A potential target enzyme for trypanocidal drugs revealed by the crystal structure of NAD-dependent glycerol-3-phosphate dehydrogenase from Leishmania mexicana

Background: NAD-dependent glycerol-3-phosphate dehydrogenase (GPDH) catalyz es the interconversion of dihydroxyacetone phosphate and L-glycerol-3-phosp hate. Although the enzyme has been characterized and cloned from a number o f sources, until now no three-dimensional structure has been determined for this enzyme. Although the utility of this enzyme as a drug target against Leishmania mexicana is yet to be established, the critical role played by G PDH in the long slender bloodstream form of the related kinetoplastid Trypa nosoma brucei makes it a viable drug target against sleeping sickness. Results: The 1.75 Angstrom crystal structure of apo GPDH from L. mexicana w as determined by multiwavelength anomalous diffraction (MAD) techniques, an d used to solve the 2.8 Angstrom hole structure in complex with NADH. Each 39 kDa subunit of the dimeric enzyme contains a 189-residue N-terminal NAD- binding domain and a 156-residue C-terminal substrate-binding domain. Signi ficant parts of both domains share structural similarity with plant acetohy droxyacid isomeroreductase. The discovery of extra, fatty-acid like, densit y buried inside the C-terminal domain indicates a possible post-translation al modification with an associated biological function. Conclusions: The crystal structure of GPDH from L. mexicana is the first st ructure of this enzyme from any source and, in view of the sequence identit y of 63%, serves as a valid model for the T. brucei enzyme. The differences between the human and trypanosomal enzymes are extensive, with only 29% se quence identity between the parasite and host enzyme, and support the feasi bility of exploiting the NADH-binding site to develop selective inhibitors against trypanosomal GPDH. The structure also offers a plausible explanatio n for the observed inhibition of the T. brucei enzyme by melarsen oxide, th e active form of the trypanocidal drugs melarsoprol and cymelarsan.