Putting the structure into complement.

In a field where structure has finally begun to have a real impact, a series of new structures over the last two years have further extended our understanding of some of the critical regulatory events of the complement system. Notably, information has begun to flow from larger assemblies of components which allow insight into the often transient assemblies critical to complement regulation at the cell surface. This review will summarise the key structures determined since the last International Complement Workshop and the insights these have given us, before highlighting some questions that still require molecular frameworks to drive understanding.