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Description

Posttranslational modification of proteins by beta-linked N-acetylglucosamine (beta-GlcNAc) via the hydroxyl moieties on serine or threonine residues is termed O-linked beta-GlcNAc or simply O-GlcNAc. O-GlcNAc is one of the most abundant posttranslational modifications within the nucleocytoplasmic compartments of all animals and plants. Unlike other types of protein glycosylations, O-GlcNAc occurs exclusively within the nuclear and cytoplasmic compartments and is generally not further modified to form more elongated structures. In addition, O-GlcNAcylation is a highly dynamic and reversible process. The O-GlcNAc transferase (OGT) attaches O-GlcNAc to proteins at specific serine or threonine residues, while O-GlcNAcase catalyzes the removal/hydrolysis of O-GlcNAc from proteins. In fact, a dynamic interplay between O-GlcNAcylation and serine/threonine phosphorylation plays an important role in regulating cellular signaling. Tau and RNA polymerase II (Pol II) are two well known proteins that undergo modification by O-GlcNAcylation. In Alzheimer's diseased human brains, tau becomes extensively phosphorylated and less O-GlcNAcylated. Similarly, O-GlcNAc is removed and replaced with O-phosphate on the Poly II CTD when the elongation phase of transcription is initiated.