C3 Convertase

Definition

C3 convertase is a key enzyme complex in the complement system, a critical part of the innate immune response. It is responsible for activating the central component of the complement cascade, the C3 protein, leading to the generation of various effector molecules that help eliminate pathogens and damaged cells.

5 Must Know Facts For Your Next Test

1. C3 convertase is an enzyme complex that consists of C4b and C2a in the classical and lectin pathways, or Bb and C3b in the alternative pathway.
2. The formation of C3 convertase is a critical step in the activation of the complement system, as it leads to the cleavage of C3 into C3a and C3b.
3. C3b, a product of C3 cleavage, can then go on to form additional C3 convertase, amplifying the complement response.
4. C3 convertase is tightly regulated by complement regulatory proteins to prevent excessive or uncontrolled activation of the complement system.
5. Dysregulation of C3 convertase has been implicated in the pathogenesis of various inflammatory and autoimmune diseases.

Review Questions

• Explain the role of C3 convertase in the activation of the complement system.
  • C3 convertase is a crucial enzyme complex that initiates the central step in the complement cascade. By cleaving the C3 protein into C3a and C3b, C3 convertase sets off a series of events that lead to the generation of various effector molecules. These effector molecules help mark pathogens for elimination, recruit inflammatory cells, and directly lyse target cells. The formation of C3 convertase is therefore a critical checkpoint in the activation of the complement system and the innate immune response.
• Describe the different pathways that can lead to the formation of C3 convertase.
  • There are three main pathways that can result in the formation of C3 convertase: the classical, lectin, and alternative pathways. In the classical and lectin pathways, C3 convertase is composed of C4b and C2a, while in the alternative pathway, it is formed by Bb and C3b. Each of these pathways is triggered by different initiating events, such as the binding of antibodies to pathogens (classical) or the recognition of microbial carbohydrates (lectin), but they all converge on the activation of C3 by C3 convertase. The alternative pathway also has the ability to amplify the complement response through a positive feedback loop involving C3 convertase.
• Discuss the importance of the regulation of C3 convertase activity in maintaining immune homeostasis.
  • Tight regulation of C3 convertase activity is essential for maintaining immune homeostasis and preventing excessive or uncontrolled activation of the complement system. Complement regulatory proteins, such as factor H, factor I, and CD55, work to inhibit the formation of C3 convertase or promote its decay, ensuring that the complement response is proportional to the threat and does not cause collateral damage to host cells. Dysregulation of C3 convertase, either through genetic mutations or acquired factors, has been linked to the development of various inflammatory and autoimmune diseases, highlighting the critical role of this enzyme complex in balancing the immune response. Understanding the mechanisms that control C3 convertase activity is therefore crucial for developing targeted therapies to treat complement-mediated disorders.

Related terms

Complement System:

The complement system is a collection of over 30 proteins that work together as part of the innate immune response to detect, mark, and help eliminate pathogens and damaged cells.

C3:

C3 is the central protein in the complement system. When activated by C3 convertase, it is cleaved into C3a and C3b, which go on to trigger further immune responses.

Innate Immune Response: The innate immune response is the body's first line of defense against pathogens, involving mechanisms that are genetically encoded and ready to respond immediately to threats.