Complement component C2, inhibiting a latent serine protease in the classical pathway of complement activation

Area of Science:

• Immunology
• Biochemistry
• Molecular Biology

Background:

• The classical pathway (CP) of complement activation is crucial for innate immunity but can cause inflammatory diseases if dysregulated.
• The C3 convertase (C4bC2a) is a key, short-lived enzyme in this pathway, essential for downstream complement functions.
• Complement component 2 (C2) is a zymogen requiring cofactor-induced activation to form the C3 convertase.

Purpose of the Study:

• To investigate the intrinsic catalytic activity of C2.
• To explore C2 as a potential therapeutic target for inflammatory diseases driven by complement activation.

Main Methods:

• Enzymatic assays using C3 and chromogenic peptide substrates at varying pH.
• Characterization of C2 stability under alkaline conditions.
• Screening for small molecule inhibitors of C2 activity.
• Assays measuring inhibition of classical pathway C3 convertase, Membrane Attack Complex (MAC) formation, and hemolysis.

Main Results:

• C2 demonstrates inherent protease activity above pH 7, independent of cofactors.
• This C2 activity is stable under alkaline conditions, unlike the transient C3 convertase.
• Identified potent small molecule inhibitors targeting C2 that effectively block CP activation, MAC formation, and hemolysis.

Conclusions:

• C2 possesses intrinsic catalytic activity, presenting a new target for therapeutic intervention.
• Inhibiting C2 offers a promising strategy to control classical complement pathway activation in inflammatory conditions.