Two pathways for cysteine biosynthesis in Leishmania major

Roderick a M Williams , Gareth D Westrop , Graham H Coombs (1)

1 Strathclyde Institute of Pharmacy and Biomedical Sciences

Genome mining and biochemical analyses have shown that L. major possesses two pathways for cysteine synthesis - the de novo biosynthesis pathway comprising serine acetyltransferase (SAT) and cysteine synthase (CS) and the reverse transsulfuration (RTS) pathway comprising cystathionine β-synthase (CBS) and cystathionine gamma-lyase (CGL). The L. major CS (LmjCS) is similar to the type A CSs of bacteria and catalyses the synthesis of cysteine using O-acetyserine and sulfide with Kms of 17.5 and 0.13 mM, respectively. LmjCS can use sulfide provided by the action of mercaptopyruvate sulfurtransferase (MST) on 3-mercaptopyruvate (3-MP). LmjCS forms a bi-enzyme complex with Leishmania SAT (and Arabidopsis SAT), with residues K222, H226 and K227 of LmjCS being involved in the complex formation. LmjCBS catalyses the synthesis of cystathionine from homocysteine, but, unlike CBS of mammals, also has high cysteine synthase activity (but with the Km for sulfide being 10.7 mM). In contrast, LmjCS does not have CBS activity. CS was up-regulated when promastigotes are grown in medium with limited availability of sulfur amino acids. Exogenous methionine stimulated growth under these conditions and also the levels of intracellular cysteine, glutathione and trypanothione, whereas cysteine had no effect on growth or the intracellular cysteine levels; correlating with the low rate of transport of cysteine into the cell. These data suggest that cysteine is generated endogenously by promastigotes of Leishmania. The absence of CS from mammals and the clear differences between CBS of mammals and Leishmania suggest that each of the parasite enzymes could be a viable drug target.

Mots clés: Life Sciences

Roderick a M Williams, Gareth D Westrop, Graham H Coombs. Two pathways for cysteine biosynthesis in Leishmania major. Biochemical Journal, 2009, 420 (3), pp.451-462. ⟨10.1042/BJ20082441⟩. ⟨hal-00479145⟩