Protein-protein interactions in solution and their interplay with protein specific functions

We summarize recent developments of our small angle scattering studies on protein-protein interactions in solution. We have been focusing especially on representative proteins that function at exceptionally high concentration in human body, whose collective nature, rather than a specialized function of an isolated single molecule, plays an important role for their specific biological functions; for instance, human serum albumin (HSA), actin, and human hemoglobin (Hb). We use a static structure factor analysis, which offers information about spatial distributions of the proteins, as well as a Fourier inversion technique for the form factor, giving a real-space picture of the protein assemblies.