Quences (Supplementary Figure 4e, Supplementary Figure 5a , and 6 and Supplementary Information 5). Previously published resolution NMR data have shown that the PGGG sequences in tau can adopt variety II -turns7, plus the 301PGGG304 sequence preceding 306VQIVYK311 is compatible together with the formation of a -hairpin. We illustrated the R2R3 306VQIVYK311-containing fragment derived from low energy expanded models developed by every process (Supplementary Figure 4c, d). The 306VQIVYK311-containing interface has the highest frequency of RI(dl)-2 Autophagy disease-associated mutations, particularly P301L and P301S (Fig. 1a). Other potential amyloid-forming regions, like the aggregation-prone 275VQIINK280 (Supplementary Figure 6), can also be preceded by 271PGGG274 and predicted to form a -hairpin (Supplementary Figure 4e and Supplementary Figure 5), nevertheless, it really is absent in current cryo-EM structures of tau aggregates3,43. Mapping identified missense mutations onto the ab Fenamic acid N-Phenylanthranilic acid initio -hairpin structure at the R2R3 interface (Supplementary Figure 4f), we hypothesized that this cluster of disease-associated mutations could destabilize the -hairpin secondary structure, therefore exposing the amyloid motif 306VQIVYK311 and enabling aggregation. This model is compatible with recent cryo-EM findings that indicate a disengagement of the 306VQIVYK311 N-terminal flanking sequence inside a fibril structure3. Hence, we focused our studies on the R2R3 motif of tau that includes 306VQIVYK311. P301L promotes extended types of tau. In silico modeling corroborated current biochemical findings16 and suggested a minimal sequence important to kind a collapsed structure around 306VQIVYK311. To understand how these structures could possibly self-assemble, we employed molecular dynamics (MD) simulations of two tau peptide fragments comprising the minimally structured fragment centered about the R2R3 interface (295DNIKHVPGGGSVQIVYK311): R2R3-WT and R2R3-P301L (Supplementary Table 2). To allow sufficient sampling of oligomer structures, we employed an unbiased algorithm determined by a lately created symmetry-constraint approach44. The trimer conformations obtained in simulations are depicted on a root mean square deviation (RMSD) matrix for both the R2R3-WT (Fig. 3a) and the R2R3-P301L mutant peptide fragments (Fig. 3b). For the R2R3-WT peptide fragment, we observe a dominant population of trimeric conformations composed of hairpins, whereas the P301L disease-associated mutation stabilizes an extended fibrillar kind. The energy basin for the R2R3-WT peptide fragment is predicted to be five kJmol lower inside a collapsed state than an extended state, whereas the R2R3-P301L peptide fragment is 3 kJmol lower in an extended state than a collapsed state (Fig. 3c and Supplementary Information six). Additionally, the free-energy surface suggests an energy barrier of five kJmolaRMSD matrix for wild kind 9 eight 7 6 Time (s) five 4 3 2 1 0b9 8 7 six Time (s) 5 4 three 2 1 0 1 two 0.7 RMSD (nm) three four five Time (s) 6 7 3.eight eight 9 0 1 two 0.7 3 four 5 Time (s) RMSD (nm) six 7 3.5 eight 9 RMSD matrix for P301L mutantc9 8CollapsedWild form P301LExtendedFree power (kJmol)6 5 4 3 2 1 0 0 0.2 0.four 0.6 0.eight 1 RMSD from hairpin (nm)Fig. 3 Wild-type and mutant peptides differentially populate collapsed and extended conformations. a Trimer conformations obtained from MD simulations of WT peptide fragment (R2R3-WT) together with the sequence 295DNIKHVPGGGSVQIVYK311. Two-dimensional root mean-squared-differences (RMSD’s) are calculated in between all pairs of conformations visited throughout MD simulations. Snapshots of trim.
