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After cleavage and binding to cell surface, the C3b fragment is ready to bind a plasma protein called Factor B. The Factor B (a zymogen) is cleaved by a plasma serine protease Factor D releasing a small fragment called Ba and generating a larger fragment called Bb that remains attached to C3b. Also Mg2+ ions are necessary for forming a ...
C3b is potent in opsonization: tagging pathogens, immune complexes (antigen-antibody), and apoptotic cells for phagocytosis. Additionally, C3b plays a role in forming a C3 convertase when bound to Factor B (C3bBb complex), or a C5 convertase when bound to C4b and C2b (C4b2b3b complex) or when an additional C3b molecule binds to the C3bBb ...
This convertase, the alternative pathway C3-convertase, although only produced in small amounts, can cleave multiple C3 proteins into C3a and C3b. The complex is believed to be unstable until it binds properdin, a serum protein. The addition of properdin forms the complex C3bBbP, a stable compound which can bind an additional C3b to form ...
Therapies that utilize classical complement activation have been shown to be effective in targeting and killing cancer cells and destroying tumors. [11] Tachyplesin, a small peptide, has been shown to exhibit these effects. When injected into target tissue encourages recruitment of C1q and activates downstream events, eventually leading to the ...
12266 Ensembl ENSG00000125730 ENSMUSG00000024164 UniProt P01024 P01027 RefSeq (mRNA) NM_000064 NM_009778 RefSeq (protein) NP_000055 NP_033908 Location (UCSC) Chr 19: 6.68 – 6.73 Mb Chr 17: 57.51 – 57.54 Mb PubMed search Wikidata View/Edit Human View/Edit Mouse Complement component 3, often simply called C3, is a protein of the immune system that is found primarily in the blood. It plays a ...
Cell-bound C3 and C5 convertase differ in their C3b requirement. C3-convertase (C3bBb) need only one molecule of C3b to form, whereas two or more C3b are required for generation of C5 convertase (C3bBb). It means, when C3b is randomly distributed on the surface of a cell, only C3 convertase activity appears after addition of Factors B and D.
Interaction of DAF with cell-associated C4b of the classical and lectin pathways interferes with the conversion of C2 to C2b, thereby preventing formation of the C4b2a C3-convertase, and interaction of DAF with C3b of the alternative pathway interferes with the conversion of factor B to Bb by factor D, thereby preventing formation of the C3bBb ...
The active subunit Bb is a serine protease that associates with C3b to form the alternative pathway C3 convertase. Bb is involved in the proliferation of preactivated B lymphocytes, while Ba inhibits their proliferation. This gene localizes to the major histocompatibility complex (MHC class III) region on chromosome 6. This cluster includes ...