The state of phosphorylation of normal adult brain tau, fetal tau, and tau from Alzheimer paired helical filaments at amino acid residue Ser(262)

Antibody Ab262 was raised against a synthetic tau peptide (SKIGSTENLK, amino acids 258-267 of tau, termed Ser(262) peptide). The antibody was more reactive with Ser(262) peptide and unphosphorylated tau than a related phosphopeptide [SKIGS(P)TENLK, termed P-Ser(262) peptide] and tau phosphorylated by a partially purified kinase, glycogen synthase kinase (GSK) 3 beta. Ab262 reacted poorly with a peptide having the sequence DRV-QSKIGSLD (amino acids 348-358). Treatment of P-Ser(262) peptide or GSK 3 beta phosphorylated tau with alkaline phosphatase increased Ab262 immunoreactivity, indicating that Ab262 is a reagent useful for studying tau phosphorylation at the Ser(262) residue. The Ab262 immunoreactivity was detected in tau from normal brains and Alzheimer paired helical filament (PHF-tau) and in PHFs. Alkaline phosphatase treatment had no effect on the Ab262 immunoreactivity of normal tau and PHF-tau but altered the Tau-1 and PHF-1 immunoreactivities. tau proteins from rat brains at 3 and 8 h postmortem exhibited 5 and 19%, respectively, more Ab262 immunoreactivity than tau from fresh tissues. In comparison, rat tau at 8 h postmortem was 40% more immunoreactive with Tau-1. The results suggest that Ser(262) is not a major phosphorylation site in vivo. Moreover, there is little or no difference between PHF-tau and normal tau in the extent of phosphorylation at Ser(262).