Heme A synthesis and CO activity are essential for infectivity and replication.

, the causative agent of Chagas disease, presents a complex life cycle and adapts its metabolism to nutrients' availability. Although is an aerobic organism, it does not produce heme. This cofactor is acquired from the host and is distributed and inserted into different heme-proteins such as respiratory complexes in the parasite's mitochondrion. It has been proposed that energy metabolism relies on a branched respiratory chain with a cytochrome oxidase-type 3 (CO) as the main terminal oxidase. Heme A, the cofactor for all eukaryotic CO, is synthesized via two sequential enzymatic reactions catalyzed by heme O synthase (HOS) and heme A synthase (HAS). Previously, TcCox10 and TcCox15 ( Cox10 and Cox15 proteins) were identified in They presented HOS and HAS activity, respectively, when they were expressed in yeast. Here, we present the first characterization of TcCox15 in , confirming its role as HAS. It was differentially detected in the different stages, being more abundant in the replicative forms. This regulation could reflect the necessity of more heme A synthesis, and therefore more CO activity at the replicative stages. Overexpression of a non-functional mutant caused a reduction in heme A content. Moreover, our results clearly showed that this hindrance in the heme A synthesis provoked a reduction on CO activity and, in consequence, an impairment on survival, proliferation and infectivity. This evidence supports that depends on the respiratory chain activity along its life cycle, being CO an essential terminal oxidase.