W0460

Structure of Human Phosphopantothenoylcysteine Synthetase. Narayanan Manoj, Erick Strauss, Tadhg Begley and Steven E. Ealick, Dept. of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853.

Coenzyme A is biosynthesized from phosphopantothenate in all organisms using four enzymatic steps. Phosphopantothenoylcysteine (PPC) synthetase catalyzes the first step. The structure of human phosphopantothenoylcysteine (PPC) synthetase was determined at 2.3 Å resolution. PPC synthetase is a dimer with identical monomers. Some features of the monomer fold resemble a group of NAD-dependent enzymes, while other features resemble the ribokinase fold. The ATP, phosphopantothenate and cysteine binding sites were deduced from modeling studies utilizing data from mutational analysis and location of highly conserved residues. The structure predicts a ping pong mechanism with initial formation of an acyladenylate intermediate, followed by release of pyrophosphate and attack by cysteine to form AMP and the final product PPC.