GPAA1 (glycosylphosphatidylinositol anchor attachment 1) is a catalytic subunit of the GPI transamidase (GPIT) complex located in the endoplasmic reticulum 1. As a metallo-peptidase component, GPAA1 catalyzes the covalent attachment of GPI lipid anchors to substrate proteins, a post-translational modification essential for anchoring numerous cell surface proteins to the plasma membrane 2. Structurally, GPAA1 functions as a zinc-dependent metallopeptidase with two large flaps surrounding its active site that restrict substrate access 2. Beyond its canonical biosynthetic role, GPAA1 has emerged as a significant oncogenic factor. GPAA1 is overexpressed in multiple cancers including colorectal, gastric, and hepatocellular carcinoma, promoting tumor progression and metastasis 345. Notably, GPAA1 facilitates surface expression of CD24, an immune checkpoint "don't eat me" signal that prevents macrophage-mediated phagocytosis in ovarian cancer 67. Targeting GPAA1 with the aminopeptidase inhibitor bestatin reduces CD24 surface expression and enhances anti-tumor immunity 6. Mutations in GPAA1 cause glycosylphosphatidylinositol biosynthesis defect 15, establishing clinical relevance to GPI-anchor assembly disorders.