LAUSR

Solution small-angle neutron scattering (SANS) combined with contrast variation provides information about the size and shape of individual components of a multi-component biological assembly, as well as the spatial arrangements between the components. The large difference in the neutron scattering properties between hydrogen and deuterium is key to the method. Isotopic substitution of deuterium for some or all of the hydrogen in either the molecule or the solvent can greatly alter the scattering properties of the biological assembly, often with little or no change to its biochemical properties. Thus, SANS with contrast variation provides unique information not easily obtained using other experimental techniques.If used correctly, SANS with contrast variation is a powerful tool for determining the solution structure of multi-component biological assemblies. This chapter discusses the principles of SANS theory that are important for contrast variation, essential considerations for experiment design and execution, and the proper approach to data analysis and structure modeling. As sample quality is extremely important for a successful contrast variation experiment, sample issues that can affect the outcome of the experiment are discussed as well as procedures used to verify the sample quality. The described methodology is focused on two-component biological complexes. However, examples of its use for multi-component assemblies are also discussed.