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Wang LY, Ravi VM, Leblanc G, Padrós E, Cladera J, Perálvarez-Marín A. Helical unwinding and side-chain unlocking unravel the outward open conformation of the melibiose transporter. Sci Rep 2016; 6:33776. [PMID: 27658476 PMCID: PMC5034317 DOI: 10.1038/srep33776] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 08/30/2016] [Indexed: 11/09/2022] Open
Abstract
Molecular dynamics simulations have been used to study the alternate access mechanism of the melibiose transporter from Escherichia coli. Starting from the outward-facing partially occluded form, 2 out of 12 simulations produced an outward full open form and one partially open, whereas the rest yielded fully or partially occluded forms. The shape of the outward-open form resembles other outward-open conformations of secondary transporters. During the transporter opening, conformational changes in some loops are followed by changes in the periplasm region of transmembrane helix 7. Helical curvature relaxation and unlocking of hydrophobic and ionic locks promote the outward opening of the transporter making accessible the substrate binding site. In particular, FRET studies on mutants of conserved aromatic residues of extracellular loop 4 showed lack of substrate binding, emphasizing the importance of this loop for making crucial interactions that control the opening of the periplasmic side. This study indicates that the alternate access mechanism for the melibiose transporter fits better into a flexible gating mechanism rather than the archetypical helical rigid-body rocker-switch mechanism.
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Affiliation(s)
- Li-Ying Wang
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Vidhya M Ravi
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Gérard Leblanc
- Direction des Sciences du Vivant, Direction des programmes et valorization, CEA Fontenay-aux-Roses, 92265 Fontenay-aux-Roses CEDEX France
| | - Esteve Padrós
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Josep Cladera
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Alex Perálvarez-Marín
- Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
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Lin Y, Bogdanov M, Tong S, Guan Z, Zheng L. Substrate Selectivity of Lysophospholipid Transporter LplT Involved in Membrane Phospholipid Remodeling in Escherichia coli. J Biol Chem 2015; 291:2136-49. [PMID: 26613781 DOI: 10.1074/jbc.m115.700419] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Indexed: 11/06/2022] Open
Abstract
Lysophospholipid transporter (LplT) was previously found to be primarily involved in 2-acyl lysophosphatidylethanolamine (lyso-PE) recycling in Gram-negative bacteria. This work identifies the potent role of LplT in maintaining membrane stability and integrity in the Escherichia coli envelope. Here we demonstrate the involvement of LplT in the recycling of three major bacterial phospholipids using a combination of an in vitro lysophospholipid binding assay using purified protein and transport assays with E. coli spheroplasts. Our results show that lyso-PE and lysophosphatidylglycerol, but not lysophosphatidylcholine, are taken up by LplT for reacylation by acyltransferase/acyl-acyl carrier protein synthetase on the inner leaflet of the membrane. We also found a novel cardiolipin hydrolysis reaction by phospholipase A2 to form diacylated cardiolipin progressing to the completely deacylated headgroup. These two distinct cardiolipin derivatives were both translocated with comparable efficiency to generate triacylated cardiolipin by acyltransferase/acyl-acyl carrier protein synthetase, demonstrating the first evidence of cardiolipin remodeling in bacteria. These findings support that a fatty acid chain is not required for LplT transport. We found that LplT cannot transport lysophosphatidic acid, and its substrate binding was not inhibited by either orthophosphate or glycerol 3-phosphate, indicating that either a glycerol or ethanolamine headgroup is the chemical determinant for substrate recognition. Diacyl forms of PE, phosphatidylglycerol, or the tetra-acylated form of cardiolipin could not serve as a competitive inhibitor in vitro. Based on an evolutionary structural model, we propose a "sideways sliding" mechanism to explain how a conserved membrane-embedded α-helical interface excludes diacylphospholipids from the LplT binding site to facilitate efficient flipping of lysophospholipid across the cell membrane.
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Affiliation(s)
- Yibin Lin
- From the Center for Membrane Biology, Department of Biochemistry and Molecular Biology, The University of Texas Houston Medical School, Houston, Texas 77030 and
| | - Mikhail Bogdanov
- From the Center for Membrane Biology, Department of Biochemistry and Molecular Biology, The University of Texas Houston Medical School, Houston, Texas 77030 and
| | - Shuilong Tong
- From the Center for Membrane Biology, Department of Biochemistry and Molecular Biology, The University of Texas Houston Medical School, Houston, Texas 77030 and
| | - Ziqiang Guan
- Department of Biochemistry, Duke University Medical School, Durham, North Carolina 27703
| | - Lei Zheng
- From the Center for Membrane Biology, Department of Biochemistry and Molecular Biology, The University of Texas Houston Medical School, Houston, Texas 77030 and
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Fuerst O, Lin Y, Granell M, Leblanc G, Padrós E, Lórenz-Fonfría VA, Cladera J. The Melibiose Transporter of Escherichia coli: CRITICAL CONTRIBUTION OF LYS-377 TO THE STRUCTURAL ORGANIZATION OF THE INTERACTING SUBSTRATE BINDING SITES. J Biol Chem 2015; 290:16261-71. [PMID: 25971963 PMCID: PMC4481225 DOI: 10.1074/jbc.m115.642678] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2015] [Revised: 05/12/2015] [Indexed: 01/27/2023] Open
Abstract
We examine the role of Lys-377, the only charged residue in helix XI, on the functional mechanism of the Na(+)-sugar melibiose symporter from Escherichia coli. Intrinsic fluorescence, FRET, and Fourier transform infrared difference spectroscopy reveal that replacement of Lys-377 with either Cys, Val, Arg, or Asp disables both Na(+) and melibiose binding. On the other hand, molecular dynamics simulations extending up to 200-330 ns reveal that Lys-377 (helix XI) interacts with the anionic side chains of two of the three putative ligands for cation binding (Asp-55 and Asp-59 in helix II). When Asp-59 is protonated during the simulations, Lys-377 preferentially interacts with Asp-55. Interestingly, when a Na(+) ion is positioned in the Asp-55-Asp-59 environment, Asp-124 in helix IV (a residue essential for melibiose binding) reorients and approximates the Asp-55-Asp-59 pair, and all three acidic side chains act as Na(+) ligands. Under these conditions, the side chain of Lys-377 interacts with the carboxylic moiety of these three Asp residues. These data highlight the crucial role of the Lys-377 residue in the spatial organization of the Na(+) binding site. Finally, the analysis of the second-site revertants of K377C reveals that mutation of Ile-22 (in helix I) preserves Na(+) binding, whereas that of melibiose is largely abolished according to spectroscopic measurements. This amino acid is located in the border of the sugar-binding site and might participate in sugar binding through apolar interactions.
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Affiliation(s)
- Oliver Fuerst
- From the Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Yibin Lin
- From the Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Meritxell Granell
- From the Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Gérard Leblanc
- the Direction des Sciences du Vivant, Direction des progammes et valorization, CEA Fontenay-aux-Roses, 92265 Fontenay-aux-Roses Cedex, France, and
| | - Esteve Padrós
- From the Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
| | - Víctor A Lórenz-Fonfría
- From the Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain, Experimental Molecular Biophysics, Department of Physics, Freie Universität Berlin, 14195 Berlin, Germany
| | - Josep Cladera
- From the Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain,
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Kandori H, Furutani Y, Murata T. Infrared spectroscopic studies on the V-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1847:134-41. [PMID: 25111748 DOI: 10.1016/j.bbabio.2014.07.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2014] [Revised: 07/30/2014] [Accepted: 07/31/2014] [Indexed: 11/27/2022]
Abstract
V-ATPase is an ATP-driven rotary motor that vectorially transports ions. Together with F-ATPase, a homologous protein, several models on the ion transport have been proposed, but their molecular mechanisms are yet unknown. V-ATPase from Enterococcus hirae forms a large supramolecular protein complex (total molecular weight: ~700,000) and physiologically transports Na⁺ and Li⁺ across a hydrophobic lipid bilayer. Stabilization of these cations in the binding site has been discussed on the basis of X-ray crystal structures of a membrane-embedded domain, the K-ring (Na⁺ and Li⁺ bound forms). Sodium or lithium ion binding-induced difference FTIR spectra of the intact E. hirae V-ATPase have been measured in aqueous solution at physiological temperature. The results suggest that sodium or lithium ion binding induces the deprotonation of Glu139, a hydrogen-bonding change in the tyrosine residue and rigid α-helical structures. Identical difference FTIR spectra between the entire V-ATPase complex and K-ring strongly suggest that protein interaction with the I subunit does not cause large structural changes in the K-ring. This result supports the previously proposed Na⁺ transport mechanism by V-ATPase stating that a flip-flop movement of a carboxylate group of Glu139 without large conformational changes in the K-ring accelerates the replacement of a Na⁺ ion in the binding site. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems.
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Affiliation(s)
- Hideki Kandori
- Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan; OptoBioTechnology Research Center, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
| | - Yuji Furutani
- Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan; Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
| | - Takeshi Murata
- PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan; Department of Chemistry, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage, Chiba 263-8522, Japan
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