Cleavage of C3 by C3 convertases

Stable Identifier
R-HSA-166817
Type
Reaction [transition]
Species
Homo sapiens
Compartment
Locations in the PathwayBrowser
General
SVG |   | PPTX  | SBGN
Click the image above or here to open this reaction in the Pathway Browser
The layout of this reaction may differ from that in the pathway view due to the constraints in pathway layout

C4b and C2a bind to form the classical pathway C3-convertase (C4bC2a), C3b and the Bb fragment of Factor B form the alternative pathway C3 convertase (C3bBb). The C3(H2O):Bb C3 convertase is sometimes called the initiating convertase, and the C5 convertases also have C3 convertase activity (Rawal & Pangburn 2001).

All three pathways merge at the proteolytic cleavage of component C3 by C3 convertases to form two fragments C3b and C3a. The cleavage of component C3 exposes a reactive thioester bond on C3b, leading to the covalent attachment of C3b to glycoproteins on the target cell surface (Law SK et al. 1979; Tack BF et al. 1980). The opsonization with C3b enables the recruitment of phagocytes (Newman SL et al. 1985; Gadjeva M et al. 1998). In addition, C3b anchors the assembly of C3/C5 convertases leading to an amplification of C3 cleavage and effecting C5 activation (Fearon DT 1979; Takata Y et al 1987; Kinoshita T et al. 1988). Moreover, the activation of C3b exposes binding sites for factors B, H and I, properdin, decay accelerating factor (DAF), membrane cofactor protein (MCP), complement receptor 1 (CR1) and microbial molecules such as vaccinia virus complement-control protein and staphylococcal complement inhibitor (SCIN) from Staphylococcus aureus (Forneris F et al. 2010; Morgan HP et al. 2011; Nilsson SC et al. 2010; Lambris JD et al. 1984; Medof ME et al.1984; Barilla-LaBarca ML et al. 2002; Smith BO et al. 2002; Bernet J et al. 2004; Garcia Bl et al. 2010) . C3b associates with these molecules to mediate the activation, amplification and regulation of the complement response.

Literature References
PubMed ID Title Journal Year
15199963 The lectin-complement pathway--its role in innate immunity and evolution

Fujita, T, Matsushita, M, Endo, Y

Immunol Rev 2004
Participants
Participant Of
Catalyst Activity
Catalyst Activity
Title
serine-type endopeptidase activity of C3 convertases [plasma membrane]
Physical Entity
Activity
Orthologous Events
Authored
Reviewed
Created