Alternative pathway C5 convertase (C3bBbC3b) (C3bBbC3b)

The alternative pathway C5 convertase is a critical enzymatic complex of the innate immune system, specifically the complement cascade (StatPearls: Complement System, 2023). It is composed of two molecules of C3b and one molecule of the activated serine protease Bb, forming the C3bBbC3b complex (PubMed: PMID 21115937). This complex is responsible for the proteolytic cleavage of complement component C5 into C5a, a potent anaphylatoxin, and C5b, which initiates the assembly of the membrane attack complex (MAC) (UniProt: P01024). Overactivation or lack of regulation of this convertase leads to host tissue damage in diseases such as paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS) (PubMed: PMID 28273486). Therapeutic strategies involve either inhibiting the formation of the convertase by targeting components like Factor B (e.g., iptacopan) or Factor D (e.g., danicopan), or by blocking the substrate C5 itself (e.g., eculizumab) to prevent downstream inflammation and cell lysis (FDA: Fabhalta Prescribing Information, 2023). By modulating this activity, clinicians can manage complement-mediated hemolysis and organ damage.

Other names

C3b2BbC3bBb3bAlternative C5 convertaseC5 convertase (Alternative Pathway)

Inhibition of the proteolytic cleavage of complement component C5 into C5a and C5b, preventing terminal complement cascade activation.