Oral Presentation 2014 International Biophysics Congress

Transport rates of a glutamate transporter homologue are determined by the lipid bilayer composition (#207)

Benjamin McIlwain 1 , Robert Vandenberg 1 , Renae Ryan 1
  1. Transporter Biology Group, University of Sydney, Camperdown, NSW, Australia

GltPh represents a paradigm for the human excitatory amino acid transporters (EAATs) and its structural determination has given insight into the mechanisms of ion-coupling and substrate sequestration. However, the crystal structures of GltPh have been solved in the absence of a lipid bilayer, and therefore cannot appreciate the wealth of interactions that take place between GltPh and the lipids of the membrane. We sought to determine whether the lipid bilayer composition influences rates of transport by reconstitutingGltPh into liposomes of defined lipid composition. Guided by similar studies on membrane transport proteins, we observed a striking influence on transport rates of GltPh depending on whether the primary lipid in the liposomes was phosphatidylethanolamine (PE) or its mono-, di- or tri- methyl derivatives. Analysis of the crystal structures of GltPh reveal a tyrosine residue (Y33) that we predict makes direct contact with the headgroup of membrane lipids and confers favourability to enter rate-determining intermediates of the transport cycle. Using site-directed mutagenesis we demonstrate that a cation-π interaction takes place between Y33 and the zwitterionic lipid headgroups. We propose that Y33 reports lipid bilayer composition to GltPh and this may offer a putative mechanism for GltPh to be coupled to the chemical composition of the lipid bilayer.

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