Many protein structures can be characterized with small angle X-ray (SAXS). SAXS differs from X-ray crystallography in that it is applied to proteins in solution rather than crystals; thus, it can be applied to a much wider range of proteins in states more closely resembling their functional forms than X-ray crystallography. Because the sample is in solution, the SAXS information is rotationally averaged and so the resulting SAXS profile gives less structural information than X-ray crystallography; however, this is often sufficient to determine problems with the structure or to distinguish possible conformations.

IMP includes a command line tool foxs for handling SAXS profiles, as well as a web interface, which functions similarly. See the FoXS tutorial for a demonstration.