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X‐ray structure of glucose/galactose receptor from Salmonella typhimurium in complex with the physiological ligand, (2 R )‐glyceryl‐β‐ d ‐galactopyranoside
Author(s) -
Sooriyaarachchi Sanjeewani,
Ubhayasekera Wimal,
Boos Winfried,
Mowbray Sherry L.
Publication year - 2009
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2009.06945.x
Subject(s) - periplasmic space , galactose , monosaccharide , ligand (biochemistry) , biochemistry , receptor , chemistry , salmonella , stereochemistry , escherichia coli , bacteria , biology , gene , genetics
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‐β‐ d ‐galactopyranoside, solved by molecular replacement, and refined to 1.87 Å resolution with R and R ‐free values of 17% and 22%. The structure identifies three amino acid residues that are diagnostic of ( 2R )‐glyceryl‐β‐ 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‐β‐ d ‐galactopyranoside is the rule rather than the exception for receptors of this type. The role of ( 2R )‐glyceryl‐β‐ 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‐β‐ d ‐galactopyranoside] to the most open (an apo structure).