Oglykozylácia

Oglykozylácia is a post-translational modification where a glycosylphosphatidylinositol (GPI) anchor is attached to the C-terminus of a protein. This process allows proteins to be tethered to the outer surface of the cell membrane. The GPI anchor itself is a complex glycolipid consisting of a lipid moiety, a core oligosaccharide, and a phosphate group.

The addition of a GPI anchor typically occurs in the endoplasmic reticulum. A specific signal sequence at the C-terminus of the nascent polypeptide directs the protein to the ER membrane, where the anchor is attached by an enzyme complex. This modification is crucial for the proper localization and function of many cell surface proteins, including enzymes, adhesion molecules, and receptors.

Proteins with GPI anchors are not transmembrane proteins in the traditional sense, as they do not span the lipid bilayer with a hydrophobic protein sequence. Instead, their hydrophobic lipid tail is embedded in the membrane, allowing the rest of the protein to face the extracellular environment. This arrangement is important for signaling pathways and cell-cell interactions.

Disruptions in oglykozylácia can lead to various diseases. For example, paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired blood disorder caused by defects in the synthesis of the GPI anchor, leading to the deficiency of GPI-anchored proteins on blood cells. Understanding oglykozylácia is therefore vital for comprehending cellular biology and developing treatments for related disorders.