51
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Rodríguez-Casado A, Molina M, Carmona P. New accessory for studies of isotopic 1H/2H exchange and biomolecular interactions using transmission infrared spectroscopy. Anal Bioanal Chem 2006; 385:134-8. [PMID: 16572345 DOI: 10.1007/s00216-006-0381-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2005] [Revised: 02/06/2006] [Accepted: 02/17/2006] [Indexed: 10/24/2022]
Abstract
We present here a new accessory for IR transmission measurements of 1H/2H exchange, as an ancillary tool for monitoring structural features of biomolecules in aqueous solution. This new accessory results from the combination of two dialysis membranes and a conventional liquid cell having two cylinders containing 2H2O buffer. When compared with conventional transmission measurements, carried out either after dissolving lyophilized biomolecules in 2H2O or after dialyzing the aqueous solution considered against 2H2O buffer, this accessory shows the following advantages: (1) controlled measurements over the initial steps of this isotopic exchange and absence of molecular aggregation, and (2) smaller sample amounts. This new Fourier transform IR cell can also be used to analyze ligand-biomolecule and drug-cell interactions.
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52
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Encinar JA, Molina ML, Poveda JA, Barrera FN, Renart ML, Fernández AM, González-Ros JM. The influence of a membrane environment on the structure and stability of a prokaryotic potassium channel, KcsA. FEBS Lett 2005; 579:5199-204. [PMID: 16150445 DOI: 10.1016/j.febslet.2005.08.038] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2005] [Revised: 08/22/2005] [Accepted: 08/22/2005] [Indexed: 11/22/2022]
Abstract
The lack of a membrane environment in membrane protein crystals is considered one of the major limiting factors to fully imply X-ray structural data to explain functional properties of ion channels [Gulbis, J.M. and Doyle, D. (2004) Curr. Opin. Struct. Biol. 14, 440-446]. Here, we provide infrared spectroscopic evidence that the structure and stability of the potassium channel KcsA and its chymotryptic derivative 1-125 KcsA reconstituted into native-like membranes differ from those exhibited by these proteins in detergent solution, the latter taken as an approximation of the mixed detergent-protein crystal conditions.
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Affiliation(s)
- J A Encinar
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, 03202 Alicante, Spain
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53
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Abramson J, Smirnova I, Kasho V, Verner G, Iwata S, Kaback HR. The lactose permease ofEscherichia coli: overall structure, the sugar-binding site and the alternating access model for transport. FEBS Lett 2004; 555:96-101. [PMID: 14630326 DOI: 10.1016/s0014-5793(03)01087-1] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Membrane transport proteins transduce free energy stored in electrochemical ion gradients into a concentration gradient and are a major class of membrane proteins, many of which play important roles in human health and disease. Recently, the X-ray structure of the Escherichia coli lactose permease (LacY), an intensively studied member of a large group of related membrane transport proteins, was solved at 3.5 A. LacY is composed of N- and C-terminal domains, each with six transmembrane helices, symmetrically positioned within the molecule. The structure represents the inward-facing conformation, as evidenced by a large internal hydrophilic cavity open to the cytoplasmic side. The structure with a bound lactose homolog reveals the sugar-binding site in the cavity, and a mechanism for translocation across the membrane is proposed in which the sugar-binding site has alternating accessibility to either side of the membrane.
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Affiliation(s)
- Jeff Abramson
- Department of Biological Sciences, Imperial College London, London SW7 2AZ, UK
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54
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Abramson J, Smirnova I, Kasho V, Verner G, Kaback HR, Iwata S. Structure and mechanism of the lactose permease of Escherichia coli. Science 2003; 301:610-5. [PMID: 12893935 DOI: 10.1126/science.1088196] [Citation(s) in RCA: 1192] [Impact Index Per Article: 56.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Membrane transport proteins that transduce free energy stored in electrochemical ion gradients into a concentration gradient are a major class of membrane proteins. We report the crystal structure at 3.5 angstroms of the Escherichia coli lactose permease, an intensively studied member of the major facilitator superfamily of transporters. The molecule is composed of N- and C-terminal domains, each with six transmembrane helices, symmetrically positioned within the permease. A large internal hydrophilic cavity open to the cytoplasmic side represents the inward-facing conformation of the transporter. The structure with a bound lactose homolog, beta-D-galactopyranosyl-1-thio-beta-D-galactopyranoside, reveals the sugar-binding site in the cavity, and residues that play major roles in substrate recognition and proton translocation are identified. We propose a possible mechanism for lactose/proton symport (co-transport) consistent with both the structure and a large body of experimental data.
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Affiliation(s)
- Jeff Abramson
- Department of Biological Sciences, Imperial College London, London SW7 2AZ, UK
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55
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Demmers JAA, van Dalen A, de Kruijff B, Heck AJR, Killian JA. Interaction of the K+ channel KcsA with membrane phospholipids as studied by ESI mass spectrometry. FEBS Lett 2003; 541:28-32. [PMID: 12706814 DOI: 10.1016/s0014-5793(03)00282-5] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this study we have used electrospray ionization mass spectrometry (ESI-MS) to investigate interactions between the bacterial K(+) channel KcsA and membrane phospholipids. KcsA was reconstituted into lipid vesicles of variable lipid composition. These vesicles were directly analyzed by ESI-MS or mixed with trifluoroethanol (TFE) before analysis. In the resulting mass spectra, non-covalent complexes of KcsA and phospholipids were observed with an interesting lipid specificity. The anionic phosphatidylglycerol (PG), and, to a lesser extent, the zwitterionic phosphatidylethanolamine (PE), which both are abundant bacterial lipids, were found to preferentially associate with KcsA as compared to the zwitterionic phosphatidylcholine (PC). These preferred interactions may reflect the differences in affinity of these phospholipids for KcsA in the membrane.
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Affiliation(s)
- Jeroen A A Demmers
- Department of Biochemistry of Membranes, Center for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, The Netherlands.
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56
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Kelly BL, Gross A. Potassium channel gating observed with site-directed mass tagging. Nat Struct Mol Biol 2003; 10:280-4. [PMID: 12640442 DOI: 10.1038/nsb908] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2002] [Accepted: 01/27/2003] [Indexed: 11/08/2022]
Abstract
Potassium channels allow the selective flow of K+ ions across otherwise impermeable membranes. During a process called gating, these channels undergo a conformational change that proceeds from a closed to an open state. The closed state of KcsA, a prokaryotic potassium channel, has been structurally well characterized with equilibrium structural techniques. However, attempts to obtain a structural description of the gating transition of the channel have been hampered because the open state is only transiently occupied and, therefore, not readily accessible to such techniques. Here we describe a non-equilibrium technique that we call site-directed mass tagging and use this technique to probe the conformational change that KcsA undergoes during gating. The results indicate that KcsA is a dynamically modular molecule; the extracellular half of the membrane-spanning region is held rigid during gating, while the intracellular half undergoes a significant conformational change.
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Affiliation(s)
- Brent L Kelly
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University School of Medicine, 303 East Chicago Avenue, Chicago, Illinois 60611, USA
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57
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Zhang EY, Knipp GT, Ekins S, Swaan PW. Structural biology and function of solute transporters: implications for identifying and designing substrates. Drug Metab Rev 2002; 34:709-50. [PMID: 12487148 DOI: 10.1081/dmr-120015692] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Solute carrier (SLC) proteins have critical physiological roles in nutrient transport and may be utilized as a mechanism to increase drug absorption. However, we have little understanding of these proteins at the molecular level due to the absence of high-resolution crystal structures. Numerous efforts have been made in characterizing the peptide transporter (PepT1) and the apical sodium dependent bile acid transporter (ASBT) that are important for both their native transporter function as well as targets to increase absorption and act as therapeutic targets. In vitro and computational approaches have been applied to gain some insight into these transporters with some success. This represents an opportunity for optimizing molecules as substrates for the solute transporters and providing a further screening system for drug discovery. Clearly the future growth in knowledge of SLC function will be led by integrated in vitro and in silico approaches.
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Affiliation(s)
- Eric Y Zhang
- Division of Pharmaceutics, The Ohio State University, 500 West 12th Avenue, Columbus, OH 43210-1291, USA
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58
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Sorgen PL, Hu Y, Guan L, Kaback HR, Girvin ME. An approach to membrane protein structure without crystals. Proc Natl Acad Sci U S A 2002; 99:14037-40. [PMID: 12391320 PMCID: PMC137832 DOI: 10.1073/pnas.182552199] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/11/2002] [Indexed: 11/18/2022] Open
Abstract
The lactose permease of Escherichia coli catalyzes coupled translocation of galactosides and H(+) across the cell membrane. It is the best-characterized member of the Major Facilitator Superfamily, a related group of membrane proteins with 12 transmembrane domains that mediate transport of various substrates across cell membranes. Despite decades of effort and their functional importance in all kingdoms of life, no high-resolution structures have been solved for any member of this family. However, extensive biochemical, genetic, and biophysical studies on lactose permease have established its transmembrane topology, secondary structure, and numerous interhelical contacts. Here we demonstrate that this information is sufficient to calculate a structural model at the level of helix packing or better.
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Affiliation(s)
- Paul L Sorgen
- Biochemistry Department, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
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59
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Vigano C, Grimard V, Margolles A, Goormaghtigh E, van Veen HW, Konings WN, Ruysschaert JM. A new experimental approach to detect long-range conformational changes transmitted between the membrane and cytosolic domains of LmrA, a bacterial multidrug transporter. FEBS Lett 2002; 530:197-203. [PMID: 12387892 DOI: 10.1016/s0014-5793(02)03485-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
LmrA confers multidrug resistance to Lactococcus lactis by mediating the extrusion of antibiotics, out of the bacterial membrane, using the energy derived from ATP hydrolysis. Cooperation between the cytosolic and membrane-embedded domains plays a crucial role in regulating the transport ATPase cycle of this protein. In order to demonstrate the existence of a structural coupling required for the cross-talk between drug transport and ATP hydrolysis, we studied specifically the dynamic changes occurring in the membrane-embedded and cytosolic domains of LmrA by combining infrared linear dichroic spectrum measurements in the course of H/D exchange with Trp fluorescence quenching by a water-soluble attenuator. This new experimental approach, which is of general interest in the study of membrane proteins, detects long-range conformational changes, transmitted between the membrane-embedded and cytosolic regions of LmrA. On the one hand, nucleotide binding and hydrolysis in the cytosolic nucleotide binding domain cause a repacking of the transmembrane helices. On the other hand, drug binding to the transmembrane helices affects both the structure of the cytosolic regions and the ATPase activity of the nucleotide binding domain.
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Affiliation(s)
- Catherine Vigano
- Service de Structure et Fonction des Membranes Biologiques (SFMB), Université Libre de Bruxelles, P.O. Box 206/2, Bd du Triomphe, B1050 Brussels, Belgium.
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60
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Engel CK, Chen L, Privé GG. Stability of the lactose permease in detergent solutions. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1564:47-56. [PMID: 12100995 DOI: 10.1016/s0005-2736(02)00397-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Protein stability, as measured by irreversible protein aggregation, is one of the central difficulties in the handling of detergent-solubilized membrane proteins. We present a quantitative analysis of the stability of the Escherichia coli lactose (lac) permease and a series of lac permease fusion proteins containing an insertion of cytochrome(b562), T4 lysozyme or beta-lactamase in the central hydrophilic loop of the permease. The stability of the proteins was evaluated under a variety of storage conditions by both a qualitative SDS-PAGE assay and by a quantitative hplc assay. Long-chain maltoside detergents were more effective at maintaining purified protein in solution than detergents with smaller head groups and/or shorter alkyl tails. A full factorial experiment established that the proteins were insensitive to sodium chloride concentrations, but greatly stabilized by glycerol, low temperature and the combination of glycerol and low temperature. The accurate quantitation of the protein by absorbance spectroscopy required exclusion of all contact with clarified polypropylene or polyvinyl chloride (PVC) materials. Although some of the fusion proteins were more prone to aggregation than the wild-type permease, the stability of a fusion protein containing a cytochrome(b562) insertion was indistinguishable from that of native lac permease.
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Affiliation(s)
- Christian K Engel
- Division of Molecular and Structural Biology, Ontario Cancer Institute, Toronto, Canada
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61
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Abstract
Transport proteins have critical physiological roles in nutrient transport and may be utilized as a mechanism to increase drug absorption. However, we have little understanding of these proteins at the molecular level due to the absence of high-resolution crystal structures. Numerous efforts have been made to characterize the P-glycoprotein efflux pump, the peptide transporter (PepT1) and the apical sodium-dependent transporter (ASBT) which are important not only for their native transporter function but also as drug targets to increase absorption and bioactivity. In vitro and computational approaches have been applied to gain some insight into these transporters with some success. This represents an opportunity for optimizing molecules as substrates for the solute transporters and providing a further screening system for drug discovery. Clearly the future growth in knowledge of transporter function will be led by integrated in vitro and in silico approaches.
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Affiliation(s)
- Eric Y Zhang
- Division of Pharmaceutics, The Ohio State University, 500 West 12th Avenue, Columbus, OH 43210-1291, USA
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62
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Kaback HR, Sahin-Tóth M, Weinglass AB. The kamikaze approach to membrane transport. Nat Rev Mol Cell Biol 2001; 2:610-20. [PMID: 11483994 DOI: 10.1038/35085077] [Citation(s) in RCA: 253] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Membrane transport proteins catalyse the movement of molecules into and out of cells and organelles, but their hydrophobic and metastable nature often makes them difficult to study by traditional means. Novel approaches that have been developed and applied to one membrane transport protein, the lactose permease from Escherichia coli, are now being used to study various other membrane proteins.
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Affiliation(s)
- H R Kaback
- Howard Hughes Medical Institute, Department of Physiology, University of California, Los Angeles, California 90095-1662, USA.
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63
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Abstract
Escherichia coli lactose permease, a paradigm for membrane transport proteins, and Streptomyces lividans KcsA, a paradigm for K+ channels, are compared on the level of structure, dynamics, and function. The homotetrameric channel, which allows the downhill movement of K+ with an electrochemical gradient, is relatively rigid and inflexible, as observed by Fourier transform infrared spectroscopy. Lactose permease catalyzes transduction of free energy stored in an electrochemical H+ gradient into work in the form of a concentration gradient. In marked contrast to KcsA, the permease exhibits a high degree of H/D exchange, in addition to enhanced sensitivity to lateral lipid packing pressure, thereby indicating that this symport protein is extremely flexible and conformationally active. Finally, the differences between lactose permease and KcsA are discussed in the context of their specific functions with particular emphasis on differences between coupling in symport proteins and gating in channels.
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Affiliation(s)
- J le Coutre
- Howard Hughes Medical Institute, Department of Physiology, University of California, Los Angeles, CA 90095-1662, USA
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64
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Dave N, Troullier A, Mus-Veteau I, Duñach M, Leblanc G, Padrós E. Secondary structure components and properties of the melibiose permease from Escherichia coli: a fourier transform infrared spectroscopy analysis. Biophys J 2000; 79:747-55. [PMID: 10920008 PMCID: PMC1300974 DOI: 10.1016/s0006-3495(00)76332-6] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The structure of the melibiose permease from Escherichia coli has been investigated by Fourier transform infrared spectroscopy, using the purified transporter either in the solubilized state or reconstituted in E. coli lipids. In both instances, the spectra suggest that the permease secondary structure is dominated by alpha-helical components (up to 50%) and contains beta-structure (20%) and additional components assigned to turns, 3(10) helix, and nonordered structures (30%). Two distinct and strong absorption bands are recorded at 1660 and 1653 cm(-1), i.e., in the usual range of absorption of helices of membrane proteins. Moreover, conditions that preserve the transporter functionality (reconstitution in liposomes or solubilization with dodecyl maltoside) make possible the detection of two separate alpha-helical bands of comparable intensity. In contrast, a single intense band, centered at approximately 1656 cm(-1), is recorded from the inactive permease in Triton X-100, or a merged and broader signal is recorded after the solubilized protein is heated in dodecyl maltoside. It is suggested that in the functional permease, distinct signals at 1660 and 1653 cm(-1) arise from two different populations of alpha-helical domains. Furthermore, the sodium- and/or melibiose-induced changes in amide I line shape, and in particular, in the relative amplitudes of the 1660 and 1653 cm(-1) bands, indicate that the secondary structure is modified during the early step of sugar transport. Finally, the observation that approximately 80% of the backbone amide protons can be exchanged suggests high conformational flexibility and/or a large accessibility of the membrane domains to the aqueous solvent.
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Affiliation(s)
- N Dave
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, Bellaterra, Barcelona 08193, Spain
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65
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Whitelegge JP, le Coutre J, Lee JC, Engel CK, Privé GG, Faull KF, Kaback HR. Toward the bilayer proteome, electrospray ionization-mass spectrometry of large, intact transmembrane proteins. Proc Natl Acad Sci U S A 1999; 96:10695-8. [PMID: 10485888 PMCID: PMC17945 DOI: 10.1073/pnas.96.19.10695] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Genes encoding membrane proteins comprise a substantial proportion of genomes sequenced to date, but ability to perform structural studies on this portion of the proteome is limited. Electrospray ionization-MS (ESI-MS) of an intact protein generates a profile defining the native covalent state of the gene product and its heterogeneity. Here we apply ESI-MS technology with accuracy exceeding 0.01% to a hydrophobic membrane protein with 12-transmembrane alpha-helices, the full-length lactose permease from Escherichia coli. Furthermore, ESI-MS is used to titrate reactive thiols with N-ethylmaleimide. Treatment of the native protein solubilized in detergent micelles reveals only two reactive thiols, and both are protected by a substrate analog.
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Affiliation(s)
- J P Whitelegge
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
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66
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Borgnia MJ, Kozono D, Calamita G, Maloney PC, Agre P. Functional reconstitution and characterization of AqpZ, the E. coli water channel protein. J Mol Biol 1999; 291:1169-79. [PMID: 10518952 DOI: 10.1006/jmbi.1999.3032] [Citation(s) in RCA: 209] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Understanding the selectivity of aquaporin water channels will require structural and functional studies of wild-type and modified proteins; however, expression systems have not previously yielded aquaporins in the necessary milligram quantities. Here we report expression of a histidine-tagged form of Escherichia coli aquaporin-Z (AqpZ) in its homologous expression system. 10-His-AqpZ is solubilized and purified to near homogeneity in a single step with a final yield of approximately 2.5 mg/l of culture. The histidine tag is removed by trypsin, yielding the native protein with the addition of three N-terminal residues, as confirmed by microsequencing. Sucrose gradient sedimentation analysis showed that the native, solubilized AqpZ protein is a trypsin-resistant tetramer. Unlike other known aquaporins, AqpZ tetramers are not readily dissociated by 1% SDS at neutral pH. Hydrophilic reducing agents have a limited effect on the stability of the tetramer in 1% SDS, whereas incubations for more than 24 hours, pH values below 5.6, or exposure to the hydrophobic reducing agent ethanedithiol cause dissociation into monomers. Cys20, but not Cys9, is necessary for the stability of the AqpZ tetramer in SDS. Upon reconstitution into proteoliposomes, AqpZ displays very high osmotic water permeability (pf > or = 10 x 10(-14) cm3 s-1 subunit-1) and low Arrhenius activation energy (Ea = 3.7 kcal/mol), similar to mammalian aquaporin-1 (AQP1). No permeation by glycerol, urea or sorbitol was detected. Expression of native and modified AqpZ in milligram quantities has permitted biophysical characterization of this remarkably stable aquaporin tetramer, which is being utilized for high-resolution structural studies.
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Affiliation(s)
- M J Borgnia
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205-2185, USA
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67
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Larive CK, Lunte SM, Zhong M, Perkins MD, Wilson GS, Gokulrangan G, Williams T, Afroz F, Schöneich C, Derrick TS, Middaugh CR, Bogdanowich-Knipp S. Separation and analysis of peptides and proteins. Anal Chem 1999; 71:389R-423R. [PMID: 10409086 DOI: 10.1021/a1990013o] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- C K Larive
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045
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68
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Kaback HR, Wu J. What To Do while Awaiting Crystals of a Membrane Transport Protein and Thereafter. Acc Chem Res 1999. [DOI: 10.1021/ar970256i] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- H. Ronald Kaback
- Howard Hughes Medical Institute, Departments of Physiology and Microbiology & Molecular Genetics, Molecular Biology Institute, University of CaliforniaLos Angeles, Los Angeles, California 90095-1662
| | - Jianhua Wu
- Howard Hughes Medical Institute, Departments of Physiology and Microbiology & Molecular Genetics, Molecular Biology Institute, University of CaliforniaLos Angeles, Los Angeles, California 90095-1662
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69
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Frillingos S, Sahin-Tóth M, Wu J, Kaback HR. Cys-scanning mutagenesis: a novel approach to structure function relationships in polytopic membrane proteins. FASEB J 1998; 12:1281-99. [PMID: 9761772 DOI: 10.1096/fasebj.12.13.1281] [Citation(s) in RCA: 311] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The entire lactose permease of Escherichia coli, a polytopic membrane transport protein that catalyzes beta-galactoside/H+ symport, has been subjected to Cys-scanning mutagenesis in order to determine which residues play an obligatory role in the mechanism and to create a library of mutants with a single-Cys residue at each position of the molecule for structure/function studies. Analysis of the mutants has led to the following: 1) only six amino acid side chains play an irreplaceable role in the transport mechanism; 2) positions where the reactivity of the Cys replacement is increased upon ligand binding are identified; 3) positions where the reactivity of the Cys replacement is decreased by ligand binding are identified; 4) helix packing, helix tilt, and ligand-induced conformational changes are determined by using the library of mutants in conjunction with a battery of site-directed techniques; 5) the permease is a highly flexible molecule; and 6) a working model that explains coupling between beta-galactoside and H+ translocation. structure-function relationships in polytopic membrane proteins.
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Affiliation(s)
- S Frillingos
- Howard Hughes Medical Institute, Departments of Physiology and Microbiology and Molecular Genetics, Molecular Biology Institute, University of California Los Angeles, Los Angeles, California 90024
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70
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Heginbotham L, Kolmakova-Partensky L, Miller C. Functional reconstitution of a prokaryotic K+ channel. J Gen Physiol 1998; 111:741-9. [PMID: 9607934 PMCID: PMC2217152 DOI: 10.1085/jgp.111.6.741] [Citation(s) in RCA: 169] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/1998] [Accepted: 04/03/1998] [Indexed: 11/20/2022] Open
Abstract
SliK, a K+ channel encoded by the Streptomyces KcsA gene, was expressed, purified, and reconstituted in liposomes. A concentrative 86Rb+ flux assay was used to assess the ion transport properties of SliK. SliK-mediated ionic flux shows strong selectivity for K+ over Na+ and is inhibited by micromolar concentrations of Ba2+, mirroring the basic permeation characteristic of eukaryotic K+ channels studied by electrophysiological methods. 86Rb+ uptake kinetics and equilibrium measurements also demonstrate that the purified protein is fully active.
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Affiliation(s)
- L Heginbotham
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, Massachusetts 02254, USA
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