title: Crystal structure of a periplasmic substrate-binding protein in complex with calcium lactate.
abstract: Lactate is utilized in many biological processes, and its transport across biological membranes is mediated with various types of transporters. Here, we report the crystal structures of a lactate-binding protein of a TRAP (tripartite ATP-independent periplasmic) secondary transporter from Thermus thermophilus HB8. The folding of the protein is typical for a type II periplasmic solute-binding protein and forms a dimer in a back-to-back manner. One molecule of l-lactate is clearly identified in a cleft of the protein as a complex with a calcium ion. Detailed crystallographic and biochemical analyses revealed that the calcium ion can be removed from the protein and replaced with other divalent cations. This characterization of the structure of a protein binding with calcium lactate makes a significant contribution to our understanding of the mechanisms by which calcium and lactate are accommodated in cells.
authors.affiliation: Department of Chemistry, Kyoto University, Sakyo-ku, Japan.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Akiyama
authors.forename: Kazuki
authors.initials: K
authors.lastname: Takeda
authors.forename: Kunio
authors.initials: K
authors.lastname: Miki
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D017610:Calcium Compounds / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D007773:Lactates / Q000737:chemistry* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D033902:Periplasmic Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding; D055503:Protein Multimerization; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016963:Thermus thermophilus / Q000737:chemistry
chemical_list: D017610:Calcium Compounds; D007773:Lactates; D026901:Membrane Transport Proteins; D033902:Periplasmic Binding Proteins; D021122:Protein Subunits; C110051:calcium lactate