CYSTEINE BIOSYNTHEISIS IN LEISHMANIA PARASITES MIGHT INVOLVE ALTERNATIVE ROUTES.

MARCIANO, DANIELA; SANTANA, MARIANELA; NOWICKI , CRISTINA

Rosario Prov. Santa Fe, Argentina

Congreso; Sociedad Argentina de Protozoologia. XXIII Reunión Científica Anual; 2008

Sociedad Argentina de protozoologia

Cysteine is essential for many essential intracellular processes such as redox balance and the oxidative detoxification. Plants, primitive eukaryotes and prokaryotes, but not mammals, synthesize de novo cysteine. Cysteine synthase (CS) is responsible for the last step of this process, it condensates O-acetylserine with inorganic sulfide (IS). Alternatively, a closely related enzyme, cystathionine beta synthase (CBS) condensates serine with homocysteine generating cystathionine, which in mammals is converted into cysteine, however, in plants is a precursor for methionine biosynthesis. Since the enzymes involved in cysteine metabolism have been poorly studied in TriTryps, we cloned and expressed in E. coli L. major CS and CBS. The recombinant CS exhibits a specific activity of 140 UE/mg, when O-acetylserine (OAS) and IS were assayed, a cooperative behavior was observed for both substrates (Hills constants 2.7, 1.6 respectively) and affinity constants of 1.5 mM for OAS and 3.6 mM for IS were determined. Leishmanial CS is a cytosolic enzyme. Additionally, leishmanial CBS is also likely to be involved in cysteine biosynthesis since it is able to condensate IS and serine (specific activity of 13 UE/mg). However, this enzyme exhibits a higher catalytic competence when serine and homocysteine were assayed as substrates; the specific activity towards the production of cystathionine was 35 UE/mg. Our results show that in L. major de novo synthesis of cysteine might occur through different routes, via CS a typical plant enzyme, or via CBS which uses serine as carbon skeleton