Abstract

Periplasmic binding proteins are abundant in bacteria by virtue of their essential roles as high-affinity receptors in ABC transport systems and chemotaxis. One of the best studied of these receptors is the so-called glucose/galactose-binding protein. Here, we report the X-ray structure of the Salmonella typhimurium protein bound to the physiologically relevant ligand, (2R)-glyceryl-beta-d-galactopyranoside, solved by molecular replacement, and refined to 1.87 angstrom resolution with R and R-free values of 17% and 22%. The structure identifies three amino acid residues that are diagnostic of (2R)-glyceryl-beta-d-galactopyranoside binding (Thr110, Asp154 and Gln261), as opposed to binding to the monosaccharides glucose and galactose. These three residues are conserved in essentially all available glucose/galactose-binding protein sequences, indicating that the binding of (2R)-glyceryl-beta-d-galactopyranoside is the rule rather than the exception for receptors of this type. The role of (2R)-glyceryl-beta-d-galactopyranoside in bacterial biology is discussed. Further, comparison of the available structures provides the most complete description of the conformational changes of glucose/galactose-binding protein to date. The structures follow a smooth and continuous path from the most closed structure [that bound to (2R)-glyceryl-beta-d-galactopyranoside] to the most open (an apo structure).

Keywords

galactose uptake; glucose; galactose-binding protein; glyceryl galactoside; lactose uptake; Salmonella enterica serovar Typhimurium

Published in

FEBS Journal
2009, volume: 276, number: 7, pages: 2116-2124
Publisher: WILEY-BLACKWELL PUBLISHING, INC

Authors' information