CHARACTERIZATION OF IN-VITRO GLYCATION SITES OF TAU

Tau is a microtubule-associated protein that loses microtubule binding activity and aggregates into paired helical filaments (PHFs) in Alzhe imer's disease. Nonenzymic glycation is one of the posttranslational m odifications detected in PHF-tau, but not in normal tau. PHF-tau has r educed ability to bind to microtubules. To determine whether glycation of tau occurs in its microtubule binding domains, we have characteriz ed in vitro glycation sites of the longest isoform of tau, which has f our microtubule binding domains (Tau-4). The identified glycation site s are Lys-87, 132, 150, 163, 174, 225, 234, 259, 280, 281, 347, 353, a nd 369. We have also studied glycation of another isoform of tau, whic h has only three microtubule binding domains (Tau-3). This isoform is modified by glucose 15-20% more slowly than Tau-4. However, the glycat ion sites appear to be the same in both isoforms, except for Lys-280 a nd 281; these are located in the second microtubule binding domain, wh ich is missing in Tau-3. Lys-150, 163, and 174 are located within or p roximal to the sequence of tau that is involved in the microtubule nuc leation activity, and Lys-259, 280, 281, 347, 353, and 369 are located in the microtubule binding domains. Glycation at these sites can affe ct the functional properties of tau, and advanced glycation at these s ites might lead to the formation of insoluble aggregates similar to th e ones seen in Alzheimer's disease.