Poster: Hormones

Abs # 652: Crystal structures of ACC synthase in complex with AVG and PLP provide new insight into catalytic mechanism

Presenter:	Li, Ning
Authors	Huai, Qing  (A)   Xia, Yuanhong  (A)   Chen, Yongquan  (A)   Callahan, Brain  (A)   Li, Ning  (B)   Ke, Hengming  (A)
Affiliations:	(A): Department of Biochemistry and Biophysics and Lineberger Comprehensive Cancer Center, The University of North Carolina, Chapel Hill, NC 2759 (B): Hong Kong University Of Science Tech, Clear water bay, Hong Kong

The structures of tomato 1-aminocyclopropane-1-carboxylate synthase (ACS) complexed with either cofactor pyridoxal-5'-phosphate (PLP) or both PLP and inhibitor aminoethoxyvinylglycine have been determined by X-ray crystallography. The structures showed good conservation of the catalytic residues, suggesting a similar catalytic mechanism for ACS and other PLP-dependent enzymes. However, proximity of Tyr152 to the Cg-S bond of model substrate SAM implies its critical role in the catalysis. The concerted accomplishment of catalysis by cofactor PLP and a protein residue, as we proposed on basis of the ACS structures, may represent a general scheme for the diversity of PLP-dependent catalyses. PLP-dependent enzymes have been categorized into four types of folds. A structural comparison revealed that a core fragment of ACS in fold type I is superimposable over tryptophan synthase b subunit in fold type II and mammalian ornithine decarboxylase in fold type III, thus suggesting a divergent evolution of PLP-dependent enzymes.