Fig. 1: Design and characterization of CRBN^midi.

a Domain composition of full-length CRBN (top), constructs previously used for structural and biophysical characterization, CRBN^ΔN and CRBN^TBD, and constructs 1–15 designed in this study. The most promising construct 8 was designated as CRBN^midi. Mutated residues are indicated as blue lines. b Ni-NTA affinity pull-down assay of lysates from E. coli BL21(DE3) cells expressing candidate constructs 1–15 with an N-terminal His₆ (H) or His₆-MBP (M) tag. The expected size of each construct is marked with a yellow arrow. The experiment was performed as one replicate. Uncropped gels are provided as a Source Data file. c Crystal structure of CRBN^midi in the apo state, containing Lon (yellow), HB (orange) and TBD (red) domains. The mutated residues are indicated (blue), the unresolved region containing the GSG linker is shown as blue dashed line, and Zn²⁺ is shown as a purple sphere. d Superposition of apo CRBN^midi (yellow, orange, red) with CRBN^ΔN:DDB1 bound to lenalidomide (grey, PDB ID: 4TZ4¹⁰). DDB1 is shown as a grey surface.