Phosphorylation-mimicking glutamate clusters in the proline-rich region are sufficient to simulate the functional deficiencies of hyperphosphorylatedtau protein

The microtubule-associated tau proteins represent a family of closely relat ed phosphoproteins that become enriched in the axons during brain developme nt. In Alzheimer's disease (AD), tau aggregates somatodendritically in pair ed helical filaments in a hyperphosphorylated form. Most of the sites that are phosphorylated to a high extent in paired helical filament tau are clus tered in the proline-rich region (P-region; residues 172-251) and the C-ter minal tail region (C-region; residues 368-441) that flank tau's microtubule -binding repeats. This might point to a role of a region-specific phosphory lation cluster for the pathogenesis of AD. To determine the functional cons equences of such modifications, mutated tau proteins were produced in which a P- or C-region-specific phosphorylation cluster was simulated by replace ment of serine/threonine residues with glutamate. We show that a phosphoryl ation-mimicking glutamate cluster in the P-region is sufficient to block mi crotubule assembly and to inhibit tau's interaction with the dominant brain phosphatase protein phosphatase 2A isoform AB alphaC. P-region-specific mu tations also decrease tau aggregation into filaments and decrease tau's pro cess-inducing activity in a cellular transfection model. In contrast, a pho sphorylation-mimicking glutamate cluster in the C-region is neutral with re gard to these activities. A glutamate cluster in both the P- and C-regions induces the formation of SDS-resistant conformational domains in tau and su ppresses tau's interaction with the neural membrane cortex. The results ind icate that modifications in the proline-rich region are sufficient to induc e the functional deficiencies of tau that have been observed in AD. They su ggest that phosphorylation of the proline-rich region has a crucial role in mediating tau-related changes during disease.