FRET-Based Biosensors: Genetically Encoded Tools to Track Kinase Activity in Living Cells

Fluorescence microscopy is widely used in biology to localize, to track, or to quantify proteins in single cells. However, following particular events in living cells with good spatio-temporal resolution is much more complex. In this context, Forster resonance energy transfer (FRET) biosensors are tools that have been developed to monitor various events such as dimerization, cleavage, elasticity, or the activation state of a protein. In particular, genetically encoded FRET biosensors are strong tools to study mechanisms of activation and activity of a large panel of kinases in living cells. Their principles are based on a conformational change of a genetically encoded probe that modulates the distance between a pair of fluorescent proteins leading to FRET variations. Recent advances in fluorescence microscopy such as fluorescence lifetime imaging microscopy (FLIM) have made the quantification of FRET efficiency easier. This review aims to address the different kinase biosensors that have been developed, how they allow specific tracking of the activity or activation of a kinase, and to give an overview of the future challenging methods to simultaneously track several biosensors in the same system