The apical sorting of glycosylphosphatidylinositol-linked proteins

Many cells, from yeast to human, use glycosylated form of phosphatidylinositol to anchor proteins to the cell surface. Several terms have been coined to describe this anchoring mechanism. They include “glycosylphosphatidylinositol (GPI) anchoring,” “glypiation,” “phosphatidylinositol-glycan (PIG) tailing,” and “greasy foot.” All GPI anchors contain a conserved glycan core structure, composed of ethanolamine, phosphate, mannose, glucosamine, and inositol, whereas GPI-linked proteins are found clustered in caveolae, a specialized domain of the plasma membrane. This chapter discusses the reasons for GPI-linked proteins being selectively transported to the apical surface of polarized epithelial cells, with GPI acting as a dominant apical trafficking signal.