In silico identification of Leishmania GP63 protein epitopes to generate a new vaccine antigen against leishmaniasis

The surface of Leishmania spp. presents glycoprotein 63 (GP63), a metalloprotease that acts as one of the parasite's major antigens. A vaccine against leishmaniasis has not yet been developed and stationary phase promastigotes have utmost importance in transmitting Leishmania spp. from phlebotomine sand fly to humans or reservoirs. Therefore, this study aimed to analyze GP63 protein in three different Leishmania spp. to determine new vaccine candidate antigen against leishmaniasis using sequencing data of locally detected Leishmania strains and in silico approaches.

The GP63 protein sequences of the stationary phase/amastigote form of L. infantum, L. major, and L. tropica were identified and then the gene encoding GP63 protein in Leishmania positive samples (n:59) was amplified and sequenced for variation analysis. According to the results, 4, 6, 19 GP63 variants were found within L. infantum, L. major, and L. tropica isolates, respectively. The most prevalent variants within each species were selected for further analysis using in silico approaches. Accordingly, all selected GP63 proteins were antigenic and the amount of B and T cell epitopes were 23 for L. infantum, 10 for L. major, and 9 for L. tropica. The analysis of each epitope showed that all of them were non-toxic, non-allergen, and soluble but had different antigenicity values. Among these epitopes, EMEDQGSAGSAGS associated with L. major, STHDSGSTTC and AEDILTDEKRDILRK epitopes associated with L. infantum had the highest antigenicity values for B cell, MHC-I, and MHC-II epitopes, respectively. Moreover, conserved epitopes were detected among two or three Leishmania species.

This study detected many epitopes that could be used in vaccine studies and the development of serological diagnostic assays.