1z7y
From Proteopedia
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Crystal Structure of the Arabidopsis thaliana O-Acetylserine Sulfhydrylase K46A mutant
Overview
In plants, cysteine biosynthesis plays a central role in fixing inorganic, sulfur from the environment and provides the only metabolic sulfide donor, for the generation of methionine, glutathione, phytochelatins, iron-sulfur, clusters, vitamin cofactors, and multiple secondary metabolites., O-Acetylserine sulfhydrylase (OASS) catalyzes the final step of cysteine, biosynthesis, the pyridoxal 5'-phosphate (PLP)-dependent conversion of, O-acetylserine into cysteine. Here we describe the 2.2 A resolution, crystal structure of OASS from Arabidopsis thaliana (AtOASS) and the 2.7 A, resolution structure of the AtOASS K46A mutant with PLP and methionine, covalently linked as an external aldimine in the active site. Although the, plant and bacterial OASS share a conserved set of amino acids for PLP, binding, the structure of AtOASS reveals a difference from the bacterial, enzyme in the positioning of an active site loop formed by residues 74-78, when methionine is bound. Site-directed mutagenesis, kinetic analysis, and, ligand binding titrations probed the functional roles of active site, residues. These experiments indicate that Asn(77) and Gln(147) are key, amino acids for O-acetylserine binding and that Thr(74) and Ser(75) are, involved in sulfur incorporation into cysteine. In addition, examination, of the AtOASS structure and nearly 300 plant and bacterial OASS sequences, suggest that the highly conserved beta8A-beta9A surface loop may be, important for interaction with serine acetyltransferase, the other enzyme, in cysteine biosynthesis. Initial protein-protein interaction experiments, using AtOASS mutants targeted to this loop support this hypothesis.
About this Structure
1Z7Y is a Single protein structure of sequence from Arabidopsis thaliana with AA5 as ligand. Active as Cysteine synthase, with EC number 2.5.1.47 Full crystallographic information is available from OCA.
Reference
Molecular basis of cysteine biosynthesis in plants: structural and functional analysis of O-acetylserine sulfhydrylase from Arabidopsis thaliana., Bonner ER, Cahoon RE, Knapke SM, Jez JM, J Biol Chem. 2005 Nov 18;280(46):38803-13. Epub 2005 Sep 15. PMID:16166087
Page seeded by OCA on Wed Nov 21 07:17:32 2007
