Structural highlights
Publication Abstract from PubMedPlants produce cyanide (CN(-)) during ethylene biosynthesis in the mitochondria and require beta-cyanoalanine synthase (CAS) for CN(-) detoxification. Recent studies show that CAS is a member of the beta-substituted alanine synthase (BSAS) family, which also includes the Cys biosynthesis enzyme O-acetylserine sulfhydrylase (OASS), but how the BSAS evolved distinct metabolic functions is not understood. Here we show that soybean (Glycine max) CAS and OASS form alpha-aminoacrylate reaction intermediates from Cys and O-acetylserine, respectively. To understand the molecular evolution of CAS and OASS in the BSAS enzyme family, the crystal structures of Gm-CAS and the Gm-CAS K95A mutant with a linked pyridoxal phosphate (PLP)-Cys molecule in the active site were determined. These structures establish a common fold for the plant BSAS family and reveal a substrate-induced conformational change that encloses the active site for catalysis. Comparison of CAS and OASS identified residues that covary in the PLP binding site. The Gm-OASS T81M, S181M, and T185S mutants altered the ratio of OASS:CAS activity but did not convert substrate preference to that of a CAS. Generation of a triple mutant Gm-OASS successfully switched reaction chemistry to that of a CAS. This study provides new molecular insight into the evolution of diverse enzyme functions across the BSAS family in plants. Structure of Soybean beta-Cyanoalanine Synthase and the Molecular Basis for Cyanide Detoxification in Plants.,Yi H, Juergens M, Jez JM Plant Cell. 2012 Jun;24(6):2696-706. Epub 2012 Jun 26. PMID:22739827[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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