Distinct sequence and structural feature of trypanosoma malate dehydrogenase.

Glycosomal malate dehydrogenase from Trypanosoma cruzi (tcgMDH) catalyzes the oxidation/reduction of malate/oxaloacetate, a crucial step of the glycolytic process occurring in the glycosome of the human parasite. Inhibition of tcgMDH is considered a druggable trait for the development of trypanocidal drugs. Sequence comparison of MDHs from different organisms revealed a distinct insertion of a prolin rich 9-mer (62-KLPPVPRDP-70) in tcgMDH as compared to other eukaryotic MDHs. Crystal structure of tcgMDH is solved here at 2.6 Å resolution with R/R values of 0.206/0.216. The tcgMDH forms homo-dimer with the solvation free energy (ΔG) gain of -9.77 kcal/mol. The dimeric form is also confirmed in solution by biochemical assays, chemical-crosslinking and dynamic light scattering. The inserted 9-mer adopts a structure of a solvent accessible loop in the vicinity of NAD binding site. The distinct sequence and structural feature of tcgMDH, revealed in the present report, provides an anchor point for the development of inhibitors specific for tcgMDH, possible trypanocidal agents of the future.