title: Three-dimensional structure of Escherichia coli branched-chain amino acid aminotransferase at 2.5 A resolution.
abstract: The X-ray crystallographic structure of the branched-chain amino acid aminotransferase from Escherichia coli was determined by means of isomorphous replacement using the selenomethionyl enzyme as one of the heavy atom derivatives. The enzyme is a homo hexamer with D3 symmetry, and the polypeptide chain of the subunit is folded into two domains (small and large domains). The coenzyme, pyridoxal 5'-phosphate, resides at the domain interface, its re-face facing toward the protein. The active site structure shows that the following sites can recognize branched-chain amino acids and glutamate as substrates: (1) a hydrophobic core formed by Phe36, Tyr164, Tyr31*, and Val109* for a branched-chain; (2) Arg97 for an acidic side chain of glutamate; and (3) Tyr95 and two main chain NH groups of Thr257 and Ala258 for the alpha-carboxylate of substrates. Although the main chain conformation of the active site is homologous to that of D-amino acid aminotransferase, many of the active site residues are different between them.
authors.affiliation: Department of Chemistry, Faculty of Science, Osaka City University, Sumiyoshi-ku, Osaka.
authors.forename: K
authors.initials: K
authors.lastname: Okada
authors.forename: K
authors.initials: K
authors.lastname: Hirotsu
authors.forename: M
authors.initials: M
authors.lastname: Sato
authors.forename: H
authors.initials: H
authors.lastname: Hayashi
authors.forename: H
authors.initials: H
authors.lastname: Kagamiyama
mesh_terms: D000410:Alanine Transaminase / Q000737:chemistry; D001665:Binding Sites; D018360:Crystallography, X-Ray; D051263:D-Alanine Transaminase; D004926:Escherichia coli / Q000201:enzymology*; D008958:Models, Molecular; D011487:Protein Conformation; D011732:Pyridoxal Phosphate / Q000378:metabolism; D000637:Transaminases / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D011732:Pyridoxal Phosphate; D000637:Transaminases; D000410:Alanine Transaminase; D051263:D-Alanine Transaminase; C019798:branched-chain-amino-acid transaminase