Fig. 4: Structural differences between Ub 11AcK and nonmodified Ub result in different binding affinities for the UBA domain of Ubiquilin-2.

a, c Weighted chemical shift perturbation (CSP, Δω) mapping obtained at the endpoint of the NMR titration experiment of Ub 11AcK (a) and nonmodified Ub (c) with the UBA domain of Ubiquilin-2 (UQ2-UBA) in approximately three times molar excess. Values exceeding the horizontal solid line are higher than the mean, and values exceeding the horizontal dashed line are higher than the mean plus one standard deviation. Background lines in gray highlight residues experiencing more than 90% decrease of signal intensity during the titration due to slow or intermediate exchange. Secondary structural elements are depicted on the top of the graph according to the NMR solution structure of nonmodified Ub (PDB ID 1D3Z)⁷⁹; the position of 11AcK is indicated by an arrow in a. b, d Individual binding isotherms are shown for the residues that were included into the global fitting procedure in order to determine the dissociation constant of the complex of UQ2-UBA with Ub 11AcK (b) and nonmodified Ub (d), with a concentration of Ub 11AcK and Ub of c = 33 µM. The corresponding K_d values are provided in the text and in Supplementary Fig. 5. Source data are provided as a Source Data file.