Trypanosoma cruzi glycosomal glyceraldehyde-3-phosphate dehydrogenase:: structure, catalytic mechanism and targeted inhibitor design

The structure of the enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from glycosomes of the parasite Trypanosoma cruzi, causative agent of Chagas' disease, is reported. The final model at 2.8 Angstrom includes the bound cofactor NAD(+) and 90 water molecules per monomer and resulted in an R-factor of 20.1%, R-free = 22.3%, with good geometry indicators. The structure has no ions bound at the active site resulting in a large change in the side chain conformation of Arg(249) which as a consequence forms a salt bridge to Asp(210) in the present structure. We propose that this conformational change could be important for the reaction mechanism and possibly a common feature of many GAPDH structures. Comparison with the human enzyme indicates that interfering with this salt bridge could be a nem approach to specific inhibitor design, as the equivalent to Asp(210) is a leucine in the mammalian enzymes. (C) 1998 Federation of European Biochemical Societies.