Insights into the conformations and dynamics of intrinsically disordered proteins using single-molecule fluorescence.

Most proteins are not static structures, but many of them are found in a dynamic state, exchanging conformations on various time scales as a key aspect of their biological function. An entire spectrum of structural disorder exists in proteins and obtaining a satisfactory quantitative description of these states remains a challenge. Single-molecule fluorescence spectroscopy techniques are uniquely suited for this task, by measuring conformations without ensemble averaging and kinetics without interference from asynchronous processes. In this paper we review some of the recent successes in applying single-molecule fluorescence to different disordered protein systems, including interactions with their cellular targets and self-aggregation processes. We also discuss the implementation of computational methods and polymer physics models that are essential for inferring global dimension parameters for these proteins from smFRET data. Regarding future directions; 3- or 4-color FRET methods can provide multiple distances within a disordered ensemble simultaneously. In addition, integrating complementary experimental data from smFRET, NMR and SAXS will provide meaningful constraints for molecular simulations and will lead to more accurate structural representations of disordered proteins. This article is part of a Special Issue entitled: Biophysics in Canada, edited by Lewis Kay, John Baenziger, Albert Berghuis and Peter Tieleman.