Glycosylphosphatidylinositol (GPI) anchor is a membrane attachment mechanism for
cell surface proteins widely used in eukaryotes. GPIs are added to
proteins posttranslationally by a complex
enzyme,
GPI transamidase. Previous studies have shown that human and Saccharomyces cerevisiae GPI
transamidases are similar and consist of five homologous components: GAA1, GPI8, PIG-S, PIG-T, and PIG-U in humans and Gaa1p, Gpi8p, Gpi17p, Gpi16p, and Cdc91p in S. cerevisiae. We report that
GPI transamidase of Trypanosoma brucei (Tb), a causative agent of
African sleeping sickness, shares only three components (TbGAA1, TbGPI8, and TbGPI16) with humans and S. cerevisiae but has two other specific components, trypanosomatid transamidase 1 (TTA1) and TTA2. GPI
transamidases of both bloodstream form (growing in mammalian blood) and procyclic form (growing in tsetse fly vector) of the parasite have the same five components. Homologues of TTA1 and TTA2 are present in Leishmania and Trypanosoma cruzi but not in mammals, yeasts, flies, nematodes, plants, or
malaria parasites, suggesting that these components may play unique roles in attachment of GPI anchors in trypanosomatid parasites and provide good targets for antitrypanosome drugs.