Fetal‐Type Phosphorylation of the τ in Paired Helical Filaments

Abstract

To determine the phosphorylation sites of the τ in paired helical filaments (PHF), two types of PHF antisera with different specificities were used: One was a conventional anti‐PHF, and the other was an antiserum to formic acid‐denatured PHF (anti‐HFoPHF). Phosphorylated τ‐specific antibodies, anti‐ptau 1 and anti‐ptau 2, were prepared from anti‐PHF and anti‐HFoPHF, respectively. We found that both anti‐ptau 1 and anti‐ptau 2 labeled fetal or juvenile τ but not adult τ. The anti‐ptau 1‐ and anti‐ptau 2‐recognition sites were immunochemically localized to the fragment Asp³¹³ to Ile³²⁸ in the most COOH‐terminal portion of τ. Furthermore, Ser³¹⁵ was determined as the anti‐ptau 2 recognition site. The sequence surrounding Ser³¹⁵ was not found in the canonical sequences phosphorylated with known kinases.