Small angle X-ray scattering study of S100 proteins.

Small-angle X-ray scattering of both S100b and a mixture of S100a and S100ao (S100a,ao) was measured over a protein concentration range of 1.5 to 10.0 mg/ml. The addition of trifluoroperazine (TFP) to S100 solutions suppressed higher aggregation under the conditions studied. In the presence of TFP (1 mol TFP/mol of protein dimer), the radius of gyration of S100b and S100a,ao is found to be 19.5 +/- 0.3A and 20.2 +/- 0.3A, respectively, indicating that most S100 proteins may exist as dimers under the conditions studied. The observed difference (0.7 +/- 0.3A) in the radius of gyration between S100b and S100a,ao indicates that these dimers have different, asymmetrical shapes.