C5 convertase

Definition

C5 convertase is an enzyme complex that plays a crucial role in the complement system, specifically in the activation of the complement component C5. It is responsible for cleaving C5 into C5a and C5b, which are important for promoting inflammation and forming the membrane attack complex, respectively. This process is a key step in enhancing the immune response against pathogens and contributes to the overall function of the complement activation pathways.

5 Must Know Facts For Your Next Test

1. C5 convertase can be formed through two main pathways: the classical pathway and the alternative pathway, with distinct enzyme complexes for each pathway.
2. The cleavage of C5 by C5 convertase leads to the release of C5a, a potent anaphylatoxin that promotes inflammation and recruits immune cells to sites of infection.
3. C5b generated by C5 convertase interacts with other complement proteins to initiate the formation of the Membrane Attack Complex (MAC), which directly damages pathogen membranes.
4. C5 convertase is essential for the effective opsonization of pathogens, enhancing their recognition and phagocytosis by immune cells.
5. Defects or dysregulation in C5 convertase activity can lead to increased susceptibility to infections and autoimmune conditions due to impaired immune responses.

Review Questions

• How does C5 convertase contribute to both inflammation and the formation of the Membrane Attack Complex?
  • C5 convertase plays a dual role in the immune response by cleaving complement component C5 into C5a and C5b. The release of C5a acts as an anaphylatoxin, attracting immune cells to sites of infection and promoting inflammation. Meanwhile, C5b initiates the assembly of the Membrane Attack Complex (MAC), which forms pores in pathogen membranes, leading to their lysis. This coordinated action enhances both inflammatory responses and direct pathogen destruction.
• Compare and contrast the formation of C5 convertase in the classical pathway versus the alternative pathway.
  • In the classical pathway, C5 convertase is formed by the binding of C4b2a to C3b, while in the alternative pathway, it is generated from C3bBb. Both pathways lead to the cleavage of C5, but they differ in their initiation mechanisms; the classical pathway is triggered by antigen-antibody complexes, whereas the alternative pathway is activated by pathogen surfaces. Despite these differences, both pathways converge at C5 convertase's role in generating key effector molecules like C5a and C5b.
• Evaluate how defects in C5 convertase function could impact an individual's immune response and susceptibility to disease.
  • Defects in C5 convertase function can significantly impair an individual's immune response, as this enzyme is crucial for generating important components like C5a and C5b. Reduced levels of C5a can hinder inflammation and recruitment of immune cells, making it harder for the body to fight infections. Additionally, decreased production of C5b compromises Membrane Attack Complex formation, weakening direct lysis of pathogens. This dysfunction could lead to increased susceptibility to infections and contribute to autoimmune disorders where inappropriate inflammation occurs.

Related terms

Complement System: A group of proteins that work together to enhance the immune response by marking pathogens for destruction, recruiting immune cells, and directly killing pathogens.

C3 convertase: An enzyme complex that cleaves complement component C3 into C3a and C3b, serving as a precursor to C5 convertase and crucial for initiating the complement cascade.

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