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Xu L, Weatherbee-Martin N, Liu XQ, Rainey JK. Recombinant Silk Fiber Properties Correlate to Prefibrillar Self-Assembly. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2019; 15:e1805294. [PMID: 30756524 DOI: 10.1002/smll.201805294] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2018] [Revised: 01/18/2019] [Indexed: 06/09/2023]
Abstract
Spider silks are desirable materials with mechanical properties superior to most synthetic materials coupled with biodegradability and biocompatibility. In order to replicate natural silk properties using recombinant spider silk proteins (spidroins) and wet-spinning methods, the focus to date has typically been on modifying protein sequence, protein size, and spinning conditions. Here, an alternative approach is demonstrated. Namely, using the same ≈57 kDa recombinant aciniform silk protein with a consistent wet-spinning protocol, fiber mechanical properties are shown to significantly differ as a function of the solvent used to dissolve the protein at high concentration (the "spinning dope" solution). A fluorinated acid/alcohol/water dope leads to drastic improvement in fibrillar extensibility and, correspondingly, toughness compared to fibers produced using a previously developed fluorinated alcohol/water dope. To understand the underlying cause for these mechanical differences, morphology and structure of the two classes of silk fiber are compared, with features tracing back to dope-state protein structuring and preassembly. Specifically, distinct classes of spidroin nanoparticles appear to form in each dope prior to fiber spinning and these preassembled states are, in turn, linked to fiber morphology, structure, and mechanical properties. Tailoring of dope-state spidroin nanoparticle assembly, thus, appears a promising strategy to modulate fibrillar silk properties.
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Affiliation(s)
- Lingling Xu
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
| | - Nathan Weatherbee-Martin
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
| | - Xiang-Qin Liu
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
| | - Jan K Rainey
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
- Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
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Langelaan DN, Pandey A, Sarker M, Rainey JK. Preserved Transmembrane Segment Topology, Structure, and Dynamics in Disparate Micellar Environments. J Phys Chem Lett 2017; 8:2381-2386. [PMID: 28492329 PMCID: PMC5770213 DOI: 10.1021/acs.jpclett.7b00867] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Detergent micelles are frequently employed as membrane mimetics for solution-state membrane protein nuclear magnetic resonance spectroscopy. Here we compare topology, structure, ps-ns time-scale dynamics, and hydrodynamics of a model protein with one transmembrane (TM) segment (residues 1-55 of the apelin receptor, APJ, a G-protein-coupled receptor) in three distinct, commonly used micellar environments. In each environment, two solvent-protected helical segments connected by a solvent-exposed kink were observed. The break in helical character at the kink was maintained in a helix-stabilizing fluorinated alcohol environment, implying that this structural feature is inherent. Molecular dynamics simulations also substantiate favorable self-assembly of compact protein-micelle complexes with a more dynamic, solvent-exposed kink. Despite the observed similarity in TM segment behavior, micelle-dependent differences were clear in the structure, dynamics, and compactness of the 30-residue, extramembrane N-terminal tail of the protein. This would affect intermolecular interactions and, correspondingly, the functional state of the membrane protein.
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Affiliation(s)
- David N. Langelaan
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax NS B3H 4R2, Canada
| | - Aditya Pandey
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax NS B3H 4R2, Canada
| | - Muzaddid Sarker
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax NS B3H 4R2, Canada
| | - Jan K. Rainey
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax NS B3H 4R2, Canada
- Department of Chemistry, Dalhousie University, Halifax NS B3H 4R2, Canada
- Corresponding author:
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Counillon L, Bouret Y, Marchiq I, Pouysségur J. Na(+)/H(+) antiporter (NHE1) and lactate/H(+) symporters (MCTs) in pH homeostasis and cancer metabolism. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2016; 1863:2465-80. [PMID: 26944480 DOI: 10.1016/j.bbamcr.2016.02.018] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Revised: 02/19/2016] [Accepted: 02/22/2016] [Indexed: 12/17/2022]
Abstract
The Na(+)/H(+)-exchanger NHE1 and the monocarboxylate transporters MCT1 and MCT4 are crucial for intracellular pH regulation, particularly under active metabolism. NHE1, a reversible antiporter, uses the energy provided by the Na(+) gradient to expel H(+) ions generated in the cytosol. The reversible H(+)/lactate(-) symporters MCT1 and 4 cotransport lactate and proton, leading to the net extrusion of lactic acid in glycolytic tumors. In the first two sections of this article we review important features and remaining questions on the structure, biochemical function and cellular roles of these transporters. We then use a fully-coupled mathematical model to simulate their relative contribution to pH regulation in response to lactate production, as it occurs in highly hypoxic and glycolytic tumor cells. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.
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Affiliation(s)
- Laurent Counillon
- University of Nice-Sophia Antipolis, LP2M UMR7370, Faculty of Medicine, 28 Avenue Valombrose, 06107 Nice France; Laboratories of Excellence Ion Channel Science and Therapeutics, France.
| | - Yann Bouret
- University of Nice-Sophia Antipolis, LPMC UMR 7336, 28 Avenue Valrose, 06108 Nice, France
| | - Ibtissam Marchiq
- IRCAN, Centre A. Lacassagne, University of Nice-Sophia Antipolis, 33 Avenue Valombrose, 06107 Nice, France
| | - Jacques Pouysségur
- IRCAN, Centre A. Lacassagne, University of Nice-Sophia Antipolis, 33 Avenue Valombrose, 06107 Nice, France; Centre Scientifique de Monaco (CSM), 8, Quai Antoine 1er, Monaco.
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Alves C, Lee BL, Sykes BD, Fliegel L. Structural and Functional Analysis of the Transmembrane Segment Pair VI and VII of the NHE1 Isoform of the Na+/H+ Exchanger. Biochemistry 2014; 53:3658-70. [DOI: 10.1021/bi500392y] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Claudia Alves
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Brian L. Lee
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Brian D. Sykes
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Larry Fliegel
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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Langelaan DN, Reddy T, Banks AW, Dellaire G, Dupré DJ, Rainey JK. Structural features of the apelin receptor N-terminal tail and first transmembrane segment implicated in ligand binding and receptor trafficking. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:1471-83. [PMID: 23438363 DOI: 10.1016/j.bbamem.2013.02.005] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Revised: 01/17/2013] [Accepted: 02/13/2013] [Indexed: 12/20/2022]
Abstract
G-protein coupled receptors (GPCRs) comprise a large family of membrane proteins with rich functional diversity. Signaling through the apelin receptor (AR or APJ) influences the cardiovascular system, central nervous system and glucose regulation. Pathophysiological involvement of apelin has been shown in atherosclerosis, cancer, human immunodeficiency virus-1 (HIV-1) infection and obesity. Here, we present the high-resolution nuclear magnetic resonance (NMR) spectroscopy-based structure of the N-terminus and first transmembrane (TM) segment of AR (residues 1-55, AR55) in dodecylphosphocholine micelles. AR55 consists of two disrupted helices, spanning residues D14-K25 and A29-R55(1.59). Molecular dynamics (MD) simulations of AR built from a hybrid of experimental NMR and homology model-based restraints allowed validation of the AR55 structure in the context of the full-length receptor in a hydrated bilayer. AR55 structural features were functionally probed using mutagenesis in full-length AR through monitoring of apelin-induced extracellular signal-regulated kinase (ERK) phosphorylation in transiently transfected human embryonic kidney (HEK) 293A cells. Residues E20 and D23 form an extracellular anionic face and interact with lipid headgroups during MD simulations in the absence of ligand, producing an ideal binding site for a cationic apelin ligand proximal to the membrane-water interface, lending credence to membrane-catalyzed apelin-AR binding. In the TM region of AR55, N46(1.50) is central to a disruption in helical character. G42(1.46), G45(1.49) and N46(1.50), which are all involved in the TM helical disruption, are essential for proper trafficking of AR. In summary, we introduce a new correlative NMR spectroscopy and computational biochemistry methodology and demonstrate its utility in providing some of the first high-resolution structural information for a peptide-activated GPCR TM domain.
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Affiliation(s)
- David N Langelaan
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
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Gayen S, Kang C. Solution structure of a human minimembrane protein Ost4, a subunit of the oligosaccharyltransferase complex. Biochem Biophys Res Commun 2011; 409:572-6. [DOI: 10.1016/j.bbrc.2011.05.050] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Accepted: 05/10/2011] [Indexed: 11/28/2022]
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Lee BL, Sykes BD, Fliegel L. Structural analysis of the Na+/H+ exchanger isoform 1 (NHE1) using the divide and conquer approachThis paper is one of a selection of papers published in a Special Issue entitled CSBMCB 53rd Annual Meeting — Membrane Proteins in Health and Disease, and has undergone the Journal’s usual peer review process. Biochem Cell Biol 2011; 89:189-99. [DOI: 10.1139/o10-140] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The sodium/proton exchanger isoform 1 (NHE1) is an ubiquitous plasma membrane protein that regulates intracellular pH by removing excess intracellular acid. NHE1 is important in heart disease and cancer, making it an attractive therapeutic target. Although much is known about the function of NHE1, current structural knowledge of NHE1 is limited to two conflicting topology models: a low-resolution molecular envelope from electron microscopy, and comparison with a crystal structure of a bacterial homologue, NhaA. Our laboratory has used high-resolution nuclear magnetic resonance (NMR) spectroscopy to investigate the structures of individual transmembrane helices of NHE1 — a divide and conquer approach to the study of this membrane protein. In this review, we discuss the structural and functional insights obtained from this approach in combination with functional data obtained from mutagenesis experiments on the protein. We also compare the known structure of NHE1 transmembrane segments with the structural and functional insights obtained from a bacterial sodium/proton exchanger homologue, NhaA. The structures of regions of the NHE1 protein that have been determined have both similarities and specific differences to the crystal structure of the NhaA protein. These have allowed insights into both the topology and the function of the NHE1 protein.
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Affiliation(s)
- Brian L. Lee
- Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Brian D. Sykes
- Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Larry Fliegel
- Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
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Tzeng J, Lee BL, Sykes BD, Fliegel L. Structural and functional analysis of transmembrane segment VI of the NHE1 isoform of the Na+/H+ exchanger. J Biol Chem 2010; 285:36656-65. [PMID: 20843797 PMCID: PMC2978594 DOI: 10.1074/jbc.m110.161471] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2010] [Revised: 08/23/2010] [Indexed: 01/17/2023] Open
Abstract
The Na(+)/H(+) exchanger isoform 1 is a ubiquitously expressed integral membrane protein. It resides on the plasma membrane of cells and regulates intracellular pH in mammals by extruding an intracellular H(+) in exchange for one extracellular Na(+). We characterized structural and functional aspects of the transmembrane segment (TM) VI (residues 227-249) by using cysteine scanning mutagenesis and high resolution NMR. Each residue of TM VI was mutated to cysteine in the background of the cysteineless NHE1 protein, and the sensitivity to water-soluble sulfhydryl-reactive compounds (2-(trimethylammonium)ethyl)methanethiosulfonate (MTSET) and (2-sulfonatoethyl)methanethiosulfonate (MTSES) was determined for those residues with significant activity remaining. Three residues were essentially inactive when mutated to Cys: Asp(238), Pro(239), and Glu(247). Of the remaining residues, proteins with the mutations N227C, I233C, and L243C were strongly inhibited by MTSET, whereas amino acids Phe(230), Gly(231), Ala(236), Val(237), Ala(244), Val(245), and Glu(248) were partially inhibited by MTSET. MTSES did not affect the activity of the mutant NHE1 proteins. The structure of a peptide representing TM VI was determined using high resolution NMR spectroscopy in dodecylphosphocholine micelles. TM VI contains two helical regions oriented at an approximate right angle to each other (residues 229-236 and 239-250) surrounding a central unwound region. This structure bears a resemblance to TM IV of the Escherichia coli protein NhaA. The results demonstrate that TM VI of NHE1 is a discontinuous pore-lining helix with residues Asn(227), Ile(233), and Leu(243) lining the translocation pore.
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Affiliation(s)
- Jennifer Tzeng
- From the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Brian L. Lee
- From the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Brian D. Sykes
- From the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Larry Fliegel
- From the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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Tremblay ML, Banks AW, Rainey JK. The predictive accuracy of secondary chemical shifts is more affected by protein secondary structure than solvent environment. JOURNAL OF BIOMOLECULAR NMR 2010; 46:257-270. [PMID: 20213252 DOI: 10.1007/s10858-010-9400-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2009] [Accepted: 02/17/2010] [Indexed: 05/28/2023]
Abstract
Biomolecular NMR spectroscopy frequently employs estimates of protein secondary structure using secondary chemical shift (Deltadelta) values, measured as the difference between experimental and random coil chemical shifts (RCCS). Most published random coil data have been determined in aqueous conditions, reasonable for non-membrane proteins, but potentially less relevant for membrane proteins. Two new RCCS sets are presented here, determined in dimethyl sulfoxide (DMSO) and chloroform:methanol:water (4:4:1 by volume) at 298 K. A web-based program, CS-CHEMeleon, has been implemented to determine the accuracy of secondary structure assessment by calculating and comparing Deltadelta values for various RCCS datasets. Using CS-CHEMeleon, Deltadelta predicted versus experimentally determined secondary structures were compared for large datasets of membrane and non-membrane proteins as a function of RCCS dataset, Deltadelta threshold, nucleus, localized parameter averaging and secondary structure type. Optimized Deltadelta thresholds are presented both for published and for the DMSO and chloroform:methanol:water derived RCCS tables. Despite obvious RCCS variations between datasets, prediction of secondary structure was consistently similar. Strikingly, predictive accuracy seems to be most dependent upon the type of secondary structure, with helices being the most accurately predicted by Deltadelta values using five different RCCS tables. We suggest caution when using Deltadelta-based restraints in structure calculations as the underlying dataset may be biased. Comparative assessment of multiple RCCS datasets should be performed, and resulting Deltadelta-based restraints weighted appropriately relative to other experimental restraints.
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Affiliation(s)
- Marie-Laurence Tremblay
- Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, NS, B3H 1X5, Canada
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Reddy T, Li X, Fliegel L, Sykes BD, Rainey JK. Correlating structure, dynamics, and function in transmembrane segment VII of the Na+/H+ exchanger isoform 1. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:94-104. [DOI: 10.1016/j.bbamem.2009.06.025] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Revised: 06/17/2009] [Accepted: 06/29/2009] [Indexed: 10/20/2022]
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Bay DC, Budiman RA, Nieh MP, Turner RJ. Multimeric forms of the small multidrug resistance protein EmrE in anionic detergent. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1798:526-35. [PMID: 20036636 DOI: 10.1016/j.bbamem.2009.12.017] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Revised: 12/18/2009] [Accepted: 12/21/2009] [Indexed: 11/16/2022]
Abstract
Escherichia coli multidrug resistance protein E (EmrE) is a four transmembrane alpha-helix protein, and a member of the small multidrug resistance protein family that confers resistance to a broad range of quaternary cation compounds (QCC) via proton motive force. The multimeric states of EmrE protein during transport or ligand binding are variable and specific to the conditions of study. To explore EmrE multimerization further, EmrE extracted from E. coli membranes was solubilized in anionic detergent, sodium dodecyl sulphate (SDS), at varying protein concentrations. At low concentrations (</=1muM) in SDS-EmrE is monomeric, but upon increasing EmrE concentration, a variety of multimeric states can be observed by SDS-Tricine polyacrylamide gel electrophoresis (PAGE). Addition of the (QCC), tetraphenyl phosphonium (TPP), to SDS-EmrE samples enhanced EmrE multimer formation using SDS-Tricine PAGE. The relative shapes of EmrE multimers in SDS with or without TPP addition were determined by small angle neutron scattering (SANS) analysis and revealed that EmrE dimers altered in conformation depending on the SDS concentration. SANS analysis also revealed that relative shapes of larger EmrE multimers (>/=100nm sizes) altered in the presence of TPP. Circular dichroism spectropolarimetry displayed no differences in secondary structure under the conditions studied. Fluorescence spectroscopy of SDS-EmrE protein demonstrated that aromatic residues, Trp and Tyr, are more susceptible to SDS concentration than TPP addition, but both residues exhibit enhanced quenching at high ligand concentrations. Hence, EmrE forms various multimers in SDS that are influenced by detergent concentration and TPP substrate addition.
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Affiliation(s)
- Denice C Bay
- Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada
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Langelaan DN, Rainey JK. Headgroup-dependent membrane catalysis of apelin-receptor interactions is likely. J Phys Chem B 2009; 113:10465-71. [PMID: 19708686 PMCID: PMC2736645 DOI: 10.1021/jp904562q] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2009] [Revised: 06/11/2009] [Indexed: 12/18/2022]
Abstract
Apelin is the peptidic ligand for the G-protein-coupled receptor APJ. The apelin-APJ system is important in cardiovascular regulation, fluid homeostasis, and angiogenesis, among other roles. In this study, we investigate interactions between apelin and membrane-mimetic micelles of the detergents sodium dodecyl sulfate (SDS), dodecylphosphocholine (DPC), and 1-palmitoyl-2-hydroxy-sn-glycero-3-[phospho-rac-(1-glycerol)] (LPPG). Far-ultraviolet circular dichroism spectropolarimetry and diffusion-ordered spectroscopy indicate that apelin peptides bind to micelles of the anionic detergents SDS and LPPG much more favorably than to zwitterionic DPC micelles. Nuclear magnetic resonance spectroscopy allowed full characterization of the interactions of apelin-17 with SDS micelles. Titration with paramagnetic agents and structural determination of apelin-17 in SDS indicate that R6-K12 is highly structured, with R6-L9 directly interacting with headgroups of the micelle. Type I beta-turns are initiated between R6 and L9, and a well-defined type IV beta-turn is initiated at S10. Furthermore, binding of apelin-17 to SDS micelles causes structuring of M15-F17, with no evidence for direct binding of this region to the micelles. These results are placed into the context of the membrane catalysis hypothesis for peptide-receptor binding, and a hypothetical mechanism of APJ binding and activation by apelin is advanced.
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Affiliation(s)
| | - Jan K. Rainey
- To whom correspondence should be addressed. Phone: (902) 494-4632. Fax: (902) 494-1355. E-mail:
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Lee BL, Li X, Liu Y, Sykes BD, Fliegel L. Structural and functional analysis of transmembrane XI of the NHE1 isoform of the Na+/H+ exchanger. J Biol Chem 2009; 284:11546-56. [PMID: 19176522 DOI: 10.1074/jbc.m809201200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The Na(+)/H(+) exchanger isoform 1 is a ubiquitously expressed integral membrane protein that regulates intracellular pH in mammals by extruding an intracellular H(+) in exchange for one extracellular Na(+). We characterized structural and functional aspects of the critical transmembrane (TM) segment XI (residues 449-470) by using cysteine scanning mutagenesis and high resolution NMR. Each residue of TM XI was mutated to cysteine in the background of the cysteine-less protein and the sensitivity to water-soluble sulfhydryl reactive compounds MTSET ((2-(trimethylammonium) ethyl)methanethiosulfonate) and MTSES ((2-sulfonatoethyl) methanethiosulfonate) was determined for those residues with at least moderate activity remaining. Of the residues tested, only proteins with mutations L457C, I461C, and L465C were inhibited by MTSET. The activity of the L465C mutant was almost completely eliminated, whereas that of the L457C and I461C mutants was partially affected. The structure of a peptide representing TM XI (residues Lys(447)-Lys(472)) was determined using high resolution NMR spectroscopy in dodecylphosphocholine micelles. The structure consisted of helical regions between Asp(447)-Tyr(454) and Phe(460)-Lys(471) at the N and C termini of the peptide, respectively, connected by a region with poorly defined, irregular structure consisting of residues Gly(455)-Gly(459). TM XI of NHE1 had a structural similarity to TM XI of the Escherichia coli Na(+)/H(+) exchanger NhaA. The results suggest that TM XI is a discontinuous helix, with residue Leu(465) contributing to the pore.
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Affiliation(s)
- Brian L Lee
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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Langelaan DN, Bebbington EM, Reddy T, Rainey JK. Structural Insight into G-Protein Coupled Receptor Binding by Apelin. Biochemistry 2009; 48:537-48. [DOI: 10.1021/bi801864b] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- David N. Langelaan
- Departments of Biochemistry & Molecular Biology and Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 1X5 Canada
| | - E. Meghan Bebbington
- Departments of Biochemistry & Molecular Biology and Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 1X5 Canada
| | - Tyler Reddy
- Departments of Biochemistry & Molecular Biology and Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 1X5 Canada
| | - Jan K. Rainey
- Departments of Biochemistry & Molecular Biology and Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 1X5 Canada
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Reddy T, Ding J, Li X, Sykes BD, Rainey JK, Fliegel L. Structural and functional characterization of transmembrane segment IX of the NHE1 isoform of the Na+/H+ exchanger. J Biol Chem 2008; 283:22018-30. [PMID: 18508767 DOI: 10.1074/jbc.m803447200] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Na(+)/H(+) exchanger isoform 1 (NHE1) is an integral membrane protein that regulates intracellular pH by removing one intracellular H(+) in exchange for one extracellular Na(+). It has a large N-terminal membrane domain of 12 transmembrane segments and an intracellular C-terminal regulatory domain. We characterized the cysteine accessibility of amino acids of the putative transmembrane segment IX (residues 339-363). Each residue was mutated to cysteine in a functional cysteineless NHE1 protein. Of 25 amino acids mutated, 5 were inactive or nearly so after mutation to cysteine. Several of these showed aberrant targeting to the plasma membrane and reduced expression of the intact protein, whereas others were expressed and targeted correctly but had defective NHE1 function. Of the active mutants, Glu(346) and Ser(351) were inhibited >70% by positively charged [2-(trimethylammonium)-ethyl]methanethiosulfonate but not by anionic [2-sulfonatoethyl]methanethiosulfonate, suggesting that they are pore lining and make up part of the cation conduction pathway. Both mutants also had decreased affinity for Na(+) and decreased activation by intracellular protons. The structure of a peptide representing amino acids 338-365 was determined by using high resolution NMR in dodecylphosphocholine micelles. The structure contained two helical regions (amino acids Met(340)-Ser(344) and Ile(353)-Ser(359)) kinked with a large bend angle around a pivot point at amino acid Ser(351). The results suggest that transmembrane IX is critical with pore-lining residues and a kink at the functionally important residue Ser(351).
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Affiliation(s)
- Tyler Reddy
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada
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