The influence of fluorescent protein maturation on FRET measurements in living cells

Förster resonance energy transfer (FRET)-based sensors are a valuable tool to quantify cell biology, yet identifying and preventing potential artifacts are needed to exploit their full potential. We show here that artifacts arising from slow donor mCerulean3 maturation can be substantially diminished by constitutive expression both in prokaryotic and eukaryotic cells, which can also be achieved by incorporation of faster maturing FRET donors. We developed an improved version of the donor mTurquoise2, which matures faster than the parental protein. Our analysis shows that using equal maturing fluorophores in FRET-based sensors or using constitutive low expression conditions helps to reduce maturation-induced artifacts, without the need of additional noise-inducing spectral corrections. In general, we show that monitoring and controlling the maturation of fluorescent proteins in living cells is important and should be addressed in in vivo applications of genetically-encoded FRET sensors.