BRAIN PROLINE-DIRECTED PROTEIN-KINASE PHOSPHORYLATES TAU ON SITES THAT ARE ABNORMALLY PHOSPHORYLATED IN TAU ASSOCIATED WITH ALZHEIMERS PAIRED HELICAL FILAMENTS

Brain proline-directed protein kinase (BPDK), which contains a catalyt ic subunit homologous to and displaying site-specific phosphorylation similar to p34cdc2 kinase (Lew,J., Winkfein, R. J., Paudel, H. K., and Wang, J. H. (1992) J. Biol. Chem. 267, 25922-25926), has been examine d for possible involvement in tau phosphorylation. Immunoblot analyses using peptide antibodies specific for BPDK have revealed the presence of the kinase in bovine brain microtubules purified extensively by re peated polymerization and depolymerization cycles. When the microtubul e proteins are separated into the tubulin and microtubule-associated p rotein fractions, BPDK is found exclusively in the latter fraction. BP DK phosphorylates both tau and MAP2, the former protein being phosphor ylated to a stoichiometry of 3.8 mol of phosphate/mol of tau. Analysis of the phosphopeptides isolated from the tryptic digest of the phosph orylated bovine tau has revealed seven phosphorylation sites. Based on the sequence alignment between bovine and human tau proteins, these s ites correspond to Ser-195, Ser-202, Thr-205, Thr-231, Ser-235, Ser-39 6, and Ser-404 of human tau. Mass spectrometric analysis of the tau pr otein isolated from Alzheimer's paired helical filaments (PHFs) has de termined three abnormal phosphorylation sites and two phosphopeptides containing a total of five abnormal phosphates (Hasegawa, M., Morishim a-Kawashima, M., Takio, K., Suzuki, M., Titani, K., and Ihara, Y. (199 2) J. Biol. Chem. 267, 17047-17054). Two of the sites in tau phosphory lated by BPDK, Thr-231 and Ser-235, are among the abnormal phosphoryla tion sites, and the other sites phosphorylated by BPDK are within phos phopeptides from PHF-tau. These results suggest that BPDK may be one o f the kinases responsible for the abnormal phosphorylation-associated PHF-tau.