Probing IDP Interactions with Membranes by Fluorescence Spectroscopy.

The microtubule-associated protein tau has been extensively studied as a culprit in Alzheimer's disease and other neurodegenerative diseases known as tauopathies. Challenges in structurally defining tau protein emerge from its disordered nature, which makes it difficult to crystallize, and hinder efforts to interpret tau protein's true function. The complexity of intrinsically disordered proteins (IDPs) necessitates a multifaceted approach to study their interactions including multiple spectroscopic methods that can report on local protein environment and structure at individual residue positions. We and others have shown that in addition to binding to microtubules, tau binds to lipid membranes. Tau-membrane interactions may be relevant both to normal tau function and to tau aggregation and pathology. Here we describe the use of fluorescence spectroscopy as a probe of protein-membrane interactions to determine whether there is an interaction, which residues participate, and the extent/nature of the interface between the protein and the membrane. We provide a protocol for how the membrane interactions of tau protein, as an example, can be probed by fluorescence spectroscopy, including details of how the samples should be prepared and guidelines on how to interpret the results.