SUFU contains an intrinsically disordered region. (a, b) Trypsin digest analysis of MBP-SUFU-FL. Open green rectangles indicate structured parts of the protein in our crystallographic model. The red rectangles FR1–FR5 represent proteolytic fragments. (c, d) Fit of MBP-SUFU-FL and MBP-SUFU-Δ crystal structures into average ab initio envelopes calculated from SAXS data. MBP, blue; SUFU N-terminal domain, beige; SUFU C-terminal domain, green. Residues of the IDR, built by CORAL, are shown in black. Peptides that are more protected from HDX in MBP-SUFU-FL than in MBP-SUFU-Δ are shown in pink.