Complement component 2: Difference between revisions

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Revision as of 21:44, 10 August 2021

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== Function ==

In the [[classical complement pathway|classical]] and [[lectin pathway|lectin]] pathways of [[complement activation]], formation of the [[C3-convertase]] and [[C5-convertase]]s requires binding of C2 to an activated surface-bound [[C4b]] in the presence of [[magnesium|Mg²⁺]]; the resultant C4bC2 complex isbecomes thenC3 convertase. C2 complex is cleaved by [[C1s]] or [[MASP2 (protein)|MASP2]] into C2a and C2b. It is thought that cleavage of C2 by C1s, while bound to C4b, results in a conformational rotation of C2b whereas the released C2a fragment may retain most of its original structure.

C2b is the smallest , enzymatically active fragment which is incorporated into the C3 convertase in this pathway, C4b2b (NB: [[Complement system#Complement protein fragment nomenclature|some sources now refer]] to the larger fragment of C2 as C2b, making the C3 convertase C4b2b, whereas older sources refer to the larger fragment of C2 as C2a, making the C3 convertase C4b2a). The smaller fragment, C2a (or C2b, depending on the source) is released into the fluid phase.<ref name="c2 fragment structure">{{cite journal | vauthors = Krishnan V, Xu Y, Macon K, Volanakis JE, Narayana SV | title = The structure of C2b, a fragment of complement component C2 produced during C3 convertase formation | journal = Acta Crystallographica D | volume = 65 | issue = Pt 3 | pages = 266–274 | year = 2009 | pmid = 19237749 | pmc = 2651757 | doi = 10.1107/S0907444909000389 }}</ref>