Genetically Encoded FRET-Based Tension Sensors.

Genetically encoded Förster resonance energy transfer (FRET)-based tension sensors measure piconewton-scale forces across individual molecules in living cells or whole organisms. These biosensors show comparably high FRET efficiencies in the absence of tension, but FRET quickly decreases when forces are applied. In this article, we describe how such biosensors can be generated for a specific protein of interest, and we discuss controls to confirm that the observed differences in FRET efficiency reflect changes in molecular tension. These FRET efficiency changes can be related to mechanical forces as the FRET-force relationship of the employed tension sensor modules are calibrated. We provide information on construct generation, expression in cells, and image acquisition using live-cell fluorescence lifetime imaging microscopy (FLIM). Moreover, we describe how to analyze, statistically evaluate, and interpret the resulting data sets. Together, these protocols should enable the reader to plan, execute, and interpret FRET-based tension sensor experiments. © 2019 by John Wiley & Sons, Inc.