Protein O-GlcNAcylation: potential mechanisms for the regulation of protein function.

Abstract

Protein O-GlcNAcylation is the process whereby single N-acetylglucosamine residues are glycosidically linked to the hydroxyl side chains of specific serine and threonine residues. O-GlcNAc was originally identified while probing the surfaces of lymphocytes using UDP-[3H] galactose and highly purified galactosyltransferase (1). O-GlcNAc was not a substrate for galactosyltransferase unless the cell membrane was first disrupted with detergents indicating that it is an intracellular glycosylation. Subcellular fractionation further demonstrated that O-GlcNAc is found exclusively on nuclear and cytosolic proteins (2,3). Galactosyltransferase labeling of mouse liver nuclei with subsequent analysis by 2-dimensional gel electrophoresis and fluorography indicates that a large number of nuclear proteins are modified with O-GlcNAc residues and suggests that O-GlcNAc is as abundant as phosphorylation (4).