Structure of the GPI anchor. Phosphatidylinositol (PI) is inserted into the lipid bilayer of the plasma membrane. The glycan core, which contains the proaerolysin binding site, consists of a molecule of N-glucosamine (GlcNH₂), three manose molecules (Man) and a molecule of ethanolamine (EtN). The representative protein is covalently attached through an amide bond to an ethanolamine on the terminal mannose.