Structural determination of wild-type lactose permease

DOI: 10.1073/pnas.0707688104

Authors: L. Guan (University of California, USA) , O. Mirza (University of Copenhagen, Denmark) , G. Verner (University of California, USA.) , S. Iwata (Diamond Light Source) , H. R. Kaback (Imperial College London, U.K.)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Proceedings Of The National Academy Of Sciences , VOL 104 (39) , PAGES 15294 - 15298

State: Published (Approved)
Published: September 2007

Abstract: Here we describe an x-ray structure of wild-type lactose permease (LacY) from Escherichia coli determined by manipulating phospholipid content during crystallization. The structure exhibits the same global fold as the previous x-ray structures of a mutant that binds sugar but cannot catalyze translocation across the membrane. LacY is organized into two six-helix bundles with twofold pseudosymmetry separated by a large interior hydrophilic cavity open only to the cytoplasmic side and containing the side chains important for sugar and H+ binding. To initiate transport, binding of sugar and/or an H+ electrochemical gradient increases the probability of opening on the periplasmic side. Because the inward-facing conformation represents the lowest free-energy state, the rate-limiting step for transport may be the conformational change leading to the outward-facing conformation.

Journal Keywords: Conformation ; Mechanism ; Membrane Protein ; Transport ; X-Ray Structure

Subject Areas: Biology and Bio-materials

Facility: Advanced Light Source; Swiss Light Source