MONOCLONAL-ANTIBODY PHF-1 RECOGNIZES TAU-PROTEIN PHOSPHORYLATED AT SERINE RESIDUE-396 AND RESIDUE-404

The microtubule-associated protein tau is hyperphosphorylated in the paired helical filaments (PHFs) of Alzheimer's disease, Immunological and direct chemical studies have identified Ser(396) and Ser(404) as two of the phosphorylated sites, Previously, we have demonstrated, using synthetic tau peptides containing phosphorylated Ser(396), that this site is recognized by the monoclonal antibody PHF-1. The present study extends this observation by showing that PHF-1 recognizes tau peptides containing either individually phosphorylated Ser(396) or Ser(404), but that there is a >10-fold increase in the sensitivity of detection of tau peptides by PHF-1 when both serines are phosphorylated, The recognition of singly or doubly phosphorylated Ser(396) and Ser(404) in tau by PHF-1 can also be demonstrated in Chinese hamster ovary cells transfected with full-length wild-type tau constructs or mutant constructs with Ala substituted for Ser(396) or Ser(404), We conclude that the PHF-1 epitope contains both phosphorylated Ser(396) and Ser(404). (C) 1994 Wiley-Liss, Inc.