Discussion

Arginine methyltransferases (PRMTs) catalyze the post-translational methylation of a wide spectrum of proteins in different cellular processes. Remarkably, RNA-binding proteins (RBPs) are major substrates of PRMTs and modification may alter regulatory function. The Leishmania major genome encodes five PRMT homologs, including PRMT7, which is only found in a restricted group of eukaryotes. Both LmjPRMT7 expression and arginine monomethylation are tightly regulated during promastigote development; displaying procyclic stage-specific expression. In Ferreira et al., 2014 we demonstrated that LmjPRMT7 levels are inversely proportional to parasite virulence; the ∆lmjprmt7 null mutant led to an increased virulence, while LmjPRMT7-overexpressing parasites displayed attenuated virulence, both in vitro and in vivo. This work was the first to link PRMT enzymes with virulence and to describe a possible role of Leishmania methylation in the regulation of gene expression. We previously identified putative RBP substrates which co-immunoprecipitate with LmjPRMT7. Our biochemical analysis has now validated direct PRMT7 substrates and demonstrates monomethylation requires an intact PRMT7 catalytic domain and target protein RGG amino acid motifs. Results indicate LmjPRMT7 methylates Alba20 protein in vivo and reduced enzyme levels regulate expression of this and other RBP target proteins. We preliminarily present the Leishmania methylome for the first time and examine the impact of PRMT7 levels.