Complement component 1q: Difference between revisions

Revision as of 18:43, 21 February 2021

Revision as of 20:36, 9 March 2021

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== Domain ==

The C1q ___domain is a conserved [[protein ___domain]]. [[C1Q complex|C1q]] is a subunit of the C1 [[enzyme]] [[Protein complex|complex]] that activates the [[blood serum|serum]] [[complement system]]. C1q comprises 6 A, 6 B and 6 C [[polymer|chain]]s. These share the same topology, each possessing a small, globular [[N-terminal]] ___domain, a collagen-like Gly/Pro-rich central region, and a [[conserved sequence|conserved]] C-terminal region, the C1q ___domain.<ref name="pmid1706597">{{cite journal |vauthors=Sellar GC, Blake DJ, Reid KB | title = Characterization and organization of the genes encoding the A-, B- and C-chains of human complement subcomponent C1q. The complete derived amino acid sequence of human C1q | journal = Biochem. J. | volume = 274 | issue = 2| pages = 481–90 |date=March 1991 | pmid = 1706597 | pmc = 1150164 | doi = 10.1042/bj2740481}}</ref> The C1q protein is produced in collagen-producing [[cell (biology)|cell]]s and shows [[sequence (biology)|sequence]] and structural similarity to [[collagen]]s VIII and X.<ref name="pmid2591537">{{cite journal |vauthors=Petry F, Reid KB, Loos M | title = Molecular cloning and characterization of the complementary DNA coding for the B-chain of murine Clq | journal = FEBS Lett. | volume = 258 | issue = 1 | pages = 89–93 |date=November 1989 | pmid = 2591537 | doi = 10.1016/0014-5793(89)81622-9| doi-access = free }}</ref><ref name="pmid2019595">{{cite journal |vauthors=Muragaki Y, Jacenko O, Apte S, Mattei MG, Ninomiya Y, Olsen BR | title = The alpha 2(VIII) collagen gene. A novel member of the short chain collagen family located on the human chromosome 1 | journal = J. Biol. Chem. | volume = 266 | issue = 12 | pages = 7721–7 |date=April 1991 | doi = 10.1016/S0021-9258(20)89508-8 | pmid = 2019595 }}</ref>

==Function==

[[File:Complement pathway.svg|thumb|270px|left|The classical and alternative complement pathways. C1q is the orange part of the [[C1 complex]] at the top of the image.]]

It is assumed that the globular ends are the sites for multivalent attachment to the complement fixing sites in immune complexed immunoglobulin. Patients suffering from Lupus erythematosus often have deficient expression of C1q. Genetic deficiency of C1q is extremely rare (approximately 75 known cases) although the majority (>90%) of those suffer from [[Systemic lupus erythematosus|SLE]]. C1q may also play a central role in the aging of cells.<ref name="Secret of ageing found: Japanese scientists pave way to everlasting life">{{cite web|title=Secret of ageing found: Japanese scientists pave way to everlasting life|url=http://www.rt.com/news/japan-scientists-stop-ageing-461/|work=Russia Today|publisher=Russia Today|accessdateaccess-date=10 June 2012}}</ref>

C1q associates with C1r and C1s in order to yield the [[C1 complex]] (''C1qr²s²''), the first component of the serum [[complement system]]. Deficiency of C1q has been associated with [[lupus erythematosus]] and [[glomerulonephritis]].<ref name="entrez ciqa"/>