Structural highlights
Function
[SERC_ECOLI] Catalyzes the reversible conversion of 3-phosphohydroxypyruvate to phosphoserine and of 3-hydroxy-2-oxo-4-phosphonooxybutanoate to phosphohydroxythreonine. Is involved in both pyridoxine and serine biosynthesis.[1] [2]
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
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.
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[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Lam HM, Winkler ME. Metabolic relationships between pyridoxine (vitamin B6) and serine biosynthesis in Escherichia coli K-12. J Bacteriol. 1990 Nov;172(11):6518-28. PMID:2121717
- ↑ Drewke C, Klein M, Clade D, Arenz A, Muller R, Leistner E. 4-O-phosphoryl-L-threonine, a substrate of the pdxC(serC) gene product involved in vitamin B6 biosynthesis. FEBS Lett. 1996 Jul 22;390(2):179-82. PMID:8706854
- ↑ Hester G, Stark W, Moser M, Kallen J, Markovic-Housley Z, Jansonius JN. 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. J Mol Biol. 1999 Feb 26;286(3):829-50. PMID:10024454 doi:http://dx.doi.org/10.1006/jmbi.1998.2506
