Figure 3: Allosteric effect of SUMO1_1–92 on the catalytic channel as detected by CSP and CPMG-relaxation dispersion.

(a) Stereo view of SENP1 structure coloured according to CSP (calculated as) caused by formation of the complex with SUMO1_1–92. The gradient from white to red corresponds to the CSP (from small to large) of backbone NH groups. Above average CSP (0.05 p.p.m.) of the methyl groups are indicated by magenta ball and stick figures. (b) Stereo view of SENP1 structure coloured according to the R_ex values extracted from the fitted CPMG-relaxation dispersion profiles of the SENP1:SUMO1_1–92 complex at molar ratio of 1:0.2. The gradient from white to red corresponds to the R_ex (from small to large). Substantial methyl CPMG-relaxation dispersion is indicated by magenta ball and stick figures. In both a and b, key residues at the catalytic channel are shown with their side chains and labelled. SUMO1_1–92 is shown in cyan, and the C-terminal segment in SUMO1-FL is shown in yellow on the crystal structure of the complex between SUMO1-FL and SENP1 (PDB: 2IY1). (c,d) Comparison of R_ex extracted from CPMG-relaxation dispersion between free SENP1 and SENP1 in complex with a 0.2 molar equivalence of SUMO1_1–92 detected by ¹⁵N-CPMG dispersion (c) and ¹³C-methyl-CPMG dispersion (d). Residues at the direct binding surface for the β-grasp domain (defined as the buried surface by SUMO1_1–92 as provided by the Interface Residues script, http://www.pymolwiki.org/index.php/InterfaceResidues, of the software pymol) are indicated in black, at the catalytic centre in red (defined as contacting the residues 96–98 of SUMO1-FL), and at neither the catalytic centre nor the direct binding surface in green. (e) Representative CPMG dispersion profiles of the resonances of SENP1 residues at 600 (circle) and 700 (square) MHz NMR instruments when free and partially bound to SUMO1_1–92. Error bars were obtained from duplicated measurements.