W0465

Structure of the S68A Mutant Reveals the Mechanism of Human S-AdoMetDC Proenzyme Processing. Yang Zhang¹, William D. Tolbert¹, Sarah E. Cottet¹, Eric M. Bennett¹, Jennifer L. Ekstrom¹, Anthony E. Pegg², Steven E. Ealick¹, ¹Dept. of Chemistry and Chemical Biology, Cornell Univ., Ithaca, NY, ²Depts. of Cellular and Molecular Physiology and Pharmacology, Milton S. Hershey Medical Center, Pennsylvania State Univ. College of Medicine, Hershey, PA.

S-adenosylmethionine decarboxylase (AdoMetDC) is an enzyme in the polyamine biosynthetic pathway. The product of its reaction, decarboxylated S-adenosylmethionine, is an aminopropyl group donor in the biosynthesis of spermidine and spermine. Polyamines are required for cell growth and the biosynthetic enzymes are targets for anti-cancer and anti-parasitic drugs. AdoMetDC levels are highly regulated through several mechanisms. AdoMetDC is synthesized as a protein precursor and is activated by an autocatalytic serinolysis reaction. A covalently attached pyruvoyl group is generated during the autoprocessing reaction and is utilized as a cofactor in the decarboxylation reaction. The mutation of Ser68 to alanine in human AdoMetDC prevents autoprocessing by removing the serine side chain necessary for nucleophilic attack at the adjacent carbonyl carbon atom. We have determined the crystal structure of S68A mutant and have constructed models of the proenzyme and intermediate. The structures of the S68A mutant and the models, together with the structures of the H243A mutant and the processed wild-type AdoMetDC, allowed us to identify key residues that are responsible for the autoprocessing reaction. Inhibition of the autoprocessing reaction is a possible strategy for anti-cancer drug design.