Crystal Packing of Phosphopantetheine Adenylyltransferase from Mycobacterium tuberculosis in Two Crystal Modifications

Crystals of phosphopantetheine adenylyltransferase from Mycobacterium tuberculosis (PPATMt), which were grown using 2-methyl-2,4-pentanediol (MPD) or ammonium sulfate as the precipitant, belong to sp. grs. R32 and P3(2), respectively. Crystals of the enzyme containing the ligand in the active site were obtained by the cocrystallization of the enzyme with functional substrates only in the presence of MPD (sp. gr. R32). In the presence of ammonium sulfate, the ligand was not bound in the active site, and the cocrystallization resulted only in crystals of the apo form (sp. gr. P3(2)). The crystal-packing patterns of the enzyme molecules and the structure of the apo form of PPATMt in two crystal structures are compared in order to explain the binding patterns of the ligand in different crystal modifications. In the crystal modification P3(2), the molecules are more closely packed compared to the crystal modification R32, and intermolecular contacts restrict the access to the active site.