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Added bibcode. | Use this bot. Report bugs. | Suggested by Abductive | Category:Complement system | #UCB_Category 2/48

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{{short description|Protein fragment}}
{{cs1 config|name-list-style=vanc}}
{{infobox protein
| Name = complement component 5
| caption = Schematic representation of three-dimensional structure of complement 5a
| image = C5a-3D.png
| width =
| HGNCid = 1331
| Symbol = C5
| AltSymbols =
| EntrezGene = 727
| OMIM = 120900
| RefSeq = NM_001735
| UniProt = P01031
| PDB =
| ECnumber =
| Chromosome = 9
| Arm = q
| Band = 34.1
| LocusSupplementaryData =
}}
'''C5a''' is a protein fragment released from cleavage of [[Complement component 5|complement component C5]] by protease [[C5-convertase]] into C5a and C5b fragments. C5b is important in late events of the complement cascade, an orderly series of reactions which coordinates several basic defense mechanisms, including formation of the [[membrane attack complex]] (MAC), one of the most basic weapons of the innate immune system, formed as an automatic response to intrusions from foreign particles and microbial invaders. It essentially pokes microscopic pinholes in these foreign objects, causing loss of water and sometimes death. C5a, the other cleavage product of C5, acts as a highly inflammatory peptide, encouraging complement activation, formation of the MAC, attraction of innate immune cells, and histamine release involved in allergic responses. The origin of C5 is in the [[hepatocyte]], but its synthesis can also be found in [[macrophage]]s, where it may cause local increase of C5a. C5a is a chemotactic agent and an anaphylatoxin; it is essential in the innate immunity but it is also linked with the adaptive immunity. The increased production of C5a is connected with a number of inflammatory diseases.<ref name="pmid19464229">{{cite journal | vauthors = Manthey HD, Woodruff TM, Taylor SM, Monk PN | title = Complement component 5a (C5a) | journal = The International Journal of Biochemistry & Cell Biology | volume = 41 | issue = 11 | pages = 2114–2117 | date = November 2009 | pmid = 19464229 | doi = 10.1016/j.biocel.2009.04.005 }}</ref>

== Structure ==
Human polypeptide C5a contains 74 amino acids and has 11kDa. NMR spectroscopy proved that the molecule is composed of four helices and connected by peptide loops with three disulphide bonds between helix IV and II, III. There is a short 1.5 turn helix on [[N-terminus]] but all agonist activity take place in the [[C-terminus]]. C5a is rapidly metabolised by a serum enzyme [[carboxypeptidase B]] to a 72 amino acid form C5a des-Arg without C terminal arginine.<ref>{{cite journal | vauthors = Klos A, Wende E, Wareham KJ, Monk PN | title = International Union of Basic and Clinical Pharmacology. [corrected]. LXXXVII. Complement peptide C5a, C4a, and C3a receptors | journal = Pharmacological Reviews | volume = 65 | issue = 1 | pages = 500–543 | date = January 2013 | pmid = 23383423 | doi = 10.1124/pr.111.005223 | doi-access = free }}</ref><ref name="pmid15040586">{{cite journal | vauthors = Ward PA | title = The dark side of C5a in sepsis | journal = Nature Reviews. Immunology | volume = 4 | issue = 2 | pages = 133–142 | date = February 2004 | pmid = 15040586 | doi = 10.1038/nri1269 | s2cid = 22630287 }}</ref>

==Functions==
C5a is an [[anaphylatoxin]], causing increased expression of adhesion molecules on endothelium, contraction of smooth muscle, and increased vascular permeability. C5a des-Arg is a much less potent anaphylatoxin. Both C5a and C5a des-Arg can trigger [[mast cell]] degranulation, releasing proinflammatory molecules [[histamine]] and [[TNF-α]]. C5a is also an effective [[Chemotaxis#Chemotactic ligands|chemoattractant]],<ref>{{cite journal | vauthors = Seow V, Lim J, Cotterell AJ, Yau MK, Xu W, Lohman RJ, Kok WM, Stoermer MJ, Sweet MJ, Reid RC, Suen JY, Fairlie DP | display-authors = 6 | title = Receptor residence time trumps drug-likeness and oral bioavailability in determining efficacy of complement C5a antagonists | journal = Scientific Reports | volume = 6 | issue = 1 | pages = 24575 | date = April 2016 | pmid = 27094554 | doi = 10.1038/srep24575 | pmc = 4837355 | bibcode = 2016NatSR...624575S }}</ref> initiating accumulation of complement and phagocytic cells at sites of infection or recruitment of antigen-presenting cells to lymph nodes.<ref>{{cite journal | vauthors = Gerard NP, Gerard C | title = The chemotactic receptor for human C5a anaphylatoxin | journal = Nature | volume = 349 | issue = 6310 | pages = 614–617 | date = February 1991 | pmid = 1847994 | doi = 10.1038/349614a0 | bibcode = 1991Natur.349..614G | s2cid = 4338594 }}</ref>
C5a plays a key role in increasing migration and adherence of neutrophils and monocytes to vessel walls. White blood cells are activated by upregulation of [[integrin]] [[avidity]], the [[Prostaglandin#Biosynthesis|lipoxygenase pathway]] and [[arachidonic acid]] metabolism.
C5a also modulates the balance between activating versus inhibitory [[Immunoglobulin G|IgG]] [[Fc receptor]]s on leukocytes, thereby enhancing the [[Autoimmunity|autoimmune]] response.<ref name="pmid19464229"/>

==Binding process==
C5a interact with [[Receptor (biochemistry)|receptor]] protein C5a Receptor 1 ([[C5a receptor|C5aR1]]) on the surface of target cells such as macrophages, neutrophils and endothelial cells. C5aR1 is a member of the [[G-protein-coupled receptor]] superfamily of proteins, predicted to have seven transmembrane helical domains of largely hydrophobic [[amino acid]] residues, forming three intra- and three extra-cellular loops, with an extracellular N-terminus and an intracellular C-terminus.

C5a binding to the receptor is a two-stage process: an interaction between basic residues in the helical core of C5a and acidic residues in the extracellular N-terminal domain allows the C-terminus of C5a to bind to residues in the receptor transmembrane domains. The latter interaction leads to receptor activation, and the transduction of the ligand binding signal across the cell [[plasma membrane]] to the cytoplasmic G protein [[Gi alpha subunit|G<sub>i</sub>]] type [[GNAI2]].<ref>{{cite web | vauthors = Fujita T | date = 14 October 1999 | veditors = Boulay F | url = http://mpr.nci.nih.gov/prow/guide/666919736_g.htm | work = Protein Reviews on the Web | title = PROW and IWHLDA present the GUIDE on: CD88 | archive-url = https://web.archive.org/web/20080724181852/http://mpr.nci.nih.gov/prow/guide/666919736_g.htm | archive-date=2008-07-24 }}</ref>

Sensitivity of C5aR1 to C5a stimulation is enhanced by lipopolysaccharides exposure. C5a, acting via C5aR1, is shown to differentially modulate lipopolysaccharides-induced inflammatory responses in primary human monocytes versus macrophages,<ref>{{cite journal | vauthors = Seow V, Lim J, Iyer A, Suen JY, Ariffin JK, Hohenhaus DM, Sweet MJ, Fairlie DP | display-authors = 6 | title = Inflammatory responses induced by lipopolysaccharide are amplified in primary human monocytes but suppressed in macrophages by complement protein C5a | journal = Journal of Immunology | volume = 191 | issue = 8 | pages = 4308–4316 | date = October 2013 | pmid = 24043889 | doi = 10.4049/jimmunol.1301355 | s2cid = 207429042 | doi-access = free }}</ref> yet this is not due to C5aR1 upregulation.<ref>{{cite journal | vauthors = Raby AC, Holst B, Davies J, Colmont C, Laumonnier Y, Coles B, Shah S, Hall J, Topley N, Köhl J, Morgan BP, Labéta MO | display-authors = 6 | title = TLR activation enhances C5a-induced pro-inflammatory responses by negatively modulating the second C5a receptor, C5L2 | journal = European Journal of Immunology | volume = 41 | issue = 9 | pages = 2741–2752 | date = September 2011 | pmid = 21630250 | pmc = 3638321 | doi = 10.1002/eji.201041350 }}</ref> C5L2 is another C5a receptor that is thought to regulate the C5a-C5aR1 effects. There is apparently contradictory evidence showing decoy receptor activity conferring anti-inflammatory properties and also signalling activity conferring pro-inflammatory properties.<ref name="pmid= 23383423">{{cite journal | vauthors = Klos A, Wende E, Wareham KJ, Monk PN | title = International Union of Basic and Clinical Pharmacology. [corrected]. LXXXVII. Complement peptide C5a, C4a, and C3a receptors | journal = Pharmacological Reviews | volume = 65 | issue = 1 | pages = 500–543 | date = January 2013 | pmid = 23383423 | doi = 10.1124/pr.111.005223 | doi-access = free }}</ref><ref name="pmid19464229"/>

==Diseases==
C5a is a powerful inflammatory mediator, and seems to be a key factor in the development of pathology of many inflammatory diseases involving the complement system such as sepsis, rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythemotosis, psoriasis. The inhibitor of C5a that can block its effects would be helpful in medical applications.
Another candidate is PMX53 or PMX205 that is highly specific for CD88 and effectively reduces inflammatory response.<ref name="pmid16816116">{{cite journal | vauthors = Woodruff TM, Crane JW, Proctor LM, Buller KM, Shek AB, de Vos K, Pollitt S, Williams HM, Shiels IA, Monk PN, Taylor SM | display-authors = 6 | title = Therapeutic activity of C5a receptor antagonists in a rat model of neurodegeneration | journal = FASEB Journal | volume = 20 | issue = 9 | pages = 1407–1417 | date = July 2006 | pmid = 16816116 | doi = 10.1096/fj.05-5814com | doi-access = free | s2cid = 9206660 }}</ref><ref name="pmid22924972">{{cite journal | vauthors = Jain U, Woodruff TM, Stadnyk AW | title = The C5a receptor antagonist PMX205 ameliorates experimentally induced colitis associated with increased IL-4 and IL-10 | journal = British Journal of Pharmacology | volume = 168 | issue = 2 | pages = 488–501 | date = January 2013 | pmid = 22924972 | pmc = 3572573 | doi = 10.1111/j.1476-5381.2012.02183.x }}</ref> C5a has been identified as a key mediator of [[neutrophil]] dysfunction in [[sepsis]], with antibody blockade of C5a improving outcomes in experimental models.<ref>{{cite journal | vauthors = Huber-Lang MS, Younkin EM, Sarma JV, McGuire SR, Lu KT, Guo RF, Padgaonkar VA, Curnutte JT, Erickson R, Ward PA | display-authors = 6 | title = Complement-induced impairment of innate immunity during sepsis | journal = Journal of Immunology | volume = 169 | issue = 6 | pages = 3223–3231 | date = September 2002 | pmid = 12218141 | doi = 10.4049/jimmunol.169.6.3223 | doi-access = free }}</ref> This has also been shown in humans,<ref>{{cite journal | vauthors = Conway Morris A, Kefala K, Wilkinson TS, Dhaliwal K, Farrell L, Walsh T, Mackenzie SJ, Reid H, Davidson DJ, Haslett C, Rossi AG, Sallenave JM, Simpson AJ | display-authors = 6 | title = C5a mediates peripheral blood neutrophil dysfunction in critically ill patients | journal = American Journal of Respiratory and Critical Care Medicine | volume = 180 | issue = 1 | pages = 19–28 | date = July 2009 | pmid = 19324972 | pmc = 2948533 | doi = 10.1164/rccm.200812-1928OC }}</ref> with C5a-mediated neutrophil dysfunction predicting subsequent nosocomial infection<ref>{{cite journal | vauthors = Morris AC, Brittan M, Wilkinson TS, McAuley DF, Antonelli J, McCulloch C, Barr LC, McDonald NA, Dhaliwal K, Jones RO, Mackellar A, Haslett C, Hay AW, Swann DG, Anderson N, Laurenson IF, Davidson DJ, Rossi AG, Walsh TS, Simpson AJ | display-authors = 6 | title = C5a-mediated neutrophil dysfunction is RhoA-dependent and predicts infection in critically ill patients | journal = Blood | volume = 117 | issue = 19 | pages = 5178–5188 | date = May 2011 | pmid = 21292772 | doi = 10.1182/blood-2010-08-304667 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Conway Morris A, Datta D, Shankar-Hari M, Stephen J, Weir CJ, Rennie J, Antonelli J, Bateman A, Warner N, Judge K, Keenan J, Wang A, Burpee T, Brown KA, Lewis SM, Mare T, Roy AI, Hulme G, Dimmick I, Rossi AG, Simpson AJ, Walsh TS | display-authors = 6 | title = Cell-surface signatures of immune dysfunction risk-stratify critically ill patients: INFECT study | journal = Intensive Care Medicine | volume = 44 | issue = 5 | pages = 627–635 | date = May 2018 | pmid = 29915941 | pmc = 6006236 | doi = 10.1007/s00134-018-5247-0 }}</ref> and death from sepsis.<ref>{{cite journal | vauthors = Conway Morris A, Anderson N, Brittan M, Wilkinson TS, McAuley DF, Antonelli J, McCulloch C, Barr LC, Dhaliwal K, Jones RO, Haslett C, Hay AW, Swann DG, Laurenson IF, Davidson DJ, Rossi AG, Walsh TS, Simpson AJ | display-authors = 6 | title = Combined dysfunctions of immune cells predict nosocomial infection in critically ill patients | journal = British Journal of Anaesthesia | volume = 111 | issue = 5 | pages = 778–787 | date = November 2013 | pmid = 23756248 | doi = 10.1093/bja/aet205 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Unnewehr H, Rittirsch D, Sarma JV, Zetoune F, Flierl MA, Perl M, Denk S, Weiss M, Schneider ME, Monk PN, Neff T, Mihlan M, Barth H, Gebhard F, Ward PA, Huber-Lang M | display-authors = 6 | title = Changes and regulation of the C5a receptor on neutrophils during septic shock in humans | journal = Journal of Immunology | volume = 190 | issue = 8 | pages = 4215–4225 | date = April 2013 | pmid = 23479227 | doi = 10.4049/jimmunol.1200534 | doi-access = free }}</ref> Recent data demonstrates that C5a not only impairs phagocytosis by neutrophils but also impairs phagosomal maturation,<ref>{{cite journal | vauthors = Wood AJ, Vassallo AM, Ruchaud-Sparagano MH, Scott J, Zinnato C, Gonzalez-Tejedo C, Kishore K, D'Santos CS, Simpson AJ, Menon DK, Summers C, Chilvers ER, Okkenhaug K, Morris AC | display-authors = 6 | title = C5a impairs phagosomal maturation in the neutrophil through phosphoproteomic remodeling | journal = JCI Insight | volume = 5 | issue = 15 | date = August 2020 | pmid = 32634128 | pmc = 7455072 | doi = 10.1172/jci.insight.137029 | doi-access = free }}</ref> inducing a marked alteration in the neutrophil phosphoproteomic response to bacterial targets. C5a binding to [[C5a receptor|C5aR1]] and C5aR2 ([[C5L2]]) mediates the formation of neutrophil extracellular traps and release of cytotoxic histones to the extracellular space, which is believed to act as a pathogenetic process of acute respiratory distress syndrome ([[ARDS]])<ref name = "pmid23982144">{{cite journal | vauthors = Bosmann M, Grailer JJ, Ruemmler R, Russkamp NF, Zetoune FS, Sarma JV, Standiford TJ, Ward PA | display-authors = 6 | title = Extracellular histones are essential effectors of C5aR- and C5L2-mediated tissue damage and inflammation in acute lung injury | journal = FASEB Journal | volume = 27 | issue = 12 | pages = 5010–5021 | date = December 2013 | pmid = 23982144 | pmc = 3834784 | doi = 10.1096/fj.13-236380 | doi-access = free }}</ref> and promote tumor growth and metastasis.<ref name = "pmid34971753">{{cite journal | vauthors = Ortiz-Espinosa S, Morales X, Senent Y, Alignani D, Tavira B, Macaya I, Ruiz B, Moreno H, Remírez A, Sainz C, Rodriguez-Pena A, Oyarbide A, Ariz M, Andueza MP, Valencia K, Teijeira A, Hoehlig K, Vater A, Rolfe B, Woodruff TM, Lopez-Picazo JM, Vicent S, Kochan G, Escors D, Gil-Bazo I, Perez-Gracia JL, Montuenga LM, Lambris JD, Ortiz de Solorzano C, Lecanda F, Ajona D, Pio R | display-authors = 6 | title = Complement C5a induces the formation of neutrophil extracellular traps by myeloid-derived suppressor cells to promote metastasis | journal = Cancer Letters | volume = 529 | pages = 70–84 | date = March 2022 | pmid = 34971753 | doi = 10.1016/j.canlet.2021.12.027 | s2cid = 245556050 | doi-access = }}</ref>

== References ==
{{reflist}}

== External links ==
* {{MeshName|Complement+C5a}}

{{Complement system}}

[[Category:Complement system]]
[[Category:Molecular biology]]

Complement component 5a - Revision history

imported>Citation bot: Added bibcode. | Use this bot. Report bugs. | Suggested by Abductive | Category:Complement system | #UCB_Category 2/48