Cleavage of C3 by surface-bound C3 convertases

Stable Identifier
R-GGA-2132085
Type
Reaction [transition]
Species
Gallus gallus
Compartment
extracellular region, plasma membrane
ReviewStatus
5/5
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Cleavage of C3 by surface-bound C3 convertases
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In mammals, three pathways of complement activation - alternative, classical and lectin - merge at the key event in complement activation, the cleavage of complement C3 to C3b and C3a. Proteolytic cleavage of C3 is mediated by surface-bound C3 convertase. A single molecule of C3 convertase can enzymatically cleave hundreds of molecules of C3. The smaller fragment, anaphylatoxin C3a, initiates local inflammatory responses while the larger cleavage product C3b binds covalently to the target surface for opsonization. Opsonized particles are recognized by receptors on macrophages, and upon attachment are cleared by phagocytosis. In addition, C3b can bind C3 convertases to produce C5 convertases, C4b:C2a:C3b or C3b:C3b:Bb, which cleave C5 into C5a and C5b. C5b is an active fragment which initiates membrane attack complex (MAC) formation (Janeway CA et al. 2001).

Chicken complement factor C3 has been isolated, mapped and characterized (Laursen I & Koch C 1989; Mavrodis M et al. 1995). Chicken C3 consists of 1652 amino acids and has 54% identity with its human and mouse counterparts. Like its mammalian orthologs, chicken C3 has a two-chain structure with an alpha chain (11kDa) and a beta-chain (70kDa). Upon complement activation chicken C3 is cleaved into fragments that resemble mammalian C3a and C3b (Laursen I & Koch C 1989).

Literature References
PubMed ID Title Journal Year
  Immunobiology

Walport, MJ, Travers, P, Shlomchik, J, Janeway C, Jr

  2001
2587932 Purification of chicken C3 and a structural and functional characterization

Laursen, I, Koch, C

Scand J Immunol 1989
7532662 Isolation, primary structure, and evolution of the third component of chicken complement and evidence for a new member of the alpha 2-macroglobulin family

Mavroidis, M, Lambris, JD, Sunyer, JO

J Immunol 1995
Participants
Input
Output
Participates
as an event of
Catalyst Activity

serine-type endopeptidase activity of C3 convertases [plasma membrane]

Physical Entity
C3 convertases [plasma membrane] (Gallus gallus)
Activity
serine-type endopeptidase activity (GO:0004252)
This event is regulated
Negatively by
Regulator
CREM:C3b/C4b [plasma membrane] (Gallus gallus)
Regulator
CREG:C3 convertases [plasma membrane] (Gallus gallus)
Authored
Shamovsky, V  (2012-12-20)
Reviewed
D'Eustachio, P  (2012-11-07)
Jupe, S  (2013-01-31)
Created
Shamovsky, V  (2012-02-21)
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