Functional characterization of enzymes involved in cysteine biosynthesis and H2S production in Trypanosoma cruzi

Trypanosoma cruzi is expected to synthetize de novo cysteine by different routes, among which the two-step pathway involving serine acetyltransferase and cysteine synthase (CS) is comprised. Also, cystathionine β synthase (CBS) might contribute to the de novo generation of cysteine in addition to catalyze the first step of the reverse transsulfuration route producing cystathionine. However, neither the functionality of CS nor that of cystathionine γ lyase (CGL) has been assessed. Our results show that T. cruzi CS could participate notably more actively than CBS in the de novo synthesis of cysteine. Interestingly, at the protein level T. cruzi CS is more abundant in amastigotes than in epimastigotes. Unlike the mammalian homologues, T. cruzi CGL specifically cleaves cystathionine into cysteine and is unable to produce H2S. The expression pattern of T. cruzi CGL parallels that of CBS, which unexpectedly suggests that in addition to the de novo synthesis of cysteine, the reverse transsulfuration pathway could be operative in the mammalian and insect stages. Besides, T. cruzi CBS produces H2S by decomposing cysteine or via condensation of cysteine with homocysteine. The latter reaction leads to cystathionine production, and is catalyzed remarkably more efficiently than the breakdown of cysteine. In T. cruzi like in other organisms, H2S could exert regulatory effects on varied metabolic processes. Notably, T. cruzi seems to count on stage-specific routes involved in cysteine production, the multiple cysteine-processing alternatives could presumably reflect this parasite's high needs of reducing power for detoxification of reactive oxygen species.

In Trypanosoma cruzi cystathionine β synthase (CBS), cystathionine γ lyase (CGL) and cysteine synthase (CS) are involved in cysteine generation, and noticeably CBS catalyses H2S production.105Highlights► Cysteine synthase exhibits higher catalytic competence than cystathionine β synthase in cysteine production. ► Cysteine synthase is more abundant in amastigotes but cystathionine β synthase is prevalent in promastigotes. ► Cystathionine β synthase produces H2S mainly by the condensation of cysteine and homocysteine. ► Cystathionine γ lyase specifically catalyses the cleavage of cystathionine into cysteine. ► The reverse transsulfuration pathway could be operative along the whole life cycle of T. cruzi.