What is the role of C3 convertase?
What is the role of C3 convertase?
The C4b2a complex, or C3 convertase, catalyzes the cleavage of C3 into C3a and C3b. This is the most important step in the complement cascade and occurs in the classic, alternative, and MBL pathways. C3b is a highly unstable molecule that has a unique thioester that allows covalent binding to a microbial cell.
What is Properdin system?
The properdin system is responsible for the bactericidal action of normal human serum against a variety of microorganisms. The present work shows that the removal of properdin from serum also removes bactericidal activity. Addition of properdin to properdin-deficient serum restores bactericidal activity.
What is C4b2a3b?
Attachment of activated C3b fragment to C3 convertase (C4b2a) generates a trimolecular complex C4b2a3b, which changes substrate specificity and becomes C5 convertase. The proteolytic activity of C3 and C5 convertase is restricted to single peptide bonds in C3 and C5, respectively.
What does C5 convertase do?
C5 convertase is an enzyme belonging to a family of serine proteases that play key role in the innate immunity. It participates in the complement system ending with cell death. There are four different C5 convertases able to specifically convert the protein C5 to C5a and C5b fragments.
Which serum protein stabilizes the C3 convertase in alternative pathway?
C4-NeF
C4-NeF stabilizes the classical pathway C3 convertase (C4b2a) and leads to C3 consumption in a fashion analogous to C3-NeF. We report an 18-year-old patient with C3 deficiency who presented with a systemic Neisseria meningitidis infection.
What can properdin be activated by?
The properdin complement pathway is initiated as a result of spontaneous hydrolysis of the C3 component of complement in serum. This produces a cleavage product, C3b, that binds to microbial surfaces, forming an enzyme, C3 convertase, which initiates the activation of the subsequent complement components (Figure 12.1).
What clinical condition is associated with Properdin deficiency?
Properdin deficiency is a rare X-linked disease in which properdin, an important complement factor responsible for the stabilization of the alternative C3 convertase, is deficient. Affected individuals are susceptible to fulminant meningococcal disease.
What is the function of C5a?
C5a is a strong chemoattractant and is involved in the recruitment of inflammatory cells such as neutrophils, eosinophils, monocytes, and T lymphocytes, in activation of phagocytic cells and release of granule-based enzymes and generation of oxidants, all of which may contribute to innate immune functions or tissue …
What do Anaphylatoxins do?
The C3a, C4a and C5a components are referred to as anaphylatoxins: they cause smooth muscle contraction, vasodilation, histamine release from mast cells, and enhanced vascular permeability. They also mediate chemotaxis, inflammation, and generation of cytotoxic oxygen radicals.
What is the C5 convertase in the alternative pathway?
C5 convertase of the alternative C pathway is a complex enzyme consisting of three C fragments–one molecule of a major fragment of factor B (Bb) and two molecules of a major fragment of C3 (C3b). Based on this evidence, a new model of the alternative pathway C5 convertase is proposed.
