[7] Structure and interactions of proteins in solution studied by small-angle neutron scattering

Publisher Summary The use of the small-angle neutron scattering (SANS) technique as an analytical tool for the study of global structures of macromolecules in solution follows naturally from the earlier development of the small-angle X-ray scattering (SAXS) technique. This chapter presents the method of SANS as applied to soluble globular proteins in solution. Its advantages over the SAXS technique are also brought out in the discussion. The emphasis is put on analysis of scattering data from systems at both low and moderately high concentrations, which better simulate physiological conditions. Owing to the considerable number of charges on proteins in solution at pH 7, there exists a long range electrostatic interaction between the molecules even at the 1% (g/dl) concentration level. It should be emphasized that the dilute regime where interactions can be neglected is an impractical regime in which to perform experiments because of the severe loss in scattered intensity for solutions with less than 0.1% protein. For globular proteins with known conformation, experiments performed at high concentrations provide additional information, such as the effective surface charge, the amount of bound water, and the local spatial ordering of the molecules in solution.