1.H.3. The 4 TMS Amastin (Amastin) Family
Amastin is a transmembrane glycoprotein found on the cell surfaces of trypanosomatid parasites. Encoded by a large, diverse gene family, amastin was initially described from the intracellular, amastigote stage of Trypanosoma cruzi and Leishmania donovani. Genome sequences subsequently showed that the amastin repertoire is much larger in Leishmania relative to Trypanosoma. Jackson 2010 sequenced the genomic regions containing amastin loci from two related insect parasites (Leptomonas seymouri and Crithidia sp.) and estimated the phylogeny for these and other amastin sequences. Amastin includes four subfamilies with distinct genomic positions, secondary structures, and evolution, which were already differentiated in the ancestral trypanosomatid. Diversification in Leishmania was initiated from a single ancestral locus on chromosome 34, with rapid derivation of novel loci through transposition and accelerated sequence divergence. This is absent from related organisms showing that diversification occurred after the origin of Leishmania. Some amastin genes may have evolved novel functions crucial to cell function in leishmanial parasites after the acquisition of a vertebrate host (Jackson 2010). Amastins may be virulence genes in Leishmania species (Azizi et al. 2009). Amastins have been used for vaccine development (Bolhassani et al. 2011).