Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 23, Pages 9361-9366Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1105687108
Keywords
bioenergetics; membrane protein crystal structure; MTS reagents; sugar binding; affinity labeling
Categories
Funding
- Human Frontier Science Program
- National Institutes of Health [DK051131, DK069463, GM073210, GM074929]
- National Science Foundation [0450970]
- Direct For Biological Sciences [0450970] Funding Source: National Science Foundation
- Div Of Molecular and Cellular Bioscience [0450970] Funding Source: National Science Foundation
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Lactose permease of Escherichia coli (LacY) with a single-Cys residue in place of A122 (helix IV) transports galactopyranosides and is specifically inactivated by methanethiosulfonyl-galactopyranosides (MTS-gal), which behave as unique suicide substrates. In order to study the mechanism of inactivation more precisely, we solved the structure of single-Cys122 LacY in complex with covalently bound MTS-gal. This structure exhibits an inward-facing conformation similar to that observed previously with a slight narrowing of the cytoplasmic cavity. MTS-gal is bound covalently, forming a disulfide bond with C122 and positioned between R144 and W151. E269, a residue essential for binding, coordinates the C-4 hydroxyl of the galactopyranoside moiety. The location of the sugar is in accord with many biochemical studies.
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