Complement C3

Function

Complement C3 (CC3) activates the complement system which is part of the immune response. CC3 is proteolytically cleaved by C3 convertase to C3a (residues 672-748) and C3b (residues 23-667, 749-1663). C3a is a mediator of local inflammatory processes. C3b binds covalently to cell surface carbohydrates or immune aggregates. Breakdown of C3b generates the fragment C3d (residues 996-1287) which binds to antigens enhancing their uptake by B cells. C3c is another C3b cleavage product residues: 23-664, 749-954, 1321-1663.

Disease

Relevance

Structural highlights

3D structures of complement C3

Updated on 14-July-2014

CC3

2a73 – hCC3 – human
2b39 – bCC3 – bovine

CC3a (anaphylatoxin)

4hw5, 4hwj, 4i6o – hCC3

CC3b

2hr0, 2i07 – hCC3 β+α’ chains
2icf – hCC3 α+β chains + protein CRIG
3g6j – hCC3 α+β chains + antibody
2xwb – hCC3 α+β chains + complement factor B + complement factor D
2xwj – hCC3 α+β chains (mutant) + complement factor B
2wii – hCC3 α+β chains + complement factor H 1-4 sushi domains
3l5n, 3ohx – hCC3 α+β chains + staphylococcal complement inhibitor
2win – hCC3 α+β chains + complement factor B BB fragment + staphylococcal complement inhibitor

CC3c

2a74 – hCC3
2qki – hCC3 + compstatin
3l3o, 3nms – hCC3 + staphylococcal complement inhibitor
2ice – hCC3 α+β chains + protein CRIG
3t4a – hCC3 α+β chains + fibrinogen-binding protein

CC3d

1c3d – hCC3 (mutant)
1w2s, 3oed – hCC3 1-2 sushi domains + complement receptor type 2 precursor
2gox, 3d5r, 3d5s – hCC3 α chain fragment + fibrinogen-binding protein
2noj – hCC3 α chain fragment (mutant) + EFB homologous protein
2wy7, 2wy8 – hCC3 α chain fragment (mutant) + IGG-binding protein
3oxu – hCC3 α chain fragment (mutant) + HF protein
4m76 – hCC3 α chain fragment (mutant) + integrin α-M
2xqw – hCC3 + complement factor H 19-20 sushi domains
3rj3 – hCC3 α chain fragment + complement factor H-related protein
1qqf – rCC3 G fragment - rat
1qsj – rCC3 G fragment (mutant)

References