Distance distributions from individual fits to the DEER data for Pgp in Fig. 6. (A) The model-free P(R) were obtained using Tikhonov regularization in DeerAnalysis 2019 (Jeschke et al., 2006). The optimal regularization factor was determined by generalized cross-validation and the starting time point for background fitting using the validation tool. (B) The model-based P(R) were obtained assuming a 3-D exponential background and using Gaussian components in DD (Brandon et al., 2012; Stein et al., 2015; Hustedt et al., 2018). The optimal number of Gaussians, n, was determined using BIC values.