Abstract
Tau is an intrinsically disordered protein implicated in the pathogenesis of Alzheimer's disease and other neurodegenerative disorders. Here we describe the application of single-molecule Förster resonance energy transfer (smFRET) for the characterization of the interactions between tau and polyphosphate, an intracellular polymer that accelerates tau aggregation. We describe the design of tau constructs, purification and fluorescent labeling of tau, and details of acquisition and analysis of smFRET data. The protocols provided here outline an approach that may be applied to the study of other intrinsically disordered proteins and their binding partners.