Fluorescence fluctuations of quantum-dot sensors capture intracellular protein interaction dynamics

We extend the in vitro principle of co-immunoprecipitation to quantify dynamic protein interactions in living cells. using a multiresolution implementation of fluorescence correlation spectroscopy to achieve maximal temporal resolution, we monitored the interactions of endogenous bait proteins, recruited by quantum dots, with fluorescently tagged prey. With this approach, we analyzed the rapid physiological regulation of protein kinase A.