The molecular switches controlling the interaction between complement proteases of the classical and lectin pathways and their substrates.

Complement represents a major bridge between the innate and adaptive immune systems of the body. It plays a vital role in host defences against pathogens, but has also been implicated in numerous inflammatory diseases. The system has been the subject of intensive research in recent times with a number of key structural insights into the functioning of the system. Here, we will give an overview of the activation of each pathway, following which recent developments in our understanding of the mechanisms governing the interaction between enzymes and substrates in the classical and lectin pathways in particular will be discussed.