Glycosyl phosphatidylinositol-linked glycoconjugates: structure, biosynthesis and function.

The purpose of this review is to summarize the most recent advances on GPI research. Structural studies on GPI-linked glycoconjugates indicate that there are significant variations in different organisms, although there is a conserved core structure. Furthermore, structural studies suggest that in different cell types, there is an army of glycosyltransferases dedicated to the synthesis of GPI-linked glycoconjugates. Biochemical studies on the synthesis of these GPI-linked glycoconjugates suggest that not only many different enzymes are involved but also that enzymes from different cell types, involving in the conserved core structure can have different substrate specificity. Genetic cloning of the yeast genes involved in synthesizing the core structure suggests that many of these enzymes also have human homologues. However, paroxysmal nocturnal hemogobinuria (PNH) is the only known human disease associated with the synthesis of GPI-linked glycoconjugates. Functional studies suggest that GPI-anchor can act as a signal for protein sorting and localization. Furthermore, GPI-linked receptors play an important role in T-cell activation.