Fig. 2

Interaction between Ubl45 and CD identified in solution using NMR. a The peak dispersion and resolution in the ¹H–¹⁵N correlation spectrum of Ubl45 (45 µM; 25 kDa; coloured blue) indicates a well-folded protein. Assignments are indicated, those for the crowded regions, indicated in grey, are shown in Supplementary Figure 1a. b The addition of 450 µM CD prompted very little chemical shift perturbations (CSPs). The biggest observed CSP of 0.019 ppm for Y1093 is illustrated in this zoom. c Upon titration of CD the peaks in the Ubl45 spectrum shows significant decrease in intensity. Here the intensity ratios between the apo spectrum (1:0) and the highest titration (1:10) are plotted against the residue numbers. The average is indicated by a dotted line, while residues that were found in the crystal structure to interact (d) are highlighted in the bar graph. d Structure and intermolecular interface in the Ubl45-CDUb structure (PDB: 5JTV³⁶), showing contacts between both the tail and the core of Ubl45 to CD. Ubl45 residues that are within 4 Å of CD are shown as sticks and indicated. e The same intensity plot as in c, but now done for the titration with CDUb indicates that the tail now does get immobilised. For c and e, the bars are normalised against the overall intensity of all peaks of the apo spectrum