Application of single molecule Förster resonance energy transfer to protein folding.

Protein folding is a process characterized by a large degree of conformational heterogeneity. In such cases, classical experimental methods yield only mean values, averaged over large ensembles of molecules. The microscopic distributions of conformations, trajectories, or sequences of events often remain unknown, and with them the underlying molecular mechanisms. Signal averaging can be avoided by observing individual molecules. A particularly versatile method is highly sensitive fluorescence detection. In combination with Förster resonance energy transfer, distances and conformational dynamics can be investigated in single molecules. This chapter introduces the practical aspects of applying this method to protein folding.