Complement component 3

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PDB rendering based on 1c3d.

Available structures: 1c3d, 1ghq, 1w2s, 2a73, 2a74, 2b39, 2gox, 2hr0, 2i07, 2ice, 2icf

Identifiers

Symbols

C3; ASP; CPAMD1

External IDs

OMIM: 120700 MGI: 88227 HomoloGene: 68031

Gene ontology
Molecular function:	• endopeptidase inhibitor activity • receptor binding
Cellular component:	• extracellular region
Biological process:	• inflammatory response • complement activation, alternative pathway • complement activation, classical pathway • signal transduction • G-protein coupled receptor protein signaling pathway

Orthologs

Human

Mouse

n/a

n/a

Refseq

NM_000064 (mRNA)
NP_000055 (protein)

NM_009778 (mRNA)
NP_033908 (protein)

Location

n/a

Chr 17: 56.89 - 56.91 Mb

Pubmed search

[1]

[2]

Complement component 3, often simply called C3, is a protein of the immune system. It plays a central role in the complement system and contributes to innate immunity. In humans it is encoded on chromosome 19 by a gene called C3.^[1]^[2]

1 Function
2 Structure
3 Clinical use
4 References
5 External links

Function

C3 plays a central role in the activation of complement system.^[3] Its activation is required for both classical and alternative complement activation pathways. People with C3 deficiency are susceptible to bacteria infection.^[4]^[5]

Soluble C3-convertase, also known as C4b2a, catalyzes the proteolytic cleavage of C3 into C3a and C3b as part of the classical complement system as well as the mannan-binding lectin pathway. C3a is an anaphylotoxin, and C3b serves as an opsonizing agent. Factor I can cleave C3b into C3c and C3d, the latter of which plays a role in enhancing B cell responses. In the alternative complement pathway, C3 is cleaved by iC3Bb, another form of C3-convertase.

Structure

Several crystallographic structures of C3 have been determined and reveal that this protein contains 13 domains.^[6]^[7]^[8]^[9]

Clinical use

Levels of C3 in the blood may be measured to support or refute a particular medical diagnosis. For example, low C3 levels are associated with some types of kidney disease such as post-infectious glomerulonephritis and shunt nephritis.

References

^ de Bruijn MH, Fey GH (February 1985). "Human complement component C3: cDNA coding sequence and derived primary structure". Proc. Natl. Acad. Sci. U.S.A. 82 (3): 708–12. PMID 2579379. PMC: 397115, http://www.pnas.org/content/82/3/708.abstract.
^ "Entrez Gene: C3 complement component 3".
^ Sahu A, Lambris JD (April 2001). "Structure and biology of complement protein C3, a connecting link between innate and acquired immunity". Immunol. Rev. 180: 35–48. doi:10.1034/j.1600-065X.2001.1800103.x. PMID 11414361.
^ Lachmann P (December 1975). "Genetics of the complement system". J. Med. Genet. 12 (4): 372–7. PMID 768477.
^ Matsuyama W, Nakagawa M, Takashima H, Muranaga F, Sano Y, Osame M (December 2001). "Molecular analysis of hereditary deficiency of the third component of complement (C3) in two sisters". Intern. Med. 40 (12): 1254–8. PMID 11813855, http://joi.jlc.jst.go.jp/JST.Journalarchive/internalmedicine1992/40.1254?from=PubMed.
^ Janssen BJ, Huizinga EG, Raaijmakers HC, Roos A, Daha MR, Nilsson-Ekdahl K, Nilsson B, Gros P (September 2005). "Structures of complement component C3 provide insights into the function and evolution of immunity". Nature 437 (7058): 505–11. doi:10.1038/nature04005. PMID 16177781.
^ Janssen BJ, Christodoulidou A, McCarthy A, Lambris JD, Gros P (November 2006). "Structure of C3b reveals conformational changes that underlie complement activity". Nature 444 (7116): 213–6. doi:10.1038/nature05172. PMID 17051160.
^ Wiesmann C, Katschke KJ, Yin J, Helmy KY, Steffek M, Fairbrother WJ, McCallum SA, Embuscado L, DeForge L, Hass PE, van Lookeren Campagne M (November 2006). "Structure of C3b in complex with CRIg gives insights into regulation of complement activation". Nature 444 (7116): 217–20. doi:10.1038/nature05263. PMID 17051150.
^ Fredslund F, Jenner L, Husted LB, Nyborg J, Andersen GR, Sottrup-Jensen L (August 2006). "The structure of bovine complement component 3 reveals the basis for thioester function". J. Mol. Biol. 361 (1): 115–27. doi:10.1016/j.jmb.2006.06.009. PMID 16831446.

External links

MeSH Complement+C3

v • d • e

Proteins: complement system (C, L, A)

Activators/enzymes

Early	C: C1Q/C1R/C1S - C4 (C4a) - C2 L: MASP1/MASP2 - MBL

Middle	CLA: C3 (C3a, C3b/iC3b) - C5 (C5a) A: Factor B - Factor D - Factor P/Properdin CLA: C3-convertase - C5-convertase

Late	CLA: MAC (C6, C7, C8, C9)

Inhibitors

CLA: C1-inhibitor - Decay accelerating factor - Factor I

CL: C4BP

A: Factor H

Complement receptors

CR1 - CR2 - CR3 - CR4 - CD11b/CD11c/CD18 - Anaphylatoxin (C3a, C5a)

v • d • e Acute phase proteins

Amyloid	SAP - SAA

Other positive	Alpha 1-antichymotrypsin - Alpha 1-antitrypsin - Alpha 2-macroglobulin - C-reactive protein - Ceruloplasmin - C3 - Fibrin - Haptoglobin - Haemopexin - Orosomucoid - Transferrin

Negative	Serum albumin