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Publication Abstract from PubMed

Plants and bacteria assimilate sulfur into cysteine. Cysteine biosynthesis involves a bienzyme complex, the cysteine synthase complex (CSC), which consists of serine-acetyl-transferase (SAT) and O-acetyl-serine-(thiol)-lyase (OAS-TL) enzymes. The activity of OAS-TL is reduced by formation of the CSC. Although this reduction is an inherent part of the self-regulation cycle of cysteine biosynthesis, there has until now been no explanation as to how OAS-TL loses activity in plants. Complexation of SAT and OAS-TL involves binding of the C-terminal tail of SAT in one of the active sites of the homodimeric OAS-TL. We here explore the flexibility of the unoccupied active site in Arabidopsis thaliana cytosolic and mitochondrial OAS-TLs. Our results reveal two gates in the OAS-TL active site that define its accessibility. The observed dynamics of the gates show allosteric closure of the unoccupied active site of OAS-TL in the CSC, which can hinder substrate binding, abolishing its turnover to cysteine.

Allosterically Gated Enzyme Dynamics in the Cysteine Synthase Complex Regulate Cysteine Biosynthesis in Arabidopsis thaliana.,Feldman-Salit A, Wirtz M, Lenherr ED, Throm C, Hothorn M, Scheffzek K, Hell R, Wade RC Structure. 2012 Feb 8;20(2):292-302. PMID:22325778^[4]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.