title: Proton-coupled dynamics in lactose permease.
abstract: Lactose permease of Escherichia coli (LacY) catalyzes symport of a galactopyranoside and an H⁺ via an alternating access mechanism. The transition from an inward- to an outward-facing conformation of LacY involves sugar-release followed by deprotonation. Because the transition depends intimately upon the dynamics of LacY in a bilayer environment, molecular dynamics (MD) simulations may be the only means of following the accompanying structural changes in atomic detail. Here, we describe MD simulations of wild-type apo LacY in phosphatidylethanolamine (POPE) lipids that features two protonation states of the critical Glu325. While the protonated system displays configurational stability, deprotonation of Glu325 causes significant structural rearrangements that bring into proximity side chains important for H⁺ translocation and sugar binding and closes the internal cavity. Moreover, protonated LacY in phosphatidylcholine (DMPC) lipids shows that the observed dynamics are lipid-dependent. Together, the simulations describe early dynamics of the inward-to-outward transition of LacY that agree well with experimental data.
authors.affiliation: Department of Physiology and Biophysics and Center for Biomembrane Systems, University of California at Irvine, Irvine, CA 92697-4560, USA.
authors.forename: Magnus
authors.initials: M
authors.lastname: Andersson
authors.forename: Ana-Nicoleta
authors.initials: AN
authors.lastname: Bondar
authors.forename: J Alfredo
authors.initials: JA
authors.lastname: Freites
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Tobias
authors.forename: H Ronald
authors.initials: HR
authors.lastname: Kaback
authors.forename: Stephen H
authors.initials: SH
authors.lastname: White
mesh_terms: D004926:Escherichia coli / Q000201:enzymology; D026901:Membrane Transport Proteins / Q000737:chemistry*; D008958:Models, Molecular; D011522:Protons
chemical_list: D026901:Membrane Transport Proteins; D011522:Protons; C021499:lactose permease