Structural basis for the feedback regulation of Escherichia coli pantothenate kinase by coenzyme A

Pantothenate kinase (PanK) is a key regulatory enzyme in the coenzyme A (Co A) biosynthetic pathway and catalyzes the phosphorylation of pantothenic ac id to form phosphopantothenate, CoA is a feedback inhibitor of PanK activit y by competitive binding to the ATP site. The structures of the Escherichia coli enzyme, in complex with a nonhydrolyzable analogue of ATP, 5'-adenyli mido-diphosphate (AMPPNP), or with CoA, were determined at 2.6 and 2.5 Angs trom respectively. Both structures show that two dimers occupy an asymmetri c unit; each subunit has a alpha/beta mononucleotide-binding fold with an e xtensive antiparallel coiled coil formed by two long helices along the dime rization interface. The two ligands, AMPPNP and CoA, associate with PanK in very different ways, but their phosphate binding sites overlap, explaining the kinetic competition between CoA and ATP, Residues Asp(127), His(177) a nd Arg(243) are proposed to be involved in catalysis, based on modeling of the pentacoordinate transition state. The more potent inhibition by CoA, co mpared with the CoA thioesters, is explained by a tight interaction of the CoA thiol group with the side chains of aromatic residues, which is predict ed to discriminate against the CoA thioesters. The PanK structure provides the framework for a more detailed understanding of the mechanism of catalys is and feedback regulation of PanK.