title: Interactions between phosphatidylethanolamine headgroup and LmrP, a multidrug transporter: a conserved mechanism for proton gradient sensing?
abstract: In a number of cases, the function of membrane proteins appears to require the presence of specific lipid species in the bilayer. We have shown that the secondary multidrug transporter LmrP requires the presence of phosphatidylethanolamine (PE), as its replacement by phosphatidylcholine (PC) inhibits transport activity and directly affects its structure, although the underlying mechanism was unknown. Here, we show that the effect of PE on the structure and the function of LmrP is mediated by interactions between the lipid headgroup and the protein. We used methyl-PE and dimethyl-PE analogs of PE to show that only replacement of the three hydrogens by methyl moieties leads to changes in the biochemical and biophysical properties of the reconstituted protein. This suggests that LmrP does not depend on the bulk properties of the phospholipids tested but solely on the hydrogen bonding ability of the headgroup. We then show that a single point mutation in LmrP, D68C, is sufficient to recapitulate precisely every biochemical and biophysical effect observed when PE is replaced by PC, including energy transfer between the protein tryptophan residues and the lipid headgroups. We conclude that the negatively charged Asp-68 is likely to participate in the interaction with PE and that such interaction is required for proton gradient sensing, substrate binding, and transport. Because Asp-68 belongs to a highly conserved motif in the Major Facilitator Superfamily (which includes LacY and EmrD), this interaction might be a general feature of these transporters that is involved in proton gradient sensing and lipid dependence.
authors.affiliation: Department of Structure and Function of Biological Membranes, Structural Biology and Bioinformatics Center, Université Libre de Bruxelles, CP206/2 Boulevard du Triomphe, Brussels, Belgium.
authors.forename: Pierre
authors.initials: P
authors.lastname: Hakizimana
authors.forename: Matthieu
authors.initials: M
authors.lastname: Masureel
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Gbaguidi
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Ruysschaert
authors.forename: Cédric
authors.initials: C
authors.lastname: Govaerts
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport / Q000502:physiology; D006860:Hydrogen Bonding; D013294:Lactococcus lactis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010713:Phosphatidylcholines / Q000737:chemistry* / Q000378:metabolism; D017354:Point Mutation; D018892:Proton-Motive Force / Q000502:physiology; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; D008051:Lipid Bilayers; C096807:LmrP protein, Lactococcus lactis; D026901:Membrane Transport Proteins; D010713:Phosphatidylcholines