Complement Component Factor B/CFB

Introduction of Complement Component Factor B/CFB

Complement Factor B, also known as CFB, is a single-chain, 93-kDa polypeptide. It is part of the alternate pathway of the complement system and circulates in the blood as a single chain polypeptide. CFB exists in human serum in an inactive zymogen conformation, which itself consists of a three-complement control protein (CCP) domain, a von Willebrand factor type A (vWFA) module, and a serine protease domain (Fig.1). After binding to C3b, CFB is recognized by factor D and hydrolyzed between its CCP and vWFA domains by factor D, leading to the formation of the heterodimer complex C3bBb, the C3 convertase of the complement alternative pathway.

Schematic representation of factor B showing components CCP1–3 (three-complement control proteins), vWFA (von Willebrand factor type A), and SP (serine protease).

Fig.1 Schematic representation of factor B showing components CCP1–3 (three-complement control proteins), vWFA (von Willebrand factor type A), and SP (serine protease). (Le, 2007)

When the alternative pathway is activated, CFB is cleaved by complement factor D yielding the noncatalytic chain Ba (30 kDa) and the catalytic subunit Bb (63 kDa). They represent separate domains within CFB, Ba being the N-terminal part of the molecule. In the presence of C3b, the site of cleavage of CFB by factor D is an Arg234↓Lys 235 bond at a site containing three basic residues. The active subunit Bb is a serine protease which combines with complement factor 3b to form the alternative pathway complement factors C3 or C5 convertase. In addition, Bb is also involved in proliferation and differentiation of preactivated B-lymphocytes, rapid spreading of peripheral blood monocytes, stimulation of lymphocyte blastogenesis and lysis of erythrocytes, while Ba inhibits the proliferation of preactivated B-lymphocytes.

CFB-related Disease

  1. CFB deficiency

CFB deficiency is the cause of susceptibility to hemolytic uremic syndrome atypical type 4 (aHUS4). It is a complex hereditary disease characterized by microangiopathic hemolytic anemia, thrombocytopenia and renal failure. In contrast to the typical hemolytic uremic syndrome, atypical forms have a worse prognosis, higher mortality rates, and often progress to end-stage renal disease. Susceptibility to the development of atypical hemolytic uremic syndrome (aHUS) can be conferred by mutations in multiple complement components or regulatory factors in the complement cascade system.

  1. CFB and other disease

Studies have found that CFB in adipose tissue and serum is elevated in patients with type 2 diabetes mellitus and cardiovascular disease, but the causal relationship with the pathogenesis of the disease is unknown. CFB content is also elevated in adipose tissue and serum of the spontaneously hypertensive rat, which is a typical model of metabolic syndrome. These results indicate that CFB plays an important role in the development of spontaneously hypertensive rat metabolic syndrome phenotypes and related traits of metabolic syndrome in humans and that CFB may be a potential target for the treatment of cardiac metabolic diseases.

Creative Biolabs offers a full range of complement component CFB-related services and products, including:

  1. CFB Antibodies
  2. CFB Related Array Kits
  3. CFB Related Peptides
  4. CFB Related Lysates

If you want more information, please feel free to contact us.

Reference

  1. Le, G. T.; et al. Profiling the enzymatic properties and inhibition of human complement factor B. Journal of Biological Chemistry. 2007, 282(48): 34809-34816.

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