Component of the GPI transamidase complex. Essential for transfer of GPI to proteins, particularly for formation of carbonyl intermediates (By similarity). Glycolipid biosynthesis; glycosylphosphatidylinositol-anchor biosynthesis. Forms a complex with PIGK/GPI8, PIGS, PIGU and GPAA1/GAA1. Has a critical role in maintaining the complex by stabilizing the expression of GPAA1 and GPI8 and linking them to PIGS (By similarity). The disulfide bond between PIGK/GPI8 and PIGT is important for normal enzyme activity. Belongs to the PIGT family.