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Structural evidence for induced fit and a mechanism for sugar/H+ symport in LacY
Osman Mirza1, Lan Guan, Gill Verner
1Department of Biological Sciences, Membrane Protein Crystallography Group, Imperial College London, London, UK.
Abstract:
Cation-coupled active transport is an essential cellular process found ubiquitously in all living organisms. Here, we present two novel ligand-free X-ray structures of the lactose permease (LacY) of Escherichia coli determined at acidic and neutral pH, and propose a model for the mechanism of coupling between lactose and H+ translocation. No sugar-binding site is observed in the absence of ligand, and deprotonation of the key residue Glu269 is associated with ligand binding. Thus, substrate induces formation of the sugar-binding site, as well as the initial step in H+ transduction.
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