Abstract
Coenzyme A (CoA) is the principle acyl carrier in all living cells, and is required for many metabolic reactions, including citric acid cycle and fatty acid metabolism. Phosphopantetheine adenylyltransferase (PPAT; EC: 2.7.7.3) is an essential enzyme that catalyzes the penultimate step of CoA biosynthesis by transferring an adenylyl group from ATP to 4’-phosphopantetheine (Ppant), yielding 3’-dephospho-CoA (dPCoA) and pyrophosphate. PPAT catalyzes the second rate-limiting step in CoA synthetic pathway and is regulated by feedback inhibition by downstream end product, CoA. The bacteria PPAT sequences show high degree of homology but are dissimilar from mammalian, therefore, this enzyme might be a good antibacterial target. PPAT from Helicobacter pylori (H. pylori) which infects about 50% world population and cause gastric and duodenal ulcers was expressed and crystallized in space group I222. The crystal structure of H. pylori PPAT has been determined by molecular replacement method at 1.75 Å resolution. The structure shows an open form of H. pylori PPAT that have not been observed in other PPATs. Since previous reports have shown that PPAT from Escherichia coli exhibites pH-dependent binding affinity towards substrates, the PPAT structural stability and activity was studied by circular dichroism and isothermal titration calorimetry.