glykolipidanker

glykolipidanker, or glycosylphosphatidylinositol (GPI) anchors, are carbohydrate–lipid structures that tether specific proteins to the outer leaflet of the plasma membrane. They are found in eukaryotes ranging from yeast to humans and mediate a variety of cellular functions such as signal transduction, cell adhesion, and immune recognition.

The core structure of a GPI anchor consists of a phosphatidylinositol lipid linked to a glycan chain that carries phosphoethanolamine. The glycan is usually a linear chain of N-acetylglucosamine and mannose residues, which may be further substituted with phosphoethanolamine and fatty acids that embed the anchor in the lipid bilayer. The tail of the GPI connects to the C‑terminus of the target protein through an amide bond.

Biosynthesis of GPI anchors occurs in the endoplasmic reticulum. It begins with the synthesis of the phosphatidylinositol–N‑acetylglucosamine intermediate, followed by a series of mannose and ethanolamine phosphate transfers. Once the anchor is attached to a nascent protein and the protein is processed by the ER quality‑control system, the complex is transported through the Golgi to the plasma membrane where it undergoes final trimming and remodeling.

GPI‑anchored proteins frequently localize to lipid rafts, specialized microdomains enriched in cholesterol and sphingolipids. This positioning facilitates interaction with signaling partners and allows rapid recycling or shedding from the cell surface. Loss of glycosylphosphatidylinositol biosynthesis is linked to a spectrum of human disorders, including paroxysmal nocturnal hemoglobinuria, inherited developmental diseases, and immune deficiencies, underscoring the importance of proper anchor formation for normal physiology.