Submitted on February 2, 2007
Revised on March 12, 2007
Accepted on March 13, 2007
GPI anchoring of protein in yeast and mammalian cells or: How we learned to stop worrying and love glycophospholipids
Peter Orlean and Anant K. Menon
Biochemistry, Weill Cornell Medical College, New York, NY 10021
Corresponding Author: akm2003{at}med.cornell.edu
Glycosylphosphatidylinositol (GPI) anchoring of cell surface proteins is the most complex and metabolically expensive of the lipid post-translational modifications described to date. The GPI anchor is synthesized via a membrane-bound multi-step pathway in the endoplasmic reticulum requiring more than 20 gene products. The pathway is initiated on the cytoplasmic side of the ER and completed in the ER lumen, necessitating flipping of a glycolipid intermediate across the membrane. The completed GPI anchor is attached to proteins that have been translocated across the ER membrane and which display a GPI signal anchor sequence at their C-terminus. GPI-proteins transit the secretory pathway to the cell surface; in yeast many become covalently attached to the cell wall. Genes encoding proteins involved in all but one of the predicted steps in the assembly of the GPI precursor glycolipid and its transfer to protein in mammals and yeast have now been identified. Most of these genes encode polytopic membrane proteins, some of which are organized in complexes. The steps in GPI assembly, and the enzymes that carry them out, are highly conserved. GPI biosynthesis is essential for viability in yeast and for embryonic development in mammals. In this review we describe the biosynthesis of mammalian and yeast GPIs, their transfer to protein, and their subsequent processing.
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