Python scripts for global fitting of T1-edited DEER data used in "Deconvoluting monomer- and dimer-specific distance distributions between spin labels in a monomer/dimer mixture using T1-edited DEER spectroscopy" by T. Schmidt, N. Kubatova and G.M. Clore, J. Am. Chem. Soc. 2024, doi:10.1021/jacs.4c03916

Double electron-electron resonance (DEER) EPR is a powerful tool in structural biology, providing distances between pairs of spin labels. When the sample consists of a mixture of oligomeric species (e.g. monomer and dimer) the question arises as to how to assign the peaks in the DEER-derived probability distance distribution to the individual species. Here we propose incorporating an EPR longitudinal electron relaxation (<i>T</i>₁) inversion recovery experiment within a DEER pulse sequence to resolve this problem. The apparent <i>T</i>₁ between dipolar coupled electron spins measured from the inversion recovery time (t_inv) dependence of the peak intensities in the <i>T</i>₁-edited DEER-derived probability <i>P</i>(<i>r</i>) distance distribution will be affected by the number of nitroxide labels attached to the biomolecule of interest, for example, two for a monomer and four for a dimer. We show that global fitting of all the <i>T</i>₁-edited DEER echo curves, recorded over a range of inversion recovery times, permits the deconvolution of distances between spin labels originating from monomeric (longer <i>T</i>₁) and dimeric (shorter <i>T</i>₁) species. This is especially useful when the trapping of spin labels in different conformational states during freezing gives rise to complex <i>P</i>(<i>r</i>) distance distributions. The utility of this approach is demonstrated for two systems, the β₁ adrenergic receptor and a construct of the huntingtin exon-1 protein fused to the immunoglobulin domain of protein G, both of which exist in a monomer-dimer equilibrium.