Crystal structure of Leishmania mexicana glycosomal glyceraldehyde-3-phosphate dehydrogenase in a new crystal form confirms the putative physiological active site structure.

The structure of glycosomal glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from the trypanosomatid parasite Leishmania mexicana in a new crystal form has been determined by X-ray crystallography. The protein crystallizes in space group P21 with one 156 kDa tetramer per asymmetric unit. The model of the protein with bound NAD+s and phosphates has been refined against 81% complete data from 10.0 to 2. 8 A to a crystallographic Rfactor of 0.217. The present structure confirms two key aspects of the previously reported orthorhombic crystal structure of L. mexicana GAPDH (LmGAPDH): the unusual conformation of a loop in the active site, and the repositioning of the inorganic phosphate binding site compared with crystal structures of GAPDHs from other organisms. As the monoclinic crystals of LmGAPDH were grown at a phosphate concentration and pH that were even closer to physiological conditions than were the orthorhombic LmGAPDH crystals, the present structure reinforces the physiological relevance of the active site structure seen in the previous orthorhombic crystal of LmGAPDH.