Structural studies of different length Tau isoforms and disease-linked mutations

The microtubule-associated protein tau acts to stabilize and promote microtubule assembly primarily within the central nervous system, is present as one of six isoforms regulated by alternate genetic splicing and consists of an N-terminal projection domain and C-terminal assembly domain joined by a proline-rich region. Tau is the major component of both the neurofibrillary tangles in Alzheimer's disease and the paired-helical filaments characteristic of other diseases collectively termed tauopathies. Disease-causing mutations in tau have been identified from familial forms of one such tauopathy, frontotemporal dementia.;Here we study the effects of several of these mutations on the structural elements in the TauK19 fragment composed of the three microtubule-binding repeats found in all tau isoforms. We conducted sets of NMR experiments to obtain assignments for the mutant constructs both in solution and bound to membrane-mimetic SDS micelles. Secondary shift analysis shows that the mutations promote minor effects on previously reported helical propensities in both free and micelle-bound states. The E342V and K369I mutations in particular show changes within the proposed R4 helix and C-terminal tail respectively. NMR residual dipolar couplings support the helical nature of tau and suggest that K257T and E342V may increase fluctuations from helical to extended conformations. Titration with small unilamellar vesicles confirms tau-membrane associations and provides evidence that the R3 helix and filament nucleating PHF6 motif exhibit the earliest and strongest binding while the R3-R4 intrahelix region and the C-terminus remain unbound. One mutation, K257T, shows decreased local binding, while the E342V mutation may increase membrane affinity globally. Such effects on tau-membrane interactions could influence both normal function and pathological aggregation.;To facilitate future studies of full-length Tau isoforms we obtained assignments for the shortest and longest isoforms: Tau352 and Tau441. Low dispersion and spectra overlap necessitated the use of recent advances in reduced-dimensionality NMR. We collected sets of G-matrix fourier transform NMR experiments for Tau352 and Tau441, obtaining 97% and 92% backbone resonance assignments respectively. Chemical shift analysis of this data shows good agreement with previous studies and reinforces the presence of helical propensity in the assembly domain of tau.