protein (MAP) tau is abnormally hyperphosphorylated in Alzheimer disease
and accumulates in neurons undergoing neurofibrillary degeneration. In
the present study, the
associations of the Alzheimer-hyperphosphorylated tau (AD P-tau) with the high molecular weight MAPs (HMW-MAPs) MAP1 and MAP2 were investigated. The AD P-tau was found to aggregate with MAP1 and MAP2 in solution. The association of AD P-tau to the MAPs resulted in inhibition of MAP-promoted microtubule assembly. However, unlike the coaggregation of AD P-tau and normal tau, the association between AD P-tau and the HMW-MAPs did not result in the formation of filaments/ tangles. The affinity of the tau-AD P-tau association was higher than that of HMW-MAPs-AD P-tau because normal tau inhibited the latter binding. The association between AD P-tau and the HMW-MAPs also appeared to occur in situ because these proteins cosedimented from the Alzheimer brain extracts, and, in the sediment, the levels of the HMW-MAPs correlated with the levels of AD P-tau. These studies suggested that the abnormally phosphorylated tau can sequester both normal tau and HMW-MAPs and disassemble microtubules but, under physiological conditions, can
form tangles of filaments only from tau.