Fig. 4: Distance determination using measured FRET efficiencies, guided by FCG and homologous structures.

a Eight FRET pairs used to obtain the Förster Convolved with Gaussian (FCG) relation to determine the distance dependence of the FRET efficiency. The Cβ–Cβ distances were measured from the homology models based on human HCN1 (PDB:5U6P and PDB: 6UQF) assuming they correspond to the structures at 0 and −100 mV respectively (in the presence of cAMP). b The measured FRET efficiencies are plotted versus the distances measure in panel a (in R₀ units) as 4 black (0 mV) and 4 purple (−100 mV) circles. Predicted distance dependencies of the Förster equation (black) and the FCG relation (green) are shown. The FCG relation used a Gaussian distribution with a standard deviation, σ, of 5 Å (inset).