The identification and molecular characterization of Trypanosoma cruzi amastigote surface protein-1, a member of the trans-sialidase gene super-family

An accumulating body of evidence suggests that T. cruzi-infected host cells are recognized and destroyed by class I major histocompatibility complex (MHC) restricted CD8⁺ T-cells thus contributing to immune control of the infection. However, to date, only a few amastigote proteins which could be the target of this response have been described and gene sequence information is available only for the amastins. In order to identify amastigote proteins which could contribute to immune detection of infected host cells, a panel of monoclonal antibodies specific for amastigote proteins was produced and screened. Three mAbs (IIIC4, VIIC1 and IIID4) were identified which recognized amastigote surface proteins of 78, 26 and 53 kDa, respectively. Screening of an amastigote cDNA expression library with mAb IIIC4 resulted in the isolation of a 2.8 Kb clone, pS12. The derived amino acid sequence indicates that the pS12 clone encodes an amastigote surface protein belonging to the T. cruzi trans-sialidase super-family. Based on its preferential expression in the amastigote stage we have named this protein amastigote surface protein-1 (ASP-1). ASP-1 contains the third and fourth Asp block motifs, SxDxGxTW and the fibronectin type III-like domain, VTVxNVxLYNR, thus placing it in family II of the T. cruzi trans-sialidases. ASP-1 is the first trans-sialidase family member shown to be preferentially expressed in the amastigote stage of the T. cruzi life cycle. This expression of ASP-1 on parasites in infected cells and its apparent membrane attachment by a glycosylphosphatidylinositol (GPI)-anchor makes it a prime candidate to enter the class I MHC processing and presentation pathway.