C-H ... π interplay between Ile308 and Tyr310 residues in the third repeat of microtubule binding domain is indispensable for self-assembly of three- and four-repeat tau.

Information on the structural scaffold for tau aggregation is important in developing a method of preventing Alzheimer's disease (AD). Tau contains a microtubule binding domain (MBD) consisting of three or four repeats of 31 and 32 similar residues in its C-terminal half. Although the key event in tau aggregation has been considered to be the formation of β-sheet structures from a short hexapeptide (306)VQIVYK(311) in the third repeat of MBD, its aggregation pathway to filament formation differs between the three- and four-repeated MBDs, owing to the intermolecular and intramolecular disulphide bond formations, respectively. Therefore, the elucidation of a common structural element necessary for the self-assembly of three-/four-repeated full-length tau is an important research subject. Expanding the previous results on the aggregation mechanism of MBD, in this paper, we report that the C-H … π interaction between the Ile308 and Tyr310 side chains in the third repeat of MBD is indispensable for the self-assembly of three-/four-repeated full-length tau, where the interaction provides a conformational seed for triggering the molecular association. On the basis of the aggregation behaviours of a series of MBD and full-length tau mutants, a possible self-association model of tau is proposed and the relationship between the aggregation form (filament or granule) and the association pathway is discussed.