1bjo

From Proteopedia

Revision as of 13:49, 5 November 2007

THE STRUCTURE OF PHOSPHOSERINE AMINOTRANSFERASE FROM E. COLI IN COMPLEX WITH ALPHA-METHYL-L-GLUTAMATE

Overview

Phosphoserine aminotransferase (PSAT; EC 2.6.1.52), a member of subgroup, IV of the aminotransferases, catalyses the conversion of, 3-phosphohydroxypyruvate to l-phosphoserine. The crystal structure of PSAT, from Escherichia coli has been solved in space group P212121 using MIRAS, phases in combination with density modification and was refined to an, R-factor of 17.5% (Rfree=20.1 %) at 2.3 A resolution. In addition, the, structure of PSAT in complex with alpha-methyl-l-glutamate (AMG) has been, refined to an R-factor of 18.5% (Rfree=25.1%) at 2.8 A resolution. Each, subunit (361 residues) of the PSAT homodimer is composed of a large, pyridoxal-5'-phosphate binding domain (residues 16-268), consisting of a, seven-stranded mainly parallel beta-sheet, two additional beta-strands and, seven alpha-helices, and a small C-terminal domain, which incorporates a, five-stranded beta-sheet and two alpha-helices. A three-dimensional, structural comparison to four other vitamin B6-dependent enzymes reveals, that three alpha-helices of the large domain, as well as an N-terminal, domain (subgroup II) or subdomain (subgroup I) are absent in PSAT. Its, only 15 N-terminal residues form a single beta-strand, which participates, in the beta-sheet of the C-terminal domain. The cofactor is bound through, an aldimine linkage to Lys198 in the active site. In the PSAT-AMG complex, Ser9 and Arg335 bind the AMG alpha-carboxylate group while His41, Arg42, and His328 are involved in binding the AMG side-chain. Arg77 binds the AMG, side-chain indirectly through a solvent molecule and is expected to, position itself during catalysis between the PLP phosphate group and the, substrate side-chain. Comparison of the active sites of PSAT and aspartate, aminotransferase suggests a similar catalytic mechanism, except for the, transaldimination step, since in PSAT the Schiff base is protonated., Correlation of the PSAT crystal structure to a published profile sequence, analysis of all subgroup IV members allows active site modelling of nifs, and the proposal of a likely molecular reaction mechanism.

About this Structure

1BJO is a Single protein structure of sequence from Escherichia coli with PLP as ligand. Active as Phosphoserine transaminase, with EC number 2.6.1.52 Structure known Active Sites: PPA and PPB. Full crystallographic information is available from OCA.

Reference

Crystal structure of phosphoserine aminotransferase from Escherichia coli at 2.3 A resolution: comparison of the unligated enzyme and a complex with alpha-methyl-l-glutamate., Hester G, Stark W, Moser M, Kallen J, Markovic-Housley Z, Jansonius JN, J Mol Biol. 1999 Feb 26;286(3):829-50. PMID:10024454

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