TRYPANOSOMA-CRUZI - IDENTIFICATION OF A MEMBRANE CYSTEINE PROTEINASE LINKED THROUGH A GPI ANCHOR

The biochemical and functional properties of T. cruzi GP50/55, a novel glycosylphosphatidylinositol (GPI)-anchored membrane antigen have bee n investigated. A 50-52-kDa thiol proteinase activity could be immunop recipitated with monoclonal antibodies (mAb) directed against GP50/55 (mAb C10), different from the one reactive with mAbs against lysosomal cysteine proteinase GP57/51. Furthermore,the mAb C10-reactive protein ase corresponded to the GPI-anchored surface antigen since the proteol ytic and antigenic activity partitioned to the aqueous phase after Tri ton X114 phase separation of phosphatidylinositol specific phospholipa se C (PI-PLC)-treated parasites. Of several proteins immunoprecipitate d by a polyclonal anti-lysosomal cysteine proteinase, an mAb to GP57/5 1 recognized a 60-kDa protein, whereas mAb C10 recognized antigens ran ging between 52 and 50 kDa. The GP50/55 antigen detected by mAb C10 is expressed on the parasite surface whereas the GP57/51 antigen is main ly intracellular. The internal peptide sequence obtained from purified GP50/55 showed that it is more homologous to the prototype of the cys teine proteinases superfamily, papain, than to the two T. cruzi lysoso mal cysteine proteinases so far described. Our data indicate that the T. cruzi GP50/55 is a novel GPI-anchored cysteine proteinase and may r epresent another isoform of this heterogeneous group of proteinases.