find that, for both MTSES and Au(CN)(2)(-), access to these two cysteines from the cytoplasmic side is faster in open channels, whereas access to these same sites from the extracellular side is faster in closed channels. These results are consistent with alternating access to the transmembrane regions, however with the open state facing inwardly and the closed state facing outwardly. Our findings therefore prompt revision of current CFTR structural and mechanistic models, as well as having broader implications for transport mechanisms in all ABC proteins. Our results also suggest possible locations of both functional and dysfunctional ("vestigial") gates within the CFTR permeation pathway.
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Affiliation(s)
- Wuyang Wang
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
| | - Paul Linsdell
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
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57
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Kubeš M, Yang H, Richter GL, Cheng Y, Młodzińska E, Wang X, Blakeslee JJ, Carraro N, Petrášek J, Zažímalová E, Hoyerová K, Peer WA, Murphy AS. The Arabidopsis concentration-dependent influx/efflux transporter ABCB4 regulates cellular auxin levels in the root epidermis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2012; 69:640-54. [PMID: 21992190 DOI: 10.1111/j.1365-313x.2011.04818.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Arabidopsis ATP-binding cassette B4 (ABCB4) is a root-localised auxin efflux transporter with reported auxin uptake activity in low auxin concentrations. Results reported here demonstrate that ABCB4 is a substrate-activated regulator of cellular auxin levels. The contribution of ABCB4 to shootward auxin movement at the root apex increases with auxin concentration, but in root hair elongation assays ABCB4-mediated uptake is evident at low concentrations as well. Uptake kinetics of ABCB4 heterologously expressed in Schizosaccharomyces pombe differed from the saturation kinetics of AUX1 as uptake converted to efflux at threshold indole-3-acetic acid (IAA) concentrations. The concentration dependence of ABCB4 appears to be a direct effect on transporter activity, as ABCB4 expression and ABCB4 plasma membrane (PM) localisation at the root apex are relatively insensitive to changes in auxin concentration. However, PM localization of ABCB4 decreases with 1-naphthylphthalamic acid (NPA) treatment. Unlike other plant ABCBs studied to date, and consistent with decreased detergent solubility, ABCB4(pro) :ABCB4-GFP is partially internalised in all cell types by 0.05% DMSO, but not 0.1% ethanol. In trichoblasts, ABCB4(pro) :ABCB4-GFP PM signals are reduced by >200 nm IAA and 2,4-dichlorophenoxyacetic acid (2,4-D). In heterologous systems and in planta, ABCB4 transports benzoic acid with weak affinity, but not the oxidative catabolism products 2-oxindole-3-acetic-acid and 2-oxindole-3-acetyl-β-D-glucose. ABCB4 mediates uptake, but not efflux, of the synthetic auxin 2,4-D in cells lacking AUX1 activity. Results presented here suggest that 2,4-D is a non-competitive inhibitor of IAA transport by ABCB4 and indicate that ABCB4 is a target of 2,4-D herbicidal activity.
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Affiliation(s)
- Martin Kubeš
- Institute of Experimental Botany, the Academy of Sciences of the Czech Republic, Rozvojová 263, CZ-165 02 Prague 6, Czech Republic
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58
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Wang W, Linsdell P. Conformational change opening the CFTR chloride channel pore coupled to ATP-dependent gating. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:851-60. [PMID: 22234285 DOI: 10.1016/j.bbamem.2011.12.025] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2011] [Revised: 12/21/2011] [Accepted: 12/23/2011] [Indexed: 12/13/2022]
Abstract
Opening and closing of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel are controlled by ATP binding and hydrolysis by its nucleotide binding domains (NBDs). This is presumed to control opening of a single "gate" within the permeation pathway, however, the location of such a gate has not been described. We used patch clamp recording to monitor access of cytosolic cysteine reactive reagents to cysteines introduced into different transmembrane (TM) regions in a cysteine-less form of CFTR. The rate of modification of Q98C (TM1) and I344C (TM6) by both [2-sulfonatoethyl] methanethiosulfonate (MTSES) and permeant Au(CN)(2)(-) ions was reduced when ATP concentration was reduced from 1mM to 10μM, and modification by MTSES was accelerated when 2mM pyrophosphate was applied to prevent channel closure. Modification of K95C (TM1) and V345C (TM6) was not affected by these manoeuvres. We also manipulated gating by introducing the mutations K464A (in NBD1) and E1371Q (in NBD2). The rate of modification of Q98C and I344C by both MTSES and Au(CN)(2)(-) was decreased by K464A and increased by E1371Q, whereas modification of K95C and V345C was not affected. These results suggest that access from the cytoplasm to K95 and V345 is similar in open and closed channels. In contrast, modifying ATP-dependent channel gating alters access to Q98 and I344, located further into the pore. We propose that ATP-dependent gating of CFTR is associated with the opening and closing of a gate within the permeation pathway at the level of these pore-lining amino acids.
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Affiliation(s)
- Wuyang Wang
- Department of Physiology and Biophysics, Dalhousie University, Nova Scotia, Canada
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59
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Verhalen B, Ernst S, Börsch M, Wilkens S. Dynamic ligand-induced conformational rearrangements in P-glycoprotein as probed by fluorescence resonance energy transfer spectroscopy. J Biol Chem 2011; 287:1112-27. [PMID: 22086917 DOI: 10.1074/jbc.m111.301192] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
P-glycoprotein (Pgp), a member of the ATP-binding cassette transporter family, functions as an ATP hydrolysis-driven efflux pump to rid the cell of toxic organic compounds, including a variety of drugs used in anticancer chemotherapy. Here, we used fluorescence resonance energy transfer (FRET) spectroscopy to delineate the structural rearrangements the two nucleotide binding domains (NBDs) are undergoing during the catalytic cycle. Pairs of cysteines were introduced into equivalent regions in the N- and C-terminal NBDs for labeling with fluorescent dyes for ensemble and single-molecule FRET spectroscopy. In the ensemble FRET, a decrease of the donor to acceptor (D/A) ratio was observed upon addition of drug and ATP. Vanadate trapping further decreased the D/A ratio, indicating close association of the two NBDs. One of the cysteine mutants was further analyzed using confocal single-molecule FRET spectroscopy. Single Pgp molecules showed fast fluctuations of the FRET efficiencies, indicating movements of the NBDs on a time scale of 10-100 ms. Populations of low, medium, and high FRET efficiencies were observed during drug-stimulated MgATP hydrolysis, suggesting the presence of at least three major conformations of the NBDs during catalysis. Under conditions of vanadate trapping, most molecules displayed high FRET efficiency states, whereas with cyclosporin, more molecules showed low FRET efficiency. Different dwell times of the FRET states were found for the distinct biochemical conditions, with the fastest movements during active turnover. The FRET spectroscopy observations are discussed in context of a model of the catalytic mechanism of Pgp.
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Affiliation(s)
- Brandy Verhalen
- Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, New York 13210, USA
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60
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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: 0.2] [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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61
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Membrane Transport Protein ABCA1 and Type 2 Diabetes Mellitus*. PROG BIOCHEM BIOPHYS 2011. [DOI: 10.3724/sp.j.1206.2010.00536] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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62
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Rosenberg MF, O'Ryan LP, Hughes G, Zhao Z, Aleksandrov LA, Riordan JR, Ford RC. The cystic fibrosis transmembrane conductance regulator (CFTR): three-dimensional structure and localization of a channel gate. J Biol Chem 2011; 286:42647-42654. [PMID: 21931164 PMCID: PMC3234965 DOI: 10.1074/jbc.m111.292268] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Cystic fibrosis affects about 1 in 2500 live births and involves loss of transmembrane chloride flux due to a lack of a membrane protein channel termed the cystic fibrosis transmembrane conductance regulator (CFTR). We have studied CFTR structure by electron crystallography. The data were compared with existing structures of other ATP-binding cassette transporters. The protein was crystallized in the outward facing state and resembled the well characterized Sav1866 transporter. We identified regions in the CFTR map, not accounted for by Sav1866, which were potential locations for the regulatory region as well as the channel gate. In this analysis, we were aided by the fact that the unit cell was composed of two molecules not related by crystallographic symmetry. We also identified regions in the fitted Sav1866 model that were missing from the map, hence regions that were either disordered in CFTR or differently organized compared with Sav1866. Apart from the N and C termini, this indicated that in CFTR, the cytoplasmic end of transmembrane helix 5/11 and its associated loop could be partly disordered (or alternatively located).
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Affiliation(s)
- Mark F Rosenberg
- Faculty of Life Sciences, University of Manchester, Manchester Interdisciplinary Biocentre, Manchester M1 7DN, United Kingdom
| | - Liam P O'Ryan
- Faculty of Life Sciences, University of Manchester, Manchester Interdisciplinary Biocentre, Manchester M1 7DN, United Kingdom
| | - Guy Hughes
- Faculty of Life Sciences, University of Manchester, Manchester Interdisciplinary Biocentre, Manchester M1 7DN, United Kingdom
| | - Zhefeng Zhao
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Luba A Aleksandrov
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599
| | - John R Riordan
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Robert C Ford
- Faculty of Life Sciences, University of Manchester, Manchester Interdisciplinary Biocentre, Manchester M1 7DN, United Kingdom.
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63
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Lau SK, Fan RY, Wong GK, Teng JL, Sze KH, Tse H, Yuen KY, Woo PC. Transport genes and chemotaxis in Laribacter hongkongensis: a genome-wide analysis. Cell Biosci 2011; 1:28. [PMID: 21849034 PMCID: PMC3180692 DOI: 10.1186/2045-3701-1-28] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Accepted: 08/17/2011] [Indexed: 01/27/2023] Open
Abstract
Background Laribacter hongkongensis is a Gram-negative, sea gull-shaped rod associated with community-acquired gastroenteritis. The bacterium has been found in diverse freshwater environments including fish, frogs and drinking water reservoirs. Using the complete genome sequence data of L. hongkongensis, we performed a comprehensive analysis of putative transport-related genes and genes related to chemotaxis, motility and quorum sensing, which may help the bacterium adapt to the changing environments and combat harmful substances. Results A genome-wide analysis using Transport Classification Database TCDB, similarity and keyword searches revealed the presence of a large diversity of transporters (n = 457) and genes related to chemotaxis (n = 52) and flagellar biosynthesis (n = 40) in the L. hongkongensis genome. The transporters included those from all seven major transporter categories, which may allow the uptake of essential nutrients or ions, and extrusion of metabolic end products and hazardous substances. L. hongkongensis is unique among closely related members of Neisseriaceae family in possessing higher number of proteins related to transport of ammonium, urea and dicarboxylate, which may reflect the importance of nitrogen and dicarboxylate metabolism in this assacharolytic bacterium. Structural modeling of two C4-dicarboxylate transporters showed that they possessed similar structures to the determined structures of other DctP-TRAP transporters, with one having an unusual disulfide bond. Diverse mechanisms for iron transport, including hemin transporters for iron acquisition from host proteins, were also identified. In addition to the chemotaxis and flagella-related genes, the L. hongkongensis genome also contained two copies of qseB/qseC homologues of the AI-3 quorum sensing system. Conclusions The large number of diverse transporters and genes involved in chemotaxis, motility and quorum sensing suggested that the bacterium may utilize a complex system to adapt to different environments. Structural modeling will provide useful insights on the transporters in L. hongkongensis.
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Affiliation(s)
- Susanna Kp Lau
- State Key Laboratory of Emerging Infectious Diseases, Hong Kong.,Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong.,Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong.,Department of Microbiology, The University of Hong Kong, Hong Kong
| | - Rachel Yy Fan
- Department of Microbiology, The University of Hong Kong, Hong Kong
| | - Gilman Km Wong
- Department of Microbiology, The University of Hong Kong, Hong Kong
| | - Jade Ll Teng
- Department of Microbiology, The University of Hong Kong, Hong Kong
| | - Kong-Hung Sze
- Department of Chemistry, The University of Hong Kong, Hong Kong
| | - Herman Tse
- State Key Laboratory of Emerging Infectious Diseases, Hong Kong.,Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong.,Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong.,Department of Microbiology, The University of Hong Kong, Hong Kong
| | - Kwok-Yung Yuen
- State Key Laboratory of Emerging Infectious Diseases, Hong Kong.,Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong.,Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong.,Department of Microbiology, The University of Hong Kong, Hong Kong
| | - Patrick Cy Woo
- State Key Laboratory of Emerging Infectious Diseases, Hong Kong.,Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong.,Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong.,Department of Microbiology, The University of Hong Kong, Hong Kong
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64
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Functional arrangement of the 12th transmembrane region in the CFTR chloride channel pore based on functional investigation of a cysteine-less CFTR variant. Pflugers Arch 2011; 462:559-71. [PMID: 21796338 DOI: 10.1007/s00424-011-0998-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2011] [Revised: 06/27/2011] [Accepted: 07/15/2011] [Indexed: 12/25/2022]
Abstract
The membrane-spanning part of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel comprises 12 transmembrane (TM) α-helices, arranged into two pseudo-symmetrical groups of six. While TM6 in the N-terminal TMs is known to line the pore and to make an important contribution to channel properties, much less is known about its C-terminal counterpart, TM12. We have used patch clamp recording to investigate the accessibility of cytoplasmically applied cysteine-reactive reagents to cysteines introduced along the length of TM12 in a cysteine-less variant of CFTR. We find that methanethiosulfonate (MTS) reagents irreversibly modify cysteines substituted for TM12 residues N1138, M1140, S1141, T1142, Q1144, W1145, V1147, N1148, and S1149 when applied to the cytoplasmic side of open channels. Cysteines sensitive to internal MTS reagents were not modified by extracellular [2-(trimethylammonium)ethyl] MTS, consistent with MTS reagent impermeability. Both S1141C and T1142C could be modified by intracellular [2-sulfonatoethyl] MTS prior to channel activation; however, N1138C and M1140C, located deeper into the pore from its cytoplasmic end, were modified only after channel activation. Comparison of these results with previous work on CFTR-TM6 allows us to develop a model of the relative positions, functional contributions, and alignment of these two important TMs lining the CFTR pore. We also propose a mechanism by which these seemingly structurally symmetrical TMs make asymmetric contributions to the functional properties of the channel pore.
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65
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Fodale V, Pierobon M, Liotta L, Petricoin E. Mechanism of cell adaptation: when and how do cancer cells develop chemoresistance? Cancer J 2011; 17:89-95. [PMID: 21427552 DOI: 10.1097/ppo.0b013e318212dd3d] [Citation(s) in RCA: 141] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Chemotherapy treatments are considered essential tools to defeat cancer progression and dissemination to improve patients' quality of life and survival. Although most malignancies initially respond to chemotherapeutic treatments, after an unpredictable period, tumor cells develop mechanisms of resistance to the treatment. Different cell compartments are involved in the mechanism of chemoresistance, and multiple mechanisms can be activated by single cells at different times of the cancer progression. Alteration of drug metabolism, derangement of intracellular pathways' signaling, cross-talk between different membrane receptors, and modification of apoptotic signaling and interference with cell replication are all mechanisms that the cell uses to overcome the effect of pharmacological compounds.In this review, we describe different adaptation, mostly at the level of the proteome, which cancer cells use to develop resistance to cancer treatment.
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Affiliation(s)
- Valentina Fodale
- Center for Applied Proteomics and Molecular Medicine, George Mason University, Manassas, VA, USA
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66
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Malbruny B, Werno AM, Murdoch DR, Leclercq R, Cattoir V. Cross-resistance to lincosamides, streptogramins A, and pleuromutilins due to the lsa(C) gene in Streptococcus agalactiae UCN70. Antimicrob Agents Chemother 2011; 55:1470-4. [PMID: 21245447 PMCID: PMC3067124 DOI: 10.1128/aac.01068-10] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 12/14/2010] [Accepted: 01/08/2011] [Indexed: 01/31/2023] Open
Abstract
Streptococcus agalactiae UCN70, isolated from a vaginal swab obtained in New Zealand, is resistant to lincosamides and streptogramins A (LS(A) phenotype) and also to tiamulin (a pleuromutilin). By whole-genome sequencing, we identified a 5,224-bp chromosomal extra-element that comprised a 1,479-bp open reading frame coding for an ABC protein (492 amino acids) 45% identical to Lsa(A), a protein related to intrinsic LS(A) resistance in Enterococcus faecalis. Expression of this novel gene, named lsa(C), in S. agalactiae BM132 after cloning led to an increase in MICs of lincomycin (0.06 to 4 μg/ml), clindamycin (0.03 to 2 μg/ml), dalfopristin (2 to >32 μg/ml), and tiamulin (0.12 to 32 μg/ml), whereas no change in MICs of erythromycin (0.06 μg/ml), azithromycin (0.03 μg/ml), spiramycin (0.25 μg/ml), telithromycin (0.03 μg/ml), and quinupristin (8 μg/ml) was observed. The phenotype was renamed the LS(A)P phenotype on the basis of cross-resistance to lincosamides, streptogramins A, and pleuromutilins. This gene was also identified in similar genetic environments in 17 other S. agalactiae clinical isolates from New Zealand exhibiting the same LS(A)P phenotype, whereas it was absent in susceptible S. agalactiae strains. Interestingly, this extra-element was bracketed by a 7-bp duplication of a target site (ATTAGAA), suggesting that this structure was likely a mobile genetic element. In conclusion, we identified a novel gene, lsa(C), responsible for the acquired LS(A)P resistance phenotype in S. agalactiae. Dissection of the biochemical basis of resistance, as well as demonstration of in vitro mobilization of lsa(C), remains to be performed.
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Affiliation(s)
- Brigitte Malbruny
- Service de Microbiologie and EA 2128, Relations Hôte et Microorganismes des Épithéliums, Hôpital Côte de Nacre, Université de Caen Basse-Normandie, Caen, France, Microbiology Unit, Canterbury Health Laboratories and University of Otago, Christchurch, New Zealand
| | - Anja M. Werno
- Service de Microbiologie and EA 2128, Relations Hôte et Microorganismes des Épithéliums, Hôpital Côte de Nacre, Université de Caen Basse-Normandie, Caen, France, Microbiology Unit, Canterbury Health Laboratories and University of Otago, Christchurch, New Zealand
| | - David R. Murdoch
- Service de Microbiologie and EA 2128, Relations Hôte et Microorganismes des Épithéliums, Hôpital Côte de Nacre, Université de Caen Basse-Normandie, Caen, France, Microbiology Unit, Canterbury Health Laboratories and University of Otago, Christchurch, New Zealand
| | - Roland Leclercq
- Service de Microbiologie and EA 2128, Relations Hôte et Microorganismes des Épithéliums, Hôpital Côte de Nacre, Université de Caen Basse-Normandie, Caen, France, Microbiology Unit, Canterbury Health Laboratories and University of Otago, Christchurch, New Zealand
| | - Vincent Cattoir
- Service de Microbiologie and EA 2128, Relations Hôte et Microorganismes des Épithéliums, Hôpital Côte de Nacre, Université de Caen Basse-Normandie, Caen, France, Microbiology Unit, Canterbury Health Laboratories and University of Otago, Christchurch, New Zealand
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67
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Abstract
CFTR is a member of the ATP-binding cassette family of membrane proteins. This is one of the best characterised membrane protein families in terms of structure and function. CFTR operates as an ion channel, unlike nearly all other family members which are active transporters. Here, we discuss methods that have allowed such data to be obtained for CFTR.
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Affiliation(s)
- Robert C Ford
- Faculty of Life Sciences, Manchester Interdisciplinary Biocentre, The University of Manchester, Manchester, UK.
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68
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Shaikh S, Wen PC, Enkavi G, Huang Z, Tajkhorshid E. Capturing Functional Motions of Membrane Channels and Transporters with Molecular Dynamics Simulation. JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE 2010; 7:2481-2500. [PMID: 23710155 PMCID: PMC3661405 DOI: 10.1166/jctn.2010.1636] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Conformational changes of proteins are involved in all aspects of protein function in biology. Almost all classes of proteins respond to changes in their environment, ligand binding, and interaction with other proteins and regulatory agents through undergoing conformational changes of various degrees and magnitudes. Membrane channels and transporters are the major classes of proteins that are responsible for mediating efficient and selective transport of materials across the cellular membrane. Similar to other proteins, they take advantage of conformational changes to make transitions between various functional states. In channels, large-scale conformational changes are mostly involved in the process of "gating", i.e., opening and closing of the pore of the channel protein in response to various signals. In transporters, conformational changes constitute various steps of the conduction process, and, thus, are more closely integrated in the transport process. Owing to significant progress in developing highly efficient parallel algorithms in molecular dynamics simulations and increased computational resources, and combined with the availability of high-resolution, atomic structures of membrane proteins, we are in an unprecedented position to use computer simulation and modeling methodologies to investigate the mechanism of function of membrane channels and transporters. While the entire transport cycle is still out of reach of current methodologies, many steps involved in the function of transport proteins have been characterized with molecular dynamics simulations. Here, we present several examples of such studies from our laboratory, in which functionally relevant conformational changes of membrane channels and transporters have been characterized using extended simulations.
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Affiliation(s)
- Saher Shaikh
- Department of Biochemistry, Beckman Institute, and Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, U.S.A
| | - Po-Chao Wen
- Department of Biochemistry, Beckman Institute, and Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, U.S.A
| | - Giray Enkavi
- Department of Biochemistry, Beckman Institute, and Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, U.S.A
| | - Zhijian Huang
- Department of Biochemistry, Beckman Institute, and Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, U.S.A
| | - Emad Tajkhorshid
- Department of Biochemistry, Beckman Institute, and Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, U.S.A
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69
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Dynamics of alpha-helical subdomain rotation in the intact maltose ATP-binding cassette transporter. Proc Natl Acad Sci U S A 2010; 107:20293-8. [PMID: 21059948 DOI: 10.1073/pnas.1006544107] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
ATP-binding cassette (ABC) transporters are powered by a nucleotide-binding domain dimer that opens and closes during cycles of ATP hydrolysis. These domains consist of a RecA-like subdomain and an α-helical subdomain that is specific to the family. Many studies on isolated domains suggest that the helical subdomain rotates toward the RecA-like subdomain in response to ATP binding, moving the family signature motif into a favorable position to interact with the nucleotide across the dimer interface. Moreover, the transmembrane domains are docked into a cleft at the interface between these subdomains, suggesting a putative role of the rotation in interdomain communication. Electron paramagnetic resonance spectroscopy was used to study the dynamics of this rotation in the intact Escherichia coli maltose transporter MalFGK(2). This importer requires a periplasmic maltose-binding protein (MBP) that activates ATP hydrolysis by promoting the closure of the cassette dimer (MalK(2)). Whereas this rotation occurred during the transport cycle, it required not only trinucleotide, but also MBP, suggesting it is part of a global conformational change in the transporter. Interaction of AMP-PNP-Mg(2+) and a MBP that is locked in a closed conformation induced a transition from open MalK(2) to semiopen MalK(2) without significant subdomain rotation. Inward rotation of the helical subdomain and complete closure of MalK(2) therefore appear to be coupled to the reorientation of transmembrane helices and the opening of MBP, events that promote transfer of maltose into the transporter. After ATP hydrolysis, the helical subdomain rotates out as MalK(2) opens, resetting the transporter in an inward-facing conformation.
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70
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Xiong J, Feng L, Yuan D, Fu C, Miao W. Genome-wide identification and evolution of ATP-binding cassette transporters in the ciliate Tetrahymena thermophila: A case of functional divergence in a multigene family. BMC Evol Biol 2010; 10:330. [PMID: 20977778 PMCID: PMC2984421 DOI: 10.1186/1471-2148-10-330] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2010] [Accepted: 10/27/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In eukaryotes, ABC transporters that utilize the energy of ATP hydrolysis to expel cellular substrates into the environment are responsible for most of the efflux from cells. Many members of the superfamily of ABC transporters have been linked with resistance to multiple drugs or toxins. Owing to their medical and toxicological importance, members of the ABC superfamily have been studied in several model organisms and warrant examination in newly sequenced genomes. RESULTS A total of 165 ABC transporter genes, constituting a highly expanded superfamily relative to its size in other eukaryotes, were identified in the macronuclear genome of the ciliate Tetrahymena thermophila. Based on ortholog comparisons, phylogenetic topologies and intron characterizations, each highly expanded ABC transporter family of T. thermophila was classified into several distinct groups, and hypotheses about their evolutionary relationships are presented. A comprehensive microarray analysis revealed divergent expression patterns among the members of the ABC transporter superfamily during different states of physiology and development. Many of the relatively recently formed duplicate pairs within individual ABC transporter families exhibit significantly different expression patterns. Further analysis showed that multiple mechanisms have led to functional divergence that is responsible for the preservation of duplicated genes. CONCLUSION Gene duplications have resulted in an extensive expansion of the superfamily of ABC transporters in the Tetrahymena genome, making it the largest example of its kind reported in any organism to date. Multiple independent duplications and subsequent divergence contributed to the formation of different families of ABC transporter genes. Many of the members within a gene family exhibit different expression patterns. The combination of gene duplication followed by both sequence divergence and acquisition of new patterns of expression likely plays a role in the adaptation of Tetrahymen a to its environment.
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Affiliation(s)
- Jie Xiong
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, PR China
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71
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Ni Z, Bikadi Z, Rosenberg MF, Mao Q. Structure and function of the human breast cancer resistance protein (BCRP/ABCG2). Curr Drug Metab 2010; 11:603-17. [PMID: 20812902 DOI: 10.2174/138920010792927325] [Citation(s) in RCA: 189] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Accepted: 08/13/2010] [Indexed: 12/22/2022]
Abstract
The human breast cancer resistance protein (BCRP/ABCG2) is the second member of the G subfamily of the large ATP-binding cassette (ABC) transporter superfamily. BCRP was initially discovered in multidrug resistant breast cancer cell lines where it confers resistance to chemotherapeutic agents such as mitoxantrone, topotecan and methotrexate by extruding these compounds out of the cell. BCRP is capable of transporting non-chemotherapy drugs and xenobiotiocs as well, including nitrofurantoin, prazosin, glyburide, and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine. BCRP is frequently detected at high levels in stem cells, likely providing xenobiotic protection. BCRP is also highly expressed in normal human tissues including the small intestine, liver, brain endothelium, and placenta. Therefore, BCRP has been increasingly recognized for its important role in the absorption, elimination, and tissue distribution of drugs and xenobiotics. At present, little is known about the transport mechanism of BCRP, particularly how it recognizes and transports a large number of structurally and chemically unrelated drugs and xenobiotics. Here, we review current knowledge of structure and function of this medically important ABC efflux drug transporter.
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Affiliation(s)
- Zhanglin Ni
- Department of Pharmaceutics, School of Pharmacy, University of Washington, Health Science Building H272, 1959 NE Pacific Street, Seattle, Washington 98195-7610, USA
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72
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Zhang L, Aleksandrov LA, Riordan JR, Ford RC. Domain location within the cystic fibrosis transmembrane conductance regulator protein investigated by electron microscopy and gold labelling. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:399-404. [PMID: 20727849 DOI: 10.1016/j.bbamem.2010.08.012] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2010] [Revised: 08/13/2010] [Accepted: 08/13/2010] [Indexed: 11/25/2022]
Abstract
The domain organisation of the cystic fibrosis transmembrane conductance regulator (CFTR) protein was studied using electron microscopy of detergent-solubilised dimeric complexes. Ni-NTA nanogold labelling data suggest that in the nonphosphorylated, nucleotide-free state, the C-terminus is intimately associated with the cytoplasmic ATP-binding regions, whilst part of the regulatory domain occupies a position close to the cytoplasmic surface of the lipid membrane. Removal of the entire second nucleotide binding domain (NBD2) results in a deficit in the CFTR structure that is consistent with the size and shape of a single NBD. The data suggest that NBD2 lies closer to the C2 symmetry axis than the first nucleotide binding domain (NBD1) and that NBD2 from one CFTR monomer also contacts NBD1 from the opposing one. These data suggest that current homology models for CFTR based on other ATP-binding cassette proteins appear to be reasonable, at least to low resolution. We also find that Ni-NTA nanogold labelling of an internal hexa-Histidine sequence is a valuable approach to locate individual protein domains.
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Affiliation(s)
- Liang Zhang
- Faculty of Life Sciences, The University of Manchester, MIB, 131 Princess St., Manchester M1 7DN, UK
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73
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El Hiani Y, Linsdell P. Changes in accessibility of cytoplasmic substances to the pore associated with activation of the cystic fibrosis transmembrane conductance regulator chloride channel. J Biol Chem 2010; 285:32126-40. [PMID: 20675380 DOI: 10.1074/jbc.m110.113332] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Opening of the cystic fibrosis transmembrane conductance regulator Cl(-) channel is dependent both on phosphorylation and on ATP binding and hydrolysis. However, the mechanisms by which these cytoplasmic regulatory factors open the Cl(-) channel pore are not known. We have used patch clamp recording to investigate the accessibility of cytoplasmically applied cysteine-reactive reagents to cysteines introduced along the length of the pore-lining sixth transmembrane region (TM6) of a cysteine-less variant of cystic fibrosis transmembrane conductance regulator. We find that methanethiosulfonate (MTS) reagents modify irreversibly cysteines substituted for TM6 residues Phe-337, Thr-338, Ser-341, Ile-344, Val-345, Met-348, Ala-349, Arg-352, and Gln-353 when applied to the cytoplasmic side of open channels. However, the apparent rate of modification by internal [2-sulfonatoethyl] methanethiosulfonate (MTSES), a negatively charged MTS reagent, is dependent on the activation state of the channels. In particular, cysteines introduced far along the axis of TM6 from the inside (T338C, S341C, I344C) showed no evidence of significant modification even after prolonged pretreatment of non-activated channels with internal MTSES. In contrast, cysteines introduced closer to the inside of TM6 (V345C, M348C) were readily modified in both activated and non-activated channels. Access of a permeant anion, Au(CN)(2)(-), to T338C was similarly dependent upon channel activation state. The pattern of MTS modification we observe allows us to designate different pore-lining amino acid side chains to distinct functional regions of the channel pore. One logical interpretation of these findings is that cytoplasmic access to residues at the narrowest region of the pore changes concomitant with activation.
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Affiliation(s)
- Yassine El Hiani
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada
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74
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Molday RS, Zhang K. Defective lipid transport and biosynthesis in recessive and dominant Stargardt macular degeneration. Prog Lipid Res 2010; 49:476-92. [PMID: 20633576 DOI: 10.1016/j.plipres.2010.07.002] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Stargardt disease is a common inherited macular degeneration characterized by a significant loss in central vision in the first or second decade of life, bilateral atrophic changes in the central retina associated with degeneration of photoreceptors and underlying retinal pigment epithelial cells, and the presence of yellow flecks extending from the macula. Autosomal recessive Stargardt disease, the most common macular dystrophy, is caused by mutations in the gene encoding ABCA4, a photoreceptor ATP binding cassette (ABC) transporter. Biochemical studies together with analysis of abca4 knockout mice and Stargardt patients have implicated ABCA4 as a lipid transporter that facilitates the removal of potentially toxic retinal compounds from photoreceptors following photoexcitation. An autosomal dominant form of Stargardt disease also known as Stargardt-like dystrophy is caused by mutations in a gene encoding ELOVL4, an enzyme that catalyzes the elongation of very long-chain fatty acids in photoreceptors and other tissues. This review focuses on the molecular characterization of ABCA4 and ELOVL4 and their role in photoreceptor cell biology and the pathogenesis of Stargardt disease.
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Affiliation(s)
- Robert S Molday
- Department of Biochemistry and Molecular Biology, Centre of Macular Research, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, Canada.
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75
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Tsybovsky Y, Molday RS, Palczewski K. The ATP-binding cassette transporter ABCA4: structural and functional properties and role in retinal disease. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 703:105-25. [PMID: 20711710 DOI: 10.1007/978-1-4419-5635-4_8] [Citation(s) in RCA: 131] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
ATP-binding cassette transporters (ABC transporters) utilize the energy of ATP hydrolysis to translocate an unusually diverse set of substrates across cellular membranes. ABCA4, also known as ABCR, is a approximately 250 kDa single-chain ABC transporter localized to the disk margins of vertebrate photoreceptor outer segments. It is composed of two symmetrically organized halves, each comprising six membrane-spanning helices, a large glycosylated exocytoplasmic domain located inside the disk, and a cytoplasmic domain with an ATP-binding cassette. Hundreds of mutations in ABCA4 are known to cause impaired vision and blindness such as in Stargardt disease as well as related disorders. Biochemical and animal model studies in combination with patient analyses suggest that the natural substrate of ABCA4 is retinylidene-phosphatidylethanolamine (N-retinylidene-PE), a precursor of potentially toxic diretinal compounds. ABCA4 prevents accumulation of N-retinylidene-PE inside the disks by transporting it to the cytoplasmic side of the disk membrane where it can dissociate, allowing the released all-trans-retinal to enter the visual cycle. The pathogenesis of diseases caused by mutations in ABCA4 is complex, comprising a loss-of-function component as well as photoreceptor stress caused by protein mislocalization and misfolding.
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Affiliation(s)
- Yaroslav Tsybovsky
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH, USA.
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76
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Mornon JP, Lehn P, Callebaut I. Molecular models of the open and closed states of the whole human CFTR protein. Cell Mol Life Sci 2009; 66:3469-86. [PMID: 19707853 PMCID: PMC11115851 DOI: 10.1007/s00018-009-0133-0] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2009] [Revised: 07/17/2009] [Accepted: 08/12/2009] [Indexed: 12/15/2022]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR), involved in cystic fibrosis (CF), is a chloride channel belonging to the ATP-binding cassette (ABC) superfamily. Using the experimental structure of Sav1866 as template, we previously modeled the human CFTR structure, including membrane-spanning domains (MSD) and nucleotide-binding domains (NBD), in an outward-facing conformation (open channel state). Here, we constructed a model of the CFTR inward-facing conformation (closed channel) on the basis of the recent corrected structures of MsbA and compared the structural features of those two states of the channel. Interestingly, the MSD:NBD coupling interfaces including F508 (DeltaF508 being the most common CF mutation) are mainly left unchanged. This prediction, completed by the modeling of the regulatory R domain, is supported by experimental data and provides a molecular basis for a better understanding of the functioning of CFTR, especially of the structural features that make CFTR the unique channel among the ABC transporters.
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Affiliation(s)
- Jean-Paul Mornon
- IMPMC, UMR7590, CNRS, Universités Pierre et Marie Curie-Paris 6 et Denis Diderot-Paris 7, 140 rue de Lourmel, Paris, France
| | - Pierre Lehn
- INSERM U613, IFR148 ScInBioS, Université de Bretagne Occidentale, Brest, France
| | - Isabelle Callebaut
- IMPMC, UMR7590, CNRS, Universités Pierre et Marie Curie-Paris 6 et Denis Diderot-Paris 7, 140 rue de Lourmel, Paris, France
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