Mutations in the tau gene are known to cosegregate with the disease in frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). However, the molecular mechanism by which these mutations might lead to the disease is not understood. Here, we show that four of the FTDP-17 tau mutations, R406W, V337M, G272V, and P301L, result in tau proteins that are more favorable substrates for phosphorylation by brain protein kinases than the wild-type, largest four-repeat protein 4L and 4L more than 3L. In general, at all the sites studied, mutant tau proteins were phosphorylated faster and to a higher extent than 4L and 4L > 3L. The most dramatic difference found was in the rate and level of phosphorylation of 4L R406W at positions Ser-396, Ser-400, Thr-403, and Ser-404. Phosphorylation of this mutant tau was 12 times faster and 400% greater at Ser-396 and less than 30% at Ser-400, Thr-403, and Ser-404 than phosphorylation of 4L. The mutated tau proteins polymerized into filaments when 4 -6 mol of phosphate per mol of tau were incorporated, whereas wild-type tau required ϳ10 mol of phosphate per mol of protein to self-assemble. Mutated and wild-type tau proteins were able to sequester normal tau upon incorporation of ϳ4 mol of phosphate per mol of protein, which was achieved at as early as 30 min of phosphorylation in the case of mutant tau proteins. These findings taken together suggest that the mutations in tau might cause neurodegeneration by making the protein a more favorable substrate for hyperphosphorylation.

At present, the conformation-dependent monoclonal antibodies (mAb) provide the only information on folding of tau in the core PHF. Monoclonal antibody MN423 recognizes all and only those Alzheimer's disease (AD) core paired helical filaments (PHFs) subunits, which terminate at Glu391. Using recombinant analogs of the core PHF subunit corresponding to tau residues s297-391, we found that the C-terminal pentapeptide 387 DHGAE 391 represented only one component of the structure recognized by mAb 423. Therefore, deletion mutants of the core subunit were generated to identify assembled parts of this conformational structure. We localized two spatially close components in the region [306][307][308][309][310][311][312][313][314][315][316][317][318][319][320][321][322][323][324][325]

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Tau protein is an intrinsically disordered protein. Its physiological state is best described as a conformational ensemble (CE) of metastable structures interconverting on the local and molecular scale. The monoclonal antibody DC39C recognizes a linear C‐terminal tau epitope, and as the tau interaction partner, its binding parameters report about tau CE. Association kinetics of DC39C binding, together with crosslinking mass spectrometry, show differences in the accessibility of the C terminus in CEs of tau isoforms. Furthermore, removal of the C terminus accelerated the aggregation kinetics of three‐repeat tau proteins. Our results suggest a novel mechanism of splicing‐driven regulation of the tau C‐terminal domain with consequences on the specific roles of tau isoforms in microtubule assembly and pathological aggregation.

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