IgG antibody represents one-third of new drugs currently in development. We will unravel the solution structures of the Fab and Fc fragments within IgG. Following our earlier solution structures for IgG, IgA and other human antibodies, we will apply our powerful constrained modelling approach based on neutron and X-ray scattering to study conformational changes and stabilities of IgG antibodies that are crucial to bioprocessing and biotechnology applications. We are also investigating the solution structures of complexes formed between the major complement regulator factor H and its target C3b. C3 undergo large conformational changes to form C3b, and different crystal structures reveal different domain arrangements. We wish to identify the C3b solution structure by constrained modelling in order to elucidate the molecular mechanism of how C3b is regulated by factor H.