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Complement component 3

PDB rendering based on 1c3d.
Available structures
1c3d, 1ghq, 1w2s, 2a73, 2a74, 2b39, 2gox, 2hr0, 2i07, 2ice, 2icf
Symbols C3; ASP; CPAMD1
External IDs OMIM120700 MGI88227 HomoloGene68031 GeneCards: C3 Gene
Species Human Mouse
Entrez 718 12266
Ensembl n/a ENSMUSG00000024164
UniProt n/a Q207D2
RefSeq (mRNA) NM_000064 NM_009778
RefSeq (protein) NP_000055 NP_033908
Location (UCSC) 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]



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.


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.


Complement component 3 has been shown to interact with Factor H.[10][11]


  1. ^ 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. doi:10.1073/pnas.82.3.708. PMID 2579379. PMC 397115.  
  2. ^ "Entrez Gene: C3 complement component 3".  
  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.  
  4. ^ Lachmann P (December 1975). "Genetics of the complement system". J. Med. Genet. 12 (4): 372–7. doi:10.1136/jmg.12.4.372. PMID 768477.  
  5. ^ 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" ( – Scholar search). Intern. Med. 40 (12): 1254–8. doi:10.2169/internalmedicine.40.1254. PMID 11813855.  
  6. ^ 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.  
  7. ^ 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.  
  8. ^ 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.  
  9. ^ 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.  
  10. ^ Soames, C J; Sim R B (Sep. 1997). "Interactions between human complement components factor H, factor I and C3b". Biochem. J. (ENGLAND) 326 ( Pt 2): 553–61. ISSN 0264-6021. PMID 9291131.  
  11. ^ Jokiranta, T S; Westin J, Nilsson U R, Nilsson B, Hellwage J, Löfås S, Gordon D L, Ekdahl K N, Meri S (Mar. 2001). "Complement C3b interactions studied with surface plasmon resonance technique". Int. Immunopharmacol. (Netherlands) 1 (3): 495–506. ISSN 1567-5769. PMID 11367533.  

External links

This article incorporates text from the United States National Library of Medicine, which is in the public domain.



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