MULCh: modules for the analysis of small-angle neutron contrast variation data from biomolecular assemblies

Small-angle neutron scattering with contrast variation can fill important gaps in our understanding of biomolecular assemblies, providing constraints that can aid in the construction of molecular models and in subsequent model refinements. This paper describes the implementation of simple tools for analysing neutron contrast variation data, accessible via a user-friendly web-based interface (http://www.mmb.usyd.edu.au/NCVWeb/ ). There are three modules accessible from the website to analyse neutron contrast variation data from bimolecular complexes. The first module, Contrast, computes neutron contrasts of each component of the complex required by the other two modules; the second module, R_g, analyses the contrast dependence of the radii of gyration to yield information relating to the size and disposition of each component in the complex; and the third, Compost, decomposes the contrast variation series into composite scattering functions, which contain information regarding the shape of each component of the complex, and their orientation with respect to each other.