Figure 3.

FRET data for wild-type FGFR3 and the A391 mutant constructs as a function of acceptor concentration. Each of the ∼1000 data points represents a single vesicle for which the FRET efficiency, donor concentration, and acceptor concentration are determined using the quantitative-imaging FRET method. Black solid squares and red open circles indicate the FRET efficiencies measured for the wild-type and mutant constructs, respectively. Data scatter in this type of experiment is due to random noise in image acquisition, and is reducible by collecting a large number of data points (36). The solid line shows the so-called called random FRET, which occurs if there are no specific interactions between the membrane proteins; this phenomenon is well described by the model of Wolber and Hudson (40).