Where is the GPI anchor added to the target protein?

The GPI (glycosylphosphatidylinositol) anchor is added to target proteins in the endoplasmic reticulum (ER). This modification is a crucial post-translational event that attaches the protein to the cell membrane, facilitating its function as a membrane-bound protein.

In the ER, the GPI anchor is assembled and then added to specific proteins that are usually tagged for secretion or for residence on the cell surface. This process uses enzymes in the ER to ensure that the protein is correctly modified before it travels to its final destination within the cell membrane or is secreted outside of the cell.

Understanding that the GPI anchor is a specialized modification that occurs in the ER helps clarify the role of this organelle in processing and sorting proteins for their functional roles in cellular signaling, adhesion, and other important pathways.