C3 Convertase

Definition

C3 convertase is an enzyme complex that plays a crucial role in the complement system, specifically in the activation of the complement protein C3. This enzyme complex cleaves C3 into C3a and C3b, which are essential for opsonization, inflammation, and the formation of the membrane attack complex. Understanding C3 convertase is key to grasping how the complement system enhances the immune response against pathogens.

5 Must Know Facts For Your Next Test

1. C3 convertase can be formed through three different pathways: classical, lectin, and alternative pathways, each initiated by distinct triggers.
2. In the classical pathway, C3 convertase is formed by the binding of C4b and C2a, while in the alternative pathway, it is formed from C3b and factor Bb.
3. The activity of C3 convertase is tightly regulated by several proteins to prevent excessive inflammation and damage to host tissues.
4. C3b generated by C3 convertase plays a pivotal role not only in opsonization but also in amplifying the complement response through positive feedback.
5. Deficiencies or dysregulation of C3 convertase activity can lead to increased susceptibility to infections and autoimmune diseases due to impaired immune function.

Review Questions

• How does C3 convertase contribute to the overall function of the complement system?
  • C3 convertase is central to the complement system as it cleaves C3 into its active forms, C3a and C3b. C3a acts as a pro-inflammatory mediator, attracting immune cells to sites of infection, while C3b opsonizes pathogens, marking them for destruction by phagocytes. This enzymatic action not only enhances inflammation but also helps clear pathogens effectively from the body.
• Discuss the differences between how C3 convertase is formed in the classical pathway versus the alternative pathway.
  • In the classical pathway, C3 convertase is formed when the C4b fragment binds to C2a, while in the alternative pathway, it is generated from the binding of C3b to factor Bb. This highlights how different initiators lead to similar outcomes within the complement system, underscoring its versatility and importance in immune responses.
• Evaluate the implications of dysregulation of C3 convertase activity on immune responses and disease susceptibility.
  • Dysregulation of C3 convertase can result in either insufficient immune responses or excessive inflammation. For instance, decreased activity may leave individuals vulnerable to infections due to inadequate opsonization and clearance of pathogens. Conversely, overactivity can lead to tissue damage and autoimmune diseases as healthy cells might be attacked. Thus, maintaining proper regulation of this enzyme complex is crucial for balanced immune function.

Related terms

Complement System: A group of proteins in the blood that work together to enhance the ability of antibodies and phagocytic cells to clear pathogens.

Opsonization:

The process by which pathogens are marked for destruction by being coated with molecules like C3b, making them more recognizable to phagocytes.

Membrane Attack Complex (MAC): A structure formed by the assembly of complement proteins that creates pores in the membranes of target cells, leading to cell lysis.