title: Crystal structure of AlgQ2, a macromolecule (alginate)-binding protein of Sphingomonas sp. A1 at 2.0A resolution.
abstract: Sphingomonas sp. A1 possesses a high molecular mass (average 25,700 Da) alginate uptake system mediated by a novel pit-dependent ABC transporter. The X-ray crystallographic structure of AlgQ2 (57,200 Da), an alginate-binding protein in the system, was determined by the multiple isomorphous replacement method and refined at 2.0 A resolution with a final R-factor of 18.3% for 15 to 2.0 A resolution data. The refined structure of AlgQ2 was comprised of 492 amino acid residues, 172 water molecules, and one calcium ion. AlgQ2 was composed of two globular domains with a deep cleft between them, which is expected to be the alginate-binding site. The overall structure is basically similar to that of maltose/maltodextrin-binding protein, except for the presence of an N2-subdomain. The entire calcium ion-binding site is similar to the site in the EF-hand motif, but comprises a ten residue loop. This calcium ion-binding site is about 40 A away from the alginate-binding site.
authors.affiliation: Department of Basic and Applied Molecular Biotechnology, Division of Food and Biological Science, Graduate School of Agriculture, Kyoto University, Uji, 611-0011, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Momma
authors.forename: Bunzo
authors.initials: B
authors.lastname: Mikami
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Mishima
authors.forename: Wataru
authors.initials: W
authors.lastname: Hashimoto
authors.forename: Kousaku
authors.initials: K
authors.lastname: Murata
mesh_terms: D000464:Alginates / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D020832:EF Hand Motifs; D046911:Macromolecular Substances; D058619:Maltose-Binding Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D020578:Sphingomonas / Q000737:chemistry*; D014867:Water / Q000378:metabolism
chemical_list: D000464:Alginates; D001426:Bacterial Proteins; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D046911:Macromolecular Substances; D058619:Maltose-Binding Proteins; D014867:Water; D002118:Calcium