title: Salt-bridge dynamics control substrate-induced conformational change in the membrane transporter GlpT.
abstract: Active transport of substrates across cytoplasmic membranes is of great physiological, medical and pharmaceutical importance. The glycerol-3-phosphate (G3P) transporter (GlpT) of the E. coli inner membrane is a secondary active antiporter from the ubiquitous major facilitator superfamily that couples the import of G3P to the efflux of inorganic phosphate (P(i)) down its concentration gradient. Integrating information from a novel combination of structural, molecular dynamics simulations and biochemical studies, we identify the residues involved directly in binding of substrate to the inward-facing conformation of GlpT, thus defining the structural basis for the substrate-specificity of this transporter. The substrate binding mechanism involves protonation of a histidine residue at the binding site. Furthermore, our data suggest that the formation and breaking of inter- and intradomain salt bridges control the conformational change of the transporter that accompanies substrate translocation across the membrane. The mechanism we propose may be a paradigm for organophosphate:phosphate antiporters.
authors.affiliation: The Helen L. and Martin S. Kimmel Center for Biology and Medicine, Skirball Institute of Biomolecular Medicine, Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Law
authors.forename: Jonas
authors.initials: J
authors.lastname: Almqvist
authors.forename: Adam
authors.initials: A
authors.lastname: Bernstein
authors.forename: Regina M
authors.initials: RM
authors.lastname: Goetz
authors.forename: Yafei
authors.initials: Y
authors.lastname: Huang
authors.forename: Celine
authors.initials: C
authors.lastname: Soudant
authors.forename: Aatto
authors.initials: A
authors.lastname: Laaksonen
authors.forename: Sven
authors.initials: S
authors.lastname: Hovmöller
authors.forename: Da-Neng
authors.initials: DN
authors.lastname: Wang
mesh_terms: D000596:Amino Acids / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D017434:Protein Structure, Tertiary; D011522:Protons; D012965:Sodium Chloride / Q000737:chemistry*
chemical_list: D000596:Amino Acids; C488962:GlpT protein, E coli; D026901:Membrane Transport Proteins; D011522:Protons; D012965:Sodium Chloride