SAXS experiments were performed on P1–304N1–525 complexes purified, as described above. Samples were adjusted to three different concentrations between 0.25 and 3.5 mg/ml and were measured at 20°C on the BM29 beamline at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. Scattering was recorded at a wavelength of 0.992 Å, and samples were exposed 10 times for 2 s. All frames were analyzed for radiation damage and excluded if necessary. All other frames of sample and buffer were averaged respectively, and buffer scattering curves were subtracted from the scattering curves of the samples.