Fig. 3: The C-terminal dimer distance of CH₂COCF₃ PASc observed by CODEX dephasing for both bound (yellow) and free (blue) states of CitApc.

At the mixing time of 250 ms, the bound state CODEX signal decays to 0.65 of the reference experiment (A, inset yellow); the decay rate fits to an inter- CF₃ distance of 13.6 \(\pm\) 3.0 Å, with the exponential decay fit curve of \(0.5*{{{\rm{e}}}}^{-0.0053*{{\rm{t}}}}-0.5\), matching the expected inter-dimer distance at the C-terminus of the parallel dimer (C). In contrast, the free state CODEX signal is almost the same as the reference experiment (A, inset blue) through all mixing times, corresponding to a large inter dimer distance at the C-terminus of more than 20 Å, agreeing with the anti-parallel dimer (B). Example CODEX decay curves at different inter fluorine distances are shown (A, gray). 30% of the bound state CitApc protein present in the citrate free sample caused the minor CODEX decay. Error (taken at 1 SD), signal and noise levels of each individual measurements are recorded in Supplementary Tables 11 and 12. The CODEX decay curve could be acquired beyond the ¹⁹F T₁ of 321 ms (Supplementary Fig. 14), thanks to an eight-fold DNP signal enhancement (Supplementary Fig. 11B).