Small angle X-ray and neutron scattering (SAS) experiments and molecular modelling offer powerful tools to understand protein behaviour in solution. SAS experiments have made huge strides in the last two decades due to improved instrumentation and sources. Until recently, using atomistic simulations to interpret SAS experiments has been infrequent. This requires integrating the SAS data with molecular modelling software to reveal how biological structures change in time and space under varying experimental conditions. Recent examples of this approach include new structures for human IgG4 antibody and complement C3b that clarified their function. In order to provide open-source and user-friendly tools for SAS fits based on a web interface, CCP-SAS was set up as a joint UK/USA collaboration. Our project combines existing and novel tools for atomistic modelling trials creation (such as SASSIE) and scattering curve calculation (SCT and SASCalc) with a combined workflow and transparent access to high performance computing resources via the GenApp framework. This novel CCP-SAS approach is being evaluated using complement proteins and antibodies. The combination of crystal structures and atomistic modelling of SAS data for fragments of MASP in the complement lectin pathway using SASSIE and SCT is revealing the solution structure of the intact dimer of MASP, and new insights on its function. The combinations of new glycan modelling of hinge structures in IgA1 antibodies and crystal structures for the IgA1 Fab and Fc regions is revealing its unique structure for its monomer and dimer forms. Details of how these atomistic molecular modelling approaches were applied to these problems will be critically reviewed.