Role of two aminoacyl-tRNA synthetase associated proteins (Endothelial Monocyte Activating Polypeptides 1 and 2) of Leishmania donovani in chemotaxis of human monocytes.

Visceral leishmaniasis is caused by the protozoan parasite Leishmania donovani. It is a fatal form of leishmaniasis prevalent in Indian subcontinent. Since there are no human licensed vaccines available for leishmaniasis, chemotherapeutic drugs remain the only means for combating parasitic infections. We have earlier identified a total of 26 amino-acyl tRNA synthetases (aaRS) along with five stand-alone editing domains and two aaRS-associated proteins in Leishmania donovani. In addition to their canonical role of tRNA aminoacylation, aaRS have been involved in novel functions by acquiring novel domains during evolution. The aaRS-associated proteins have been reported to be analogous to a human cytokine, EMAP II, as they possess a modified version of the heptapeptide motif responsible for the cytokine activity. In this manuscript, we report the characterization of two L. donovani aminoacyl-tRNA synthetase associated proteins which showed a human chemokine like activity. Both the proteins, L. donovani EMAP-1 and EMAP-2, possess a modified form of the heptapeptide motif, which is responsible for cytokine activity in human EMAP-2. LdEMAP-1 and LdEMAP-2 were cloned, expressed, and purified. Both LdEMAP-1 and LdEMAP-2 proteins in the promastigote stage were found to be localized in cytoplasm as confirmed by immunofluorescence. In case of L. donovani infected human THP-1 derived macrophages, secretion of LdEMAP-1 and LdEMAP-2 proteins in the cytosol of the macrophages was observed. The role of LdEMAP-1 and LdEMAP-2 in the aminoacylation of rLdTyrRS was also tested and LdEMAP-2 but not LdEMAP-1 increased the rate of aminoacylation of tyrosyl tRNA synthetase (rLdTyrRS). L. donovani EMAP-1 and EMAP-2 proteins managed to exhibit the capability of attracting human origin cells as determined by chemotaxis assay, and also were able to induce the secretion of cytokines from macrophages like their human counterpart (EMAP II). Our working hypothesis is that both of these proteins might be involved in helping the parasite to establish the infection within the host.