All SAXS data collection was performed at the SIBYLS beamline, an international user facility. An application for experiments is accessible at www.bl1231.als.lbl.gov . The data collection strategy has been designed to minimize errors due to instrumentation, radiation damage and concentration dependant phenomenon. The strategy applied depended on available stock concentration and size of the protein. SAXS data were collected on 3 serial dilutions of each sample preparation starting at a maximum 10 and a minimum of 1 mg/ml. Sample loading for data collection for each protein proceeded in the following order, lowest concentration, middle concentration, highest concentration followed by a final buffer measurement. The sample cell was washed between protein solutions using a mild detergent soak for 1 minute followed by 3 rinses with buffer solution. The subtraction of buffer collected before the sample was compared to buffer collected after each sample to insure the subtraction process was not subject to instrument variations. Data was collected from two short and one long X-ray exposure for each protein sample. The short exposures were compared against one another to identify whether significant radiation damage occurred on this time scale. The beam size at the sample is 4×1mm and converges at the detector to a 100×100µm spot. The large beam size at the sample spreads radiation over the entire sample greatly reducing radiation damage. Concentrations were compared against one another to determine whether concentration dependant structure factors contributed to the data. In two cases minor concentration dependence was observed and corrected by extrapolating behavior to zero concentration9 using code developed in house. A final scattering curve used for analysis was created for each sample (Supplementary Figure 2 ).
For most samples only 1 Å X-rays were used. Short exposures were 0.5 seconds while the long exposures were 5 seconds. However for proteins with long dimensions such as PF1548, 1.5 Å wavelength was also used to better define the maximum distances. Short and long exposures were 4 and 40 seconds respectively. All data were collected at room temperature.
For most samples only 1 Å X-rays were used. Short exposures were 0.5 seconds while the long exposures were 5 seconds. However for proteins with long dimensions such as PF1548, 1.5 Å wavelength was also used to better define the maximum distances. Short and long exposures were 4 and 40 seconds respectively. All data were collected at room temperature.