CYSTEINE BIOSINTHESIS IN Leishmania PARASITES MIGHT INVOLVE ALTERNATIVE ROUTES

MARCIANO, DANIELA; SANTANA, MARIANELA; NOWICKI, CRISTINA

Rosario, Santa Fe, Argentina

Congreso; VIII Congreso Argentino de Protozoología y Enfermedades Parasitarias; 2008

Sociedad Argentina de Protozoología

 CYSTEINE BIOSYNTHESIS IN LEISHMANIA PARASITES MIGHT INVOLVE ALTERNATIVE ROUTES. Marciano D., Santana M. and Nowicki C. UBA-IQUIFIB-CONICET IIB-INTECH UNSAM, Buenos Aires, Argentina. daniela_marciano@yahoo.com.ar Cysteine is essential for the intracellular redox balance and oxidative detoxification. Plants, primitive eukaryotes and prokaryotes, unlike mammals, synthesize de novo cysteine. Serine acetyltransferase (SAT) and cysteine synthase (CS) are responsible for this process. The former catalyses the formation of O-acetylserine (OAS) whereas the latter condensates OAS with inorganic sulfide (IS). Cysteine can also be synthesized via cystathionine, in the first step, cystathionine beta synthase (CBS) condensates serine with homocysteine generating cystathionine, the precursor of cysteine synthesis in mammals. Since in TriTryps little is known about cysteine metabolism, we cloned the putative L. major SAT, CS and CBS. The three recombinant proteins were expressed in E. coli as soluble His-tagged enzymes. Leishmanial CS exhibits a cooperative behavior towards OAS and IS (Hills constants 2.7, 1.6 respectively), affinity constants of 1.5 mM for OAS and 3.6 mM for IS and a specific activity of 140 UE/mg. In Leishmania, CS activity was detected in the cytosol. Alternatively in L. major, synthesis of cysteine might depend on the functionality of CBS since the recombinant CBS is able to condensate IS with serine (13 UE/mg). However, leishmanial CBS showed to be more active catalyzing the production of cystathionine by the condensation of serine and homocysteine (35 UE/mg). The leishmanial CBS, unlike the mammalian enzyme, does not posses the hemo binding domain. Whether in Leishmania, cystathionine is converted into cysteine or/and methionine is still unknown, however unlike in mammals, the CS complex is functional and very likely responsible for de novo synthesis of cysteine. Moreover, CBS might also contribute to cysteine biosynthesis in this pathogen.