* Complement scientists have decided to designate the smaller of all C fragments with an ‘a’, and the larger with a ‘b’ and hence more recent literature may refer the larger C2 fragment as C2b. Complement Technology, Inc. uses the current Uniprot names which follow the original naming practice.
The smaller fragment of complement protein C2 is C2b that results from the activation of the classical and lectin pathways. CompTech prepares the C2b fragment from complement protein C2 which was purified from normal human serum. Initiation of classical and lectin pathway generates proteolytic enzyme complexes which are bound to the target surface (C1q/C1r/C1s in the classical pathway and MBL/ Ficolin/ MASPs in the lectin pathway). C1s and MASP in these complexes activate both C4 and C2. They cleave a peptide bond in C4 depositing C4b on the surface. They also cleave C2 into two fragments, the larger catalytic fragment C2a (73 kDa) binds to C4b and forms the C3/C5 convertase enzyme complex C4b,C2a and the smaller fragment C2b (34 kDa) is released in the fluid phase (Rawal N. and Pangburn M.K. 2003 and Nagasawa S. & Stroud, R. M. 1977). The smaller C2b fragment comes from the N-terminal of C2 protein, and it contains three CCP domains which interact weakly with C4b (Krishnan V. et al., 2009). Although the functional role of the released C2b fragment is not clearly known, one study has suggested that the C-terminal region of the C2b fragment increases vascular permeability in humans and guinea pigs (Strang et al., 1988).
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