THE MICROTUBULE-ASSOCIATED PROTEIN-TAU IS EXTENSIVELY MODIFIED WITH O-LINKED N-ACETYLGLUCOSAMINE

Tau is a family of phosphoproteins that are important in modulating mi crotubule stability in neurons. In Alzheimer's disease tau is abnormal ly hyperphosphorylated, no longer binds microtubules, and self-assembl es to form paired helical filaments that likely contribute to neuron d eath. Here we demonstrate that normal bovine tau is multiply modified by Ser(Thr)-O-linked N-acetylglucosamine, a dynamic and abundant post- translational modification that is often reciprocal to Ser(Thr)phospho rylation. O-GlcNAcylation of tau was demonstrated by blotting with suc cinylated wheat germ agglutinin and by probing with bovine milk beta(1 ,4)galactosyltransferase. Structural analyses confirm the linkage and the saccharide structure. Tau splicing variants are multiply O-GlcNAcy lated at similar sites, with an average stoichiometry of greater than 4 mol of O-linked N-acetylglucosamine/mol of tau. However, the number of sites occupied appears to be greater than 12, suggesting substoichi ometric occupancy at any given site. A similar relationship between av erage stoichiometry and site-occupancy has also been described for the phosphorylation of tau. Site-specific or stoichiometric changes in O- GlcNAcylation may not only modulate tau function but may also play a r ole in the formation of paired helical filaments.