CFB-b Human
Description
Functional Role in the Complement System
Bb’s primary role is as a subunit of the C3 convertase (C3bBb), which amplifies complement activation by cleaving C3 into C3a (anaphylatoxin) and C3b (opsonin) . Subsequent binding of a second C3b molecule converts the C3 convertase into the C5 convertase (C3bBbC3b), initiating terminal pathway activation and membrane attack complex (MAC) formation .
Critical Steps Involving Bb:
Clinical and Pathological Implications
Dysregulation of Bb activity is linked to autoimmune, inflammatory, and metabolic disorders.
Disease Associations:
Metabolic Syndrome: CFB/Bb is implicated in adipose tissue dysfunction. In spontaneously hypertensive rats, Cfb knockout reduced blood pressure, improved glucose tolerance, and redistributed fat from visceral to subcutaneous depots . Human GWAS data link CFB variants to visceral fat, hypertension, and triglycerides .
Targeting Bb in Disease
Rheumatoid Arthritis (RA): Bb is elevated in RA synovial fluid. siRNA targeting CFB reduced immune cell infiltration and joint damage in murine models .
Genetic and Epigenetic Insights
Diagnostic and Analytical Methods
Limitations: Direct Bb measurement is challenging; most assays infer activity via CFB levels or pathway function.
References
Product Specs
Complement factor B (EC:3.4.21.47), C3/C5 convertase, Glycine-rich beta glycoprotein, GBG, PBF2, Properdin factor B, Complement factor B Ba fragment, Complement factor B Bb fragment, CFB, Complement Factor B, BFD, AHUS4, BF, BFD, CFAB, FB, FBI12, H2-Bf.
Human Plasma.
Product Science Overview
Complement Factor B is a glycosylated protein composed of a single polypeptide chain with a molecular weight of approximately 93,000 Da . It is found in plasma at a concentration of around 200 µg/mL . Upon activation by Factor D, Complement Factor B is cleaved into two fragments: Ba and Bb . The Bb fragment, which is the focus of this article, is a serine protease with a molecular weight of approximately 60,000 Da .
The Bb fragment is essential for the formation of the C3 and C5 convertases, which are crucial for the activation of the complement system . Specifically, Bb combines with Complement Factor 3b (C3b) to form the C3b,Bb complex, which acts as a C3 convertase. This complex can further bind another C3b molecule to form the C5 convertase, which is responsible for cleaving C5 into C5a and C5b .
The Bb fragment has been implicated in various biological activities, including:
- Proliferation and Differentiation of B-Lymphocytes: Bb has been shown to stimulate the proliferation and differentiation of preactivated B-lymphocytes .
- Monocyte Activation: Bb promotes the rapid spreading of peripheral blood monocytes .
- Lymphocyte Blastogenesis: Bb stimulates lymphocyte blastogenesis, which is the process of lymphocyte activation and proliferation .
- Erythrocyte Lysis: Bb can induce the lysis of erythrocytes .
Complement Factor B and its fragments are typically purified from normal human serum. The purification process involves several steps to ensure the protein’s integrity and activity. Factor B is first isolated from the serum, and then it is activated by Factor D to produce the Ba and Bb fragments . The Bb fragment is then further purified to remove any contaminants and ensure its purity .
Deficiencies or dysregulations in Complement Factor B can lead to various immunological disorders. For example, Complement Factor B deficiency (CFBD) is characterized by increased susceptibility to bacterial infections, particularly Neisseria infections . This condition arises due to a defect in the alternative complement pathway, which impairs the body’s ability to effectively clear pathogens .
