C3a (complement)

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The classical and alternative complement pathways.

C3a is one of the proteins formed by the cleavage of complement component 3; the other is C3b. C3a is a 77 residue peptide that binds to the C3a receptor (C3aR) a class A G protein-coupled receptor. It stimulates mast cell degranulation, thus triggering an immune response.

C3a plays an important role in chemotaxis, though not as important a role as C5a.[1]

It is also an anaphylatoxin and the precursor of the important cytokine (adipokine) ASP through its interaction with carboxypeptidase B.[2] Because C3a is rapidly degraded in serum, stable small molecule agonists and antagonists may be used as tools to probe the physiological effects of C3a in vivo.[3][4][5]


  1. ^ Andreas Klos, Elisabeth Wende, Kathryn J. Wareham, and Peter N. Monk (2013). "International Union of Pharmacology. LXXXVII. Complement Peptide C5a, C4a, and C3a Receptors". Pharmacological Reviews 65 (1): 500–543. doi:10.1124/pr.111.005223. PMID 23383423. 
  2. ^ Onat A, Can G, Rezvani R, Cianflone K (June 2011). "Complement C3 and cleavage products in cardiometabolic risk". Clinica Chimica Acta (Amsterdam: Elsevier) 412 (13-14): 1171–9. doi:10.1016/j.cca.2011.03.005. PMID 21419112. 
  3. ^ Reid, RC; Yau, MK; Singh, R; Hamidon, JK; Reed, AN; Chu, P; Suen, JY; Stoermer, MJ; Blakeney, JS; Lim, J; Faber, JM; Fairlie, DP (2013). "Downsizing a human inflammatory protein to a small molecule with equal potency and functionality.". Nature communications 4: 2802. doi:10.1038/ncomms3802. PMID 24257095. 
  4. ^ Reid, Robert C.; Yau, Mei-Kwan; Singh, Ranee; Hamidon, Johan K.; Lim, Junxian; Stoermer, Martin J.; Fairlie, David P. (23 October 2014). "Potent Heterocyclic Ligands for Human Complement C3a Receptor". Journal of Medicinal Chemistry 57 (20): 8459–8470. doi:10.1021/jm500956p. PMID 25259874. 
  5. ^ Reid, Robert C.; Yau, Mei-Kwan; Singh, Ranee; Lim, Junxian; Fairlie, David P. (27 August 2014). "Stereoelectronic Effects Dictate Molecular Conformation and Biological Function of Heterocyclic Amides". Journal of the American Chemical Society 136 (34): 11914–11917. doi:10.1021/ja506518t. PMID 25102224. 
  • Dinasarapu, A R; Chandrasekhar, A; Sahu, A; Subramaniam, S (2012). "Complement C3 (Human)". UCSD Molecule Pages. doi:10.6072/H0.MP.A004235.01. 

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