Reactome | C4b-binding protein binds C4b

C4b-binding protein binds C4b

Stable Identifier

R-HSA-977626

Type

Reaction [binding]

Species

Homo sapiens

Compartment

plasma membrane, extracellular region

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The most abundant form of C4b-binding protein (C4BP) consists of seven alpha-chains (70kDa) and one beta-chain (45kDa) all linked by disulphide bonds to form a native protein with a molecular weight of 570kDa (Hilarp et al. 1989). Each alpha chain can bind C4b; it is not known whether full occupancy is necessary for subsequent events. The beta chain binds and inactivates Protein S, a component of the coagulation system. C4BP down-regulates complement activity in several ways: It binds to C4b thus inhibiting the formation of the classical pathway C3 convertase C4bC2a; it acts as a decay accelerating factor for existing convertases, probably by promoting dissociation of C2a; it is a cofactor in Factor I mediated C4b proteolysis.

Literature References

PubMed ID	Title	Journal	Year
670886	Human C4-binding protein. I. Isolation and characterization Scharfstein, J, Ferreira, A, Gigli, I, Nussenzweig, V	J Exp Med	1978
6222381	Visualization of human C4b-binding protein and its complexes with vitamin K-dependent protein S and complement protein C4b Dahlback, B, Smith, CA, Muller-Eberhard, HJ	Proc Natl Acad Sci U S A	1983
6334079	Characterization of the interaction of human C4b-binding protein with physiological ligands Ziccardi, RJ, Dahlback, B, Muller-Eberhard, HJ	J Biol Chem	1984