Biological studies of GPI-anchoring in Trypanosoma cruzi
Michele Anne Zacks
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Trypanosoma cruzi, a protozoan parasite transmitted to humans via triatomine\r\ninsects, causes chronic chagasic cardiomyopathy (CCM) in ~30% of infected individuals.\r\nThis dissertation sought to characterize T. cruzi’s pathogenic mechanisms by cellular,\r\nbiochemical, and molecular genetics approaches. In several protozoans, including T.\r\ncruzi, dominant cell surface proteins are attached to the parasite membrane by\r\nglycosylphosphatidylinositol (GPI) anchors and play roles in host cell attachment and\r\ninvasion, and in parasite differentiation and replication. In other organisms, a\r\ntransamidase, GPI8, is involved in this anchoring process. This study investigated the\r\neffects of protein-GPI depletion on T. cruzi growth and development by over-expressing\r\nTcGPI8 mutated in putative active site residues, which were determined based on\r\nsignificant homology to other GPI8s and plant endopeptidases containing conserved Cys\r\nand His residues in their active sites. In T. cruzi expressing TcGPI8 mutant alleles\r\n(C198A or H156A), no alteration in GPI-anchoring efficiency or impairment of in vitro\r\ninfectivity, differentiation or replication was observed. These results indicate that\r\nTcGPI8’s active site may not be comprised of H198A and C156A and, therefore, differs\r\nfrom that of yeast, human and Leishmania GPI8. Alternatively, targeted disruption of\r\nTcGPI8 in T. cruzi was employed to provide protein-GPI deficient mutants. Unintended\r\ndisruption of the GAPDH gene resulted from this approach and marked growth and\r\ndevelopmental defects were observed in these parasites at the epimastigote stage.