Biochemical characterization of enzymes involved in cysteine biosynthesis in Leishmania sp and Trypanosoma cruzi

MARCIANO DANIELA,; SANTANA, MARIANELA; NOWICKI , CRISTINA

Buzios, Brazil

Congreso; XIII International Congress of Protistology; 2009

Biochemical characterization of enzymes involved in cysteine biosynthesis in Leishmania sp and Trypanosoma cruzi. Marciano Daniela, Santana Marianela and Nowicki Cristina. Facultad de Farmacia y Bioquímica UBA, Buenos Aires, Argentina. cnowicki@criba.edu.ar. In TriTryps, the metabolism of sulfur-containing amino acid is complex and poorly understood yet. T. cruzi and Leishmania spp, but not T. brucei, might be able to assimilate in vivo inorganic sulfur to synthesize de novo cysteine. Different research groups reported that in both parasites two alternative routes might be operative involving, as in plants and bacteria, a serine acetyltransferase (SAT) and a cysteine synthase (CS), in addition to a broad specificity cystathionine beta synthase (CBS). The latter in vitro is capable to form cysteine by condensation of serine or O-acetylserine (OAS) with inorganic sulfide (IS). Nevertheless, in T. cruzi CS was not functionally characterized, and the operability of the putative SAT in Leishmania sp is still not well documented. Leishmanial and T. cruzi CSs closely resemble plant and bacterial enzymes; by contrast, SATs exhibit a non-conserved extension in their N-terminus yet the residues involved in catalysis are highly conserved in the C-terminal region. In this work we report the biochemical characterization of T. cruzi CS and leishmanial SAT. Both enzymes were cloned and functionally expressed in E. coli. The recombinant CS was highly specific towards OAS and IS whereas the leishmanial recombinant SAT catalyzed the O-acetylation of serine, and its specific activity highly resembled the values exhibited by plant SATs not complexed with CS.  Moreover, our results showed that T. cruzi and leishmanial CSs are cytosolic enzymes. The biological relevance of T. cruzi CS is strengthened since when compared with epimastigotes, the expression of CS is notably up-regulated in trypomastigotes and amastigotes.