PMID: 21593407

Authors:

Chaptal V, Kwon S, Sawaya MR, Guan L, Kaback HR, Abramson J

Title:

Crystal structure of lactose permease in complex with an affinity inactivator yields unique insight into sugar recognition.

Journal:

Proc Natl Acad Sci U S A. 2011 Jun 7;108(23):9361-6. Epub 2011 May 18.

Abstract:

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.