Phosphorylation sites on tau by tau protein kinase I, a bovine derived kinase generating an epitope of paired helical filaments.

Tau protein kinase I (TPKI) isolated from bovine brain has been determined to phosphorylate tau at four distinct sites by detecting modified Ser and Thr residues with protein sequencer. Ser199, Thr231, Ser396 and Ser413 were all found to have been phosphorylated by TPKI (numbering of amino acids was done in relation to the longest human tau [Neuron, 3 (1989) 519-526]). These phosphorylations generate an epitope of PHF (paired helical filaments) and eliminate the recognition of tau by the monoclonal antibody, tau-1. These results suggested that TPKI might be responsible for at least some of the phosphorylation of tau to induce PHF formation.