Extended Data Fig. 3: Structural and biophysical characterisation of TRIM21.

a, Schematic of TRIM21 protein sequence indicating RING, B Box, coiled-coil and PRYSPRY domain boundaries. b, SEC-MALS chromatograms of T21CC235 loaded at concentrations of 15 (black), 5 (green), 0.55 (blue) and 0.25 mg/ml (red) in which the refractive index is indicated by the solid lines while the molar mass evaluated from the light scattering analysis is indicated with the corresponding coloured dotted lines. c, Isothermal titration calorimetry (ITC) trace of T21CC235 fitted to a dimer dissociation model reveal an enthalpy of 65 kcal/mol and Kd of 7 µM. d, Analytical ultracentrifugation (AUC) sedimentation velocity analysis of T21RBCC in solution. The upper panel shows absorbance profiles with best fits of a c(s) model (coloured lines) and their residuals to the fits underneath. The different colours represent scans at different times: blue is the earliest time points where very little material has sedimented; through to red where all the material has sedimented and the signal is near baseline across the radius. The lower panel shows the c(s) distribution of specie. T21RBCC sedimented with coefficient of 2.5–2.6S (S_w,20 = 3.3–3.6S) with a frictional ratio of 1.49–1.52 corresponding to a mass of between 52–55 kDa, close to that expected for a dimeric species. e, Concentration-normalised scattering plots and DAM fits from SAXS data for T21CC235 (cyan, χ = 1.00), MBP-T21CC235 (green, χ = 1.31) and T21RBCC (purple, χ = 1.05). f, The linear Guinier regions from (e). f, Derived P(r) curves. The CC235 P(r) curve is consistent with an elongated rod, while the two peaks observed for MBP-T21CC235 and T21RBCC are consistent with dumbbell-shaped molecules. h, Scattering plot with DAM fit from TRIM21:Fc SAXS data (red line, 1.00), TRIM21:Fc atomic model fit (blue, χ = 1.04), and apo-TRIM21 atomic model fit (brown dashed,, χ = 2.00). i, The linear Guinier regions from (h). j, Derived P(r) curves.