Characterization of a protein with unknown function (LinJ.30.3360) in Leishmania amazonensis and Leishmania infantum

Leishmaniasis is a disease caused by trypanosomatid protozoa of the genus Leishmania. In the Americas, the species Leishmania amazonensis is predominantly associated with American cutaneous leishmaniasis (ACL) while L. infantum is an agent of visceral leishmaniasis (VL). The genome sequences of Leishmania spp. have shown that each genome can contain about 8000 genes encoding proteins, more than half of which have an unknown function (''hypotheticals") at the time of publication. To understand the biology and genome of the organisms, it is important to discover the function of these "hypothetical" proteins; however, few studies have focused on their characterizations. Previously, LinJ.30.3360 (a protein with unknown function) was identified as immunogenic to canine serum with VL and a good antigen to diagnose the visceral form in dogs. Here, we show that the LinJ.30.3360 protein is conserved in L. infantum, L. tarantolae, L. donovani, L. major, L. mexicana, L. braziliensis, L. panamensis, Leptomonas pyrrhocoris, and Leptomonas seymouri. It has been annotated as a MORN (Membrane Occupation and Recognition Nexus) domain protein. However, since the function of this motif is unknown, functional inferences based on the primary sequence are not possible. The protein has a folded β-leaf secondary structure, and phosphorylation was the only post-translational modification (PTM) found using prediction approach. Experiments have shown that it is located close to the flagellar pocket and presents similar abundance in both L. amazonensis and L. infantum. Furthermore, because it is a conserved protein in trypanosomatids but not in mammals and also because of its antigenicity, LinJ.30.3360 may constitute a potential drug target and/or vaccine for leishmaniasis.