where FD and FA denote donor and acceptor fluorescence intensities after donor excitation, respectively, that were corrected for background signal, donor leakage (D = 0.13) and acceptor direct excitation (A = 0.05) contributions. The γ-factor (γ = 1.2) was used to account for differences in brightness and detection efficiency for the donor and acceptor fluorophores. The correction factors were determined for all samples and a single average value of those was used for correcting the transfer efficiencies for all datasets.