THE SWITCH OF TAU-PROTEIN TO AN ALZHEIMER-LIKE STATE INCLUDES THE PHOSPHORYLATION OF 2 SERINE PROLINE MOTIFS UPSTREAM OF THE MICROTUBULE BINDING REGION

The paired helical filaments (PHFs) of Alzheimer's disease consist mainly of the microtubule-associated protein tau. PHF tau differs from normal human brain tau in that it has a higher M(r) and a special state of phosphorylation. However, the protein kinase(s) involved, the phosphorylation sites on tau and the resulting conformational changes are only poorly understood. Here we show that a new monoclonal antibody, AT8, records the PHF-like state of tau in vitro, and we describe a kinase activity that turns normal tau into a PHF-like state. The epitope of AT8 is around residue 200, outside the region of internal repeats and requires the phosphorylation of serines 199 and/or 202. Both of these are followed by a proline, suggesting that the kinase activity belongs to the family of proline-directed kinases. The epitope of AT8 is nearly coincident with that of another phosphorylation-dependent antibody, TAU1 [Binder,L.I., Frankfurter,A. and Rebhun,L. (1985) J. Cell Biol., 101, 1371-1378], but the two are complementary since TAU1 requires a dephosphorylated epitope.