Biochemical characterization of the three enzymes involved in the two routes of cysteine biosynthesis in Trypanosoma cruzi and Leishmania sp.

MARCIANO DANIELA; SANTANA, MARIANELA; NOWICKI , CRISTINA

Santa Fé, Prov. Santa Fé

Congreso; XXIII Reunión Científica Anual, Sociedad Argentina de de Protozoología; 2009

Sociedad Argentina de de Protozoología

Daniela Marciano, Marianela Santana, Cristina Nowicki. Instituto de Química y Fisicoquímica Biológica IQUIFIB-CONICET, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, C1113AAD, Buenos Aires, Argentina. daniela_marciano@yahoo.com.ar Cysteine plays key biological roles in all organisms, moreover in trypanosomatids, is essential for biosynthesis of trypanothione, which is crucial in the defense against oxidative stress. In Trypanosoma cruzi and Leishmania spp, but not in T. brucei, two pathways for de novo synthesis of cysteine are expected to be operative and three enzymes to be involved: serine acetyltransferase (SAT), cysteine synthase (CS) and cystathionine b synthase (CBS). Our results demonstrated the functionality of L. major SAT (LmjF34.2850) and T. cruzi CS (Tc00.1047053507165.50). Leishmanial SATs are highly conserved proteins with unusually extended N-termini, presumably are homotrimeric molecules and their subunits exhibit the highest apparent molecular masses (45 kDa) among the members of SATs family. L. major SAT appeared to be capable to specifically interact and be activated by homologous CS. However, whether both proteins form a plausible bi-enzyme complex, with similar roles as those described for plant and bacteria counterparts remain unclear yet. T. cruzi CS shares a notable sequence similarity with leishmanial and plant homologues. Consistently, T. cruzi and L. major CSs exhibited a notably high binding affinity for OAS (1mM and 8mM, respectively). T. cruzi and leishmanial CSs and CBSs are cytosolic enzymes hence, the last steps of both cysteine biosynthetic routes occur in the same subcellular compartment. CS might produce cysteine using OAS as carbon backbone, whereas CBS might preferentially utilize serine as precursor for cysteine biosynthesis. This redundant capability very likely reflects the vital role cysteine fulfills along the different nutritional and oxidative stress conditions these parasites have to face during their life cycles. As predicted for Leishmania parasites, also T. cruzi CS is notably more abundant in the mammalian stages than in the insect stage of this pathogen. SAT and CS are absent in mammals, and the CBSs from both parasites notably differ from the mammalian counterpart. Hence, the three enzymes might represent potential chemotherapeutic targets.