Chapter 15 GPI Proteins in Biogenesis and Structure of Yeast Cell Walls

Abstract

I. Abstract Glycosyl phosphatidylinositol (GPI)‐anchored proteins have an uncommon function in yeasts and other ascomycete fungi: some of them are covalently incorporated into cell walls. Wall‐anchored GPI proteins include adhesins, cell wall structural proteins, and enzymes active in cell wall biogenesis and assembly, as well as nutrient acquisition. The wall cross‐linking is a result of cleavage of the GPI glycan between the glucosamine residue and the first mannose residue, followed by a transglycosylation reaction that links the reducing end of the GPI glycan remnant to the cell wall β1,6 glucan. Specific sequences in GPI proteins specify whether a GPI protein remains in the membrane, or is further processed and incorporated into the wall. Some GPI proteins are themselves transglycosidases active in wall assembly. GPI‐dependent cell wall anchorage is being exploited for surface display of exogenous peptides and proteins with great stability and high surface density. Such yeast surface displays include single‐chain antibodies and antigenic peptides, glycosidases for digestion of polysaccharides including cellulose, and lipases for both hydrolytic and synthetic reactions. Isolated walls with attached enzymes may be used as nonreproductive sources of enzymes or other proteins for bioremediation. Thus, the unique ability of yeasts to cross‐link GPI‐anchored proteins to the cell wall results from a unique metabolism, and has consequences for both fungal life‐styles and for use as a surface display platform. “Oh sweet and lovely wall …” [ 1 ]