Small-angle X-ray scattering and crystallography: a winning combination for exploring the multimodular organization of cellulolytic macromolecular complexes.

Small-angle X-ray scattering (SAXS) is an increasingly popular method to obtain low-resolution structures of complex macromolecules and their complexes in solution, in part due to recent technical and computational advances that make this method more and more accessible. However, to obtain unambiguous molecular interpretation from SAXS envelopes, the efficient use of and combination with additional structural methods are crucial. The multimodular character of cellulases and their assemblage in the cellulosome are ideally analyzed by such a combination of structural methods. Here, we describe how information from different sources can be combined with SAXS to determine the molecular organization and we depict the recent advancements and trends that are leading to a more comprehensive picture of the molecular architecture of these multimodular enzymes and their organization in macro-assemblages such as cellulosomes.