Bert J. C. Janssen

Bert J. C. Janssen is the first author of a 2005 structural study of Complement C3 and its processed fragment C3c. The team determined crystal structures that connected the arrangement of protein domains to activation and regulation in the complement system.^[ref]

The structures helped explain how a reactive thioester, needed for later covalent attachment, can remain protected against premature hydrolysis. Comparing the native and processed forms also revealed substantial changes in domain arrangement.^[ref]

The comparison is specifically Complement C3 versus C3c. It is not a direct pair of structures showing native Complement C3 and active C3b. Keeping the fragments distinct matters because different stages of processing have different biological roles: an informative structural difference is not automatically the exact movement that creates an active intermediate.