Single-molecule FRET studies of ion channels.

Different types of fluorescence spectroscopy approaches have over the last two decades become important techniques in studies of ion channel structure and dynamics. Many fluorescence methods have been used to examine a huge variety of ion channels. Any fluorescence study of ion channels requires the presence of fluorophores, which may be intrinsic to the channel protein, attached either extrinsically to the protein, or be simply located nearby the channel to monitor local conditions such as for many of the ion-sensitive dyes. Many ion channel studies utilize protein-bound or intrinsic protein fluorophores. Single-molecule Förster resonance energy transfer (smFRET) spectroscopy has been particularly useful in gaining detailed structural information for multimeric membrane proteins including ion channels. This technique presents a major advancement in studies of structural dynamics of these membrane proteins. Although it has required different approaches to protein labelling, control of the protein state, as well as careful analysis of the orientations, geometries, and number of fluorescent probes, the smFRET methodology provides an excellent tool for studying the structure of ion channels.