Studies of enzymes involved in heme A biosynthesis in Trypanosoma cruzi.

CELESTE BUCHENSKY; PAULA ALMIRÓN; JULIA A CRICCO

Armação dos Búzios, RJ (Brasil)

Congreso; XIII International Congress of Protistology - XXV Annual Meeting of the Brazilian Society of Protozoology - XXXVI Annual Meeting on Basic Research in Chagas´Disease.; 2009

Brazilian Society of Protozoology

Studies of enzymes involved in heme A biosynthesis in Trypanosoma cruzi Celeste Buchensky1, Paula Almirón1 and  Julia A. Cricco*1,21Instituto de Biología Molecular y Celular de Rosario (IBR) Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET – Universidad Nacional de Rosario UNR, Argentina. 2Área Biofísica. Facultad de Ciencias Bioquímicas y Farmacéuticas UNR, Argentina. *cricco@ibr.gov.ar Heme A is an essential cofactor for eukaryotic cytochrome c oxidases. This cofactor is derived from heme B via two enzymatic reactions. The first one, catalyzed by heme O synthase (HOS, Cox10p), results in the conversion of the vinyl group on pyrrole ring A into a 17-hydroxyethylfarnesyl moiety. In the second transformation, heme A synthase (HAS, Cox15p) catalyzes the oxidation of the methyl group on pyrrole ring D into an aldehyde. The biosynthesis of this cofactor is carried out in the mitochondria, and HOS and HAS enzymes are encoded by nuclear genes COX10 y COX15 respectively. Although T. cruzi does not synthesize heme de novo, we have identified by sequence homology searches the open reading frames for putative Cox10p and Cox15p enzymes. To assign the function of above mentioned genes (TcCOX10 and TcCOX15), they were cloned and expressed in S. cerevisiae cox10 and cox15 knock out cells respectively (cox10D and cox15D). These mutant cells are respiratory deficient and show impaired heme A biosynthesis. The expression of TcCox10  and TcCox15 in yeast mutants suppresses the phenotype of the knock out cells, restoring the standard levels of respiratory activity and mitochondrial heme A concentration. These results support that T. cruzi presents a heme A biosynthetic pathway. In addition, these data are in agreement with early studies showing the aa3 type of cytochrome c oxidase as a main oxidase in epimastigotes and the fact that recent proteomic reports revealed the presence of different subunits of cytocrome c oxidase in epimastigotes and trypomastigotes forms. Notwithstanding this parasite does not synthesize heme, the presence of Cox10p and Cox15p enzymes and other hemoproteins suggest that this cofactor has to be imported and transported into the mitochondria, where it is modified in order to be utilized by hemoproteins involved in key processes.Supported by: CONICET.