期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 104, 期 39, 页码 15294-15298出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0707688104
关键词
conformation; mechanism; membrane protein; transport; x-ray structure
资金
- Biotechnology and Biological Sciences Research Council [BB/C515163/1] Funding Source: Medline
- NIDDK NIH HHS [R01 DK051131, R56 DK051131, DK06946, DK51131] Funding Source: Medline
- NIGMS NIH HHS [1 U54 GM074929, 1 P50 GM073210, P50 GM073210, U54 GM074929] Funding Source: Medline
- Biotechnology and Biological Sciences Research Council [BB/C515163/1] Funding Source: researchfish
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.
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