THE CRYSTAL-STRUCTURE OF TRYPANOTHIONE REDUCTASE FROM THE HUMAN PATHOGEN TRYPANOSOMA-CRUZI AT 2.3 ANGSTROM RESOLUTION

Trypanothione reductase (TR) is an NADPH-dependent flavoprotein unique to protozoan parasites from the genera era Trypanosoma and Leishmania and is an important target for the design of improved trypanocidal dr ugs. We present details of the structure of TR from the human pathogen Trypanosoma cruzi, the agent responsible for Chagas' disease or South American trypanosomiasis. The structure has been solved by molecular replacement, using as the starting model the structure of the enzyme f rom the nonpathogenic Crithidia fasciculata, and refined to an R-facto r of 18.9% for 53,868 reflections with F greater than or equal to sigm a F between 8.0 and 2.3 Angstrom resolution. The model comprises two s ubunits (968 residues), two FAD prosthetic groups, two maleate ions, a nd 419 water molecules. The accuracy and geometry of the enzyme model is improved with respect to the C. fasciculata enzyme model. The new s tructure is described and specific features of the enzyme involved in substrate interactions are compared with previous models of TR and rel ated glutathione reductases from human and Escherichia coli. Structura l differences at the edge of the active sites suggest an explanation F or the differing specificities toward glutathionylspermidine disulfide .