| Modification Notes |
Several cell surface proteins are attached to the membrane through their C-terminal domain and a glycosylphosphatidylinositol (GPI) moiety. Phosphatidylinositol-glycans (PIGs) are multi-pass transmembrane proteins that localize to the endoplasmic reticulum. PIGs are crucial for the synthesis of very early intermediates in GPI-anchor biosynthesis. PIG-Z (Phosphatidylinositol-glycan biosynthesis class Z protein), also known as GPI mannosyltransferase 4 and SMP3, is a 579 amino acid endoplasmic reticular protein that transfers the fourth mannose to some trimannosyl-GPIs during GPI precursor assembly. Since the presence of a fourth mannose in GPI is rarely detected, it is likely that it only exists in certain tissues. PIG-Z is widely expressed at very low levels, with highest expression in colon and brain. |