Crystal structure of the pantothenate synthetase from Mycobacterium tuberculosis, snapshots of the enzyme in action.

Pantothenate synthetase (PS) from Mycobacterium tuberculosis represents a potential target for antituberculosis drugs. PS catalyzes the ATP-dependent condensation of pantoate and beta-alanine to form pantothenate. Previously, we determined the crystal structure of PS from M. tuberculosis and its complexes with AMPCPP, pantoate, and pantoyl adenylate. Here, we describe the crystal structure of this enzyme complexed with AMP and its last substrate, beta-alanine, and show that the phosphate group of AMP serves as an anchor for the binding of beta-alanine. This structure confirms that binding of beta-alanine in the active site cavity can occur only after formation of the pantoyl adenylate intermediate. A new crystal form was also obtained; it displays the flexible wall of the active site cavity in a conformation incapable of binding pantoate. Soaking of this crystal form with ATP and pantoate gives a fully occupied complex of PS with ATP. Crystal structures of these complexes with substrates, the reaction intermediate, and the reaction product AMP provide a step-by-step view of the PS-catalyzed reaction. A detailed reaction mechanism and its implications for inhibitor design are discussed.