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.
C3c is another C3b cleavage product residues: 23-664, 749-954, 1321-1663.^[1]
C3d is a fragment generated by C3b(residues 996-1287) which binds to antigens enhancing their uptake by B cells^[2].

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(PDB code 2icf).^[3]

Disease

A mutation in CC3 cause the progressive kidney disease: dense deposit disease. Other mutations are associated with recurrent bacterial infections.

Relevance

Low levels of CC3 in the blood are associated with some kidney diseases.

3D structures of complement C3

Complement C3 3D structures

Structure of human glycosylated complement C3b α (magenta) and β (salmon) chains complex with protein CRIG (cyan) and Ca+2 ion (green) (PDB code 2icf).

Drag the structure with the mouse to rotate

ReferencesReferences

↑ Sahu A, Lambris JD. Structure and biology of complement protein C3, a connecting link between innate and acquired immunity. Immunol Rev. 2001 Apr;180:35-48. PMID:11414361
↑ Toapanta FR, Ross TM. Complement-mediated activation of the adaptive immune responses: role of C3d in linking the innate and adaptive immunity. Immunol Res. 2006;36(1-3):197-210. PMID:17337780 doi:10.1385/IR:36:1:197
↑ Wiesmann C, Katschke KJ, Yin J, Helmy KY, Steffek M, Fairbrother WJ, McCallum SA, Embuscado L, DeForge L, Hass PE, van Lookeren Campagne M. Structure of C3b in complex with CRIg gives insights into regulation of complement activation. Nature. 2006 Nov 9;444(7116):217-20. Epub 2006 Oct 15. PMID:17051150 doi:10.1038/nature05263

Proteopedia Page Contributors and Editors (what is this?)Proteopedia Page Contributors and Editors (what is this?)

Michal Harel, Alexander Berchansky

[1] Sahu A, Lambris JD. Structure and biology of complement protein C3, a connecting link between innate and acquired immunity. Immunol Rev. 2001 Apr;180:35-48. PMID:11414361

[2] Toapanta FR, Ross TM. Complement-mediated activation of the adaptive immune responses: role of C3d in linking the innate and adaptive immunity. Immunol Res. 2006;36(1-3):197-210. PMID:17337780 doi:10.1385/IR:36:1:197

[3] Wiesmann C, Katschke KJ, Yin J, Helmy KY, Steffek M, Fairbrother WJ, McCallum SA, Embuscado L, DeForge L, Hass PE, van Lookeren Campagne M. Structure of C3b in complex with CRIg gives insights into regulation of complement activation. Nature. 2006 Nov 9;444(7116):217-20. Epub 2006 Oct 15. PMID:17051150 doi:10.1038/nature05263

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