title: X-ray structure of glucose/galactose receptor from Salmonella typhimurium in complex with the physiological ligand, (2R)-glyceryl-beta-D-galactopyranoside.
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 A 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).
authors.affiliation: Department of Molecular Biology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
authors.forename: Sanjeewani
authors.initials: S
authors.lastname: Sooriyaarachchi
authors.forename: Wimal
authors.initials: W
authors.lastname: Ubhayasekera
authors.forename: Winfried
authors.initials: W
authors.lastname: Boos
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Mowbray
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D005690:Galactose; D005697:Galactosides / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D012486:Salmonella typhimurium / Q000378:metabolism*; D016415:Sequence Alignment; D013237:Stereoisomerism
chemical_list: D001426:Bacterial Proteins; D005697:Galactosides; D008024:Ligands; D011956:Receptors, Cell Surface; C039707:galactose receptor; C027786:glucose receptor; C025100:isofloridoside; D005690:Galactose