Glycosylphosphatidylinositol-anchored proteins (GPI-APs) are a diverse group of proteins that are attached to the cell membrane via a glycosylphosphatidylinositol anchor, playing crucial roles in various biological processes such as signal transduction, cell adhesion, and immune response. These proteins are synthesized in the endoplasmic reticulum, where they undergo post-translational modification, and are critical for proper cellular function and communication.