Component of the GPI transamidase complex. Involved in transfer of GPI to proteins (By similarity). Glycolipid biosynthesis; glycosylphosphatidylinositol-anchor biosynthesis. Forms a complex with PIG-S homolog, PIG-U homolog and GPI8. The disulfide bond between PIGK/GPI8 and PIGT is important for normal enzyme activity. Belongs to the PIGT family.