FTD-tau S320F mutation stabilizes local structure and allosterically promotes amyloid motif-dependent aggregation

Abstract

Amyloid deposition of the microtubule-associated protein tau is associated with neurodegenerative diseases. In frontotemporal dementia with abnormal tau (FTD-tau), missense mutations in tau enhance its aggregation propensity. Here we describe the structural mechanism for how an FTD-tau S320F mutation drives spontaneous aggregation, integrating data from in vitro, in silico and cellular experiments. We find that S320F stabilizes a local hydrophobic cluster which allosterically exposes the 306VQIVYK311 amyloid motif; identify a suppressor mutation that destabilizes S320F-based hydrophobic clustering reversing the phenotype in vitro and in cells; and computationally engineer spontaneously aggregating tau sequences through optimizing nonpolar clusters surrounding the S320 position. We uncover a mechanism for regulating tau aggregation which balances local nonpolar contacts with long-range interactions that sequester amyloid motifs. Understanding this process may permit control of tau aggregation into structural polymorphs to aid the design of reagents targeting disease-specific tau conformations.

Role of G326 in Determining the Aggregation Propensity of R3 Tau Repeat: Insights from Studies on R1R3 Tau Construct

“…The influence of the NH6 peptide of R2 repeat ( 295 DNIKHV 300 ) on the conformational properties of R3 was observed previously by Chen et al 53 Therefore, the sequence-dependent modulation provides insights into the conformational diversity offered by NH6 peptides, in line with the role of VQ6 peptides. 53,66 The involvement of R1 repeat in aggregation supports its part in promoting fibril formation, as recently demonstrated in our laboratory. 50 Results from NMR experiments that probed backbone conformations, such as average amide chemical shift differences and secondary structure propensities, reveal that the residues of the AIM are perturbed due to the G326E mutation.…”

“…Protocols for obtaining initial conformations and simulations are discussed in materials and methods. 53 Three replicates of 2 μs simulations were carried out for each construct, accounting for a total simulation time of 12 μs (3 replicates x 2 μs x 2 constructs). Inter-residue C α −C α contact frequencies of the trajectories are plotted to obtain insights regarding the transient long-range interactions (Figure 5C,D).…”

“…The simulation methods and protocol followed for preparing the starting structure are discussed elsewhere. 53 The starting structures were obtained by performing unrestrained MD with random coil starting structures modeled by using the fab command in the Pymol molecular graphics package. Dodecahedral boxes were chosen to perform the simulations with a distance spacing of 1.4 nm between the center of the random-coil peptide and the edges of the box.…”

Disease associated mutations in tau encode for changes in aggregate structure conformation

“…Although there have been previous studies of structural differences induced by a small subset of mutations in short synthetic constructs of tau 52,53 , comparison of the effects of a broad set of tau mutations in the context of full-length tau has not been characterized. Thus, to investigate the role of disease-associated tau missense mutations in modulating tau aggregate structure, we generated a panel of 37 tau variants (WT and 36 missense mutants) for systematic comparison of their properties.…”

Disease-Associated Mutations in Tau Encode for Changes in Aggregate Structure Conformation

“…Although there have been previous studies of structural differences induced by a small subset of mutations in short synthetic constructs of tau, , comparison of the effects of a broad set of tau mutations in the context of full-length tau has not been characterized. One of the hurdles to this goal is the development of high-throughput methods for the production of tau variants and comparisons of their relative structures.…”