title: The role of interfacial lipids in stabilizing membrane protein oligomers.
abstract: Oligomerization of membrane proteins in response to lipid binding has a critical role in many cell-signalling pathways but is often difficult to define or predict. Here we report the development of a mass spectrometry platform to determine simultaneously the presence of interfacial lipids and oligomeric stability and to uncover how lipids act as key regulators of membrane-protein association. Evaluation of oligomeric strength for a dataset of 125 α-helical oligomeric membrane proteins reveals an absence of interfacial lipids in the mass spectra of 12 membrane proteins with high oligomeric stability. For the bacterial homologue of the eukaryotic biogenic transporters (LeuT, one of the proteins with the lowest oligomeric stability), we found a precise cohort of lipids within the dimer interface. Delipidation, mutation of lipid-binding sites or expression in cardiolipin-deficient Escherichia coli abrogated dimer formation. Molecular dynamics simulation revealed that cardiolipin acts as a bidentate ligand, bridging across subunits. Subsequently, we show that for the Vibrio splendidus sugar transporter SemiSWEET, another protein with low oligomeric stability, cardiolipin shifts the equilibrium from monomer to functional dimer. We hypothesized that lipids are essential for dimerization of the Na+/H+antiporter NhaA from E. coli, which has the lowest oligomeric strength, but not for the substantially more stable homologous Thermus thermophilus protein NapA. We found that lipid binding is obligatory for dimerization of NhaA, whereas NapA has adapted to form an interface that is stable without lipids. Overall, by correlating interfacial strength with the presence of interfacial lipids, we provide a rationale for understanding the role of lipids in both transient and stable interactions within a range of α-helical membrane proteins, including G-protein-coupled receptors.
authors.affiliation: Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA.
authors.forename: Kallol
authors.initials: K
authors.lastname: Gupta
authors.affiliation: Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA.
authors.forename: Joseph A C
authors.initials: JAC
authors.lastname: Donlan
authors.affiliation: Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA.
authors.forename: Jonathan T S
authors.initials: JTS
authors.lastname: Hopper
authors.affiliation: Centre for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, Stockholm SE-106 91, Sweden.
authors.forename: Povilas
authors.initials: P
authors.lastname: Uzdavinys
authors.affiliation: Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA.
authors.forename: Michael
authors.initials: M
authors.lastname: Landreh
authors.affiliation: Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA.
authors.forename: Weston B
authors.initials: WB
authors.lastname: Struwe
authors.affiliation: Centre for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, Stockholm SE-106 91, Sweden.
authors.forename: David
authors.initials: D
authors.lastname: Drew
authors.affiliation: Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Baldwin
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU.
authors.forename: Phillip J
authors.initials: PJ
authors.lastname: Stansfeld
authors.affiliation: Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA.
authors.forename: Carol V
authors.initials: CV
authors.lastname: Robinson
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D002308:Cardiolipins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D008024:Ligands; D008055:Lipids / Q000737:chemistry* / Q000494:pharmacology*; D013058:Mass Spectrometry / Q000379:methods*; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D034221:Moritella / Q000737:chemistry; D055503:Protein Multimerization / Q000187:drug effects*; D055550:Protein Stability / Q000187:drug effects; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry / Q000378:metabolism; D013816:Thermodynamics; D016963:Thermus thermophilus / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D002308:Cardiolipins; D029968:Escherichia coli Proteins; D008024:Ligands; D008055:Lipids; D008565:Membrane Proteins; C102839:NhaA protein, E coli; D043562:Receptors, G-Protein-Coupled; D017923:Sodium-Hydrogen Exchangers