D Plot of 15N-labeled UBE2SUBC WT and ER/ER 1H linewidth changes in the presence of Ub revealing the ER/ER variant has a more dynamic active-site cysteine and HTH, but a more stabilized crossover helix, indicative of the "closed" state. Shown are the best-fit values and standard deviations (SD) estimated from the covariance matrix analysis of NMR spectra with n = 2048 measurement points for 16 ppm in the 1H dimension. 