Lessons from lactose permease.

Lan Guan; H Ronald Kaback

doi:10.1146/annurev.biophys.35.040405.102005

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Lessons from lactose permease.

Lan Guan·H Ronald Kaback

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Abstract

An X-ray structure of the lactose permease of Escherichia coli (LacY) in an inward-facing conformation has been solved. LacY contains N- and C-terminal domains, each with six transmembrane helices, positioned pseudosymmetrically. Ligand is bound at the apex of a hydrophilic cavity in the approximate middle of the molecule. Residues involved in substrate binding and H+ translocation are aligned parallel to the membrane at the same level and may be exposed to a water-filled cavity in both the inward- and outward-facing conformations, thereby allowing both sugar and H+ release directly into either cavity. These structural features may explain why LacY catalyzes galactoside/H+ symport in both directions utilizing the same residues. A working model for the mechanism is presented that involves alternating access of both the sugar- and H+-binding sites to either side of the membrane.

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Binding Sites Biological Transport, Active Enzyme Activation Enzyme Stability Escherichia coli Proteins Hydrogen-Ion Concentration Ion Channel Gating Models, Biological Models, Chemical Models, Molecular Monosaccharide Transport Proteins Monosaccharides Protein Binding Protein Conformation Structure-Activity Relationship Symporters Journal Article Review

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Lan Guan, H Ronald Kaback. 2006. Lessons from lactose permease.. https://doi.org/10.1146/annurev.biophys.35.040405.102005

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