(A) Model-independent parameters of the SAXS analysis. Forward scattering intensity, I(0), in absolute units of cm−1. MWexp: Average MW of the oligomer as derived from the forward scattering and the protein concentration. The uncertainty of the MW determination is expected to be around 10% for the FP2, which was measured using the sample changer setup and around 20% for the SEC-SAXS-based setup. When taking this into account, the experimental MW values compare well with their nominal values, MWnom, calculated using a monomer MW of 55 kDa. Rg: Radius of gyration and Dmax: Maximal distance of the p(r). The I(0), Rg, and Dmax are derived from the indirect Fourier transformation as described in the Materials and methods section. (B–E) Experimental SAXS data (blue points), fit of rigid-body (RB) model (orange full line) and fit of Cn symmetric model with n = 2 (FP2), 3 (FP3), and 4 (FP4), respectively, in (C), (D), and (E) (green full line). Corresponding residual plots are presented underneath each SAXS plot. (F–G) Integrated SAXS intensity of the SEC-SAXS data obtained for FP3 and FP4. The frames used for the foreground (FP3/4 frames) and buffer frames selected for the background are indicated on the plots. (H) Direct comparison of the p(r) functions obtained from the SAXS data on FP1 E244K, FP2, FP3, and FP4.