A genetically encoded small-size fluorescent pair reveals allosteric conformational changes of G proteins upon its interaction with GPCRs by fluorescence lifetime based FRET.

The dynamics of GPCRs (G protein-coupled receptors) coupling for cognate G proteins play a critical role in signal transduction. Herein, we reported a site-specifically labelled small-sized fluorescent pair 7-HC/FlAsH ((7-hydroxycoumarin-4-yl)-ethylglycine/fluorescein arsenical hairpin) for fluorescence lifetime based FRET (fluorescence resonance energy transfer) to reveal conformational differences of G alpha(i1)(inhibitory G proteins) and G alpha(s)(stimulatory G proteins) upon beta(2)AR (beta(2)-adrenergic receptor) coupling. It offers a new generally applicable method to probe protein dynamic interactions or conformational changes.