Exploring the Functional and Structural Impact of Disease-Associated Mutants of Tau

Abstract

Tau is an intrinsically disordered microtubule associated protein, whose pathological self-association is linked to several tauopathies, including Alzheimer's disease. A number of lines of evidence support tau aggregation as well as loss of its native interactions with microtubules (MTs) as contributing to pathology. Prior work from our lab showed that both disease-relevant as well as designed point mutations to tau's microtubule binding region (MTBR) enhance binding of tau to soluble tubulin. This observation indicates the mechanism of MT destabilization in disease may arise, in part, from an altered distribution of tubulin- and microtubule-bound tau. Here we determine whether the increase in affinity observed previously generally holds for disease-relevant tau mutants. Specifically, we characterize variants within all four repeats in the MTBR and at both N- (R5L and R5H) and C-termini (R406W). To investigate this, we used fluorescence correlation spectroscopy (FCS) to quantify the binding of tau variants to soluble tubulin. Changes in the affinity and function were correlated with the topological features of each tau mutant in solution or upon interaction with soluble tubulin by using single-molecule FRET. Together, our work allows to identify domain/region specific conformational changes in tau relevant to tauopathies and to explore the effect on its intrinsically disordered features. This provides a structural basis for understanding the impact of tau disease mutations in the tau-tubulin complex.