Characterisation of phosphoglycerate kinase genes in Leishmania major and evidence for the absence of a third closely related gene or isoenzyme.

We have characterised the phosphoglycerate kinases (PGKs) in L. major and studied their mRNA and protein expression. Interestingly we have found evidence for only two tandemly linked PGK genes which correspond to the PGK gene B and C homologue in Trypanosoma and Crithidia. The primary structure of the leishmanial PGK genes B and C are virtually identical and differed only by the presence of a 62 amino acid extension at the carboxyl terminal of the PGK gene C homologue which is therefore likely to contain the translocation signal for glycosomal topogenesis. Indeed, the PGK gene C protein was found to be glycosomal (gPGK) while the PGK gene B protein was found to be cytosolic (cPGK). Both PGK genes are expressed in L. major promastigotes with the cPGK transcript expressed at a much higher level (4-5-fold) than the gPGK transcript. Similarly the relative cPGK isoenzyme activity was found to be approximately 4-fold higher than that of the gPGK isoenzyme. Surprisingly in L. major we have found no evidence for the PGK gene A present in all other trypanosomatids studied to date (Trypanosoma brucei, Trypanosoma congolense and Crithidia fasciculata). We therefore consider the possible evolutionary and functional significance of a trypanosomatid with only two PGK isoenzymes.