Structural highlights
Disease
[CO2_HUMAN] Defects in C2 are the cause of complement component 2 deficiency (C2D) [MIM:217000]. A deficiency of the complement classical pathway associated with the development of autoimmune disorders, mainly systemic lupus erythematosus. Skin and joint manifestations are common and renal disease is relatively rare. Patients with complement component 2 deficiency are also reported to have recurrent or invasive infections.[1] [2]
Function
[CO2_HUMAN] Component C2 which is part of the classical pathway of the complement system is cleaved by activated factor C1 into two fragments: C2b and C2a. C2a, a serine protease, then combines with complement factor 4b to generate the C3 or C5 convertase.
Evolutionary Conservation
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Publication Abstract from PubMed
The multi-domain serine protease C2 provides the catalytic activity for the C3 and C5- convertases of the classical and lectin pathways of complement activation. Formation of these convertases requires the Mg(2+)-dependent binding of C2 to C4b, and the subsequent cleavage of C2 by C1s or MASP2, respectively. The C-terminal fragment C2a consisting of a serine protease (SP) and a von Willebrand factor type A (vWFA) domain, remains attached to C4b, forming the C3 convertase, C4b2a. Here, we present the crystal structure of Mg(2+)-bound C2a to 1.9 A resolution in comparison to its homolog Bb, the catalytic subunit of the alternative pathway C3 convertase, C3bBb. Although the overall domain arrangement of C2a is similar to Bb, there are certain structural differences. Unexpectedly, the conformation of the metal ion-dependent adhesion site and the position of the alpha7 helix of the vWFA domain indicate a co-factor-bound or open conformation. The active site of the SP domain is in a zymogen-like inactive conformation. On the basis of these structural features, we suggest a model for the initial steps of C3 convertase assembly.
The crystal structure of C2a, the catalytic fragment of classical pathway C3 and C5 convertase of human complement.,Krishnan V, Xu Y, Macon K, Volanakis JE, Narayana SV J Mol Biol. 2007 Mar 16;367(1):224-33. Epub 2006 Dec 19. PMID:17234210[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Wetsel RA, Kulics J, Lokki ML, Kiepiela P, Akama H, Johnson CA, Densen P, Colten HR. Type II human complement C2 deficiency. Allele-specific amino acid substitutions (Ser189 --> Phe; Gly444 --> Arg) cause impaired C2 secretion. J Biol Chem. 1996 Mar 8;271(10):5824-31. PMID:8621452
- ↑ Zhu ZB, Atkinson TP, Volanakis JE. A novel type II complement C2 deficiency allele in an African-American family. J Immunol. 1998 Jul 15;161(2):578-84. PMID:9670930
- ↑ Krishnan V, Xu Y, Macon K, Volanakis JE, Narayana SV. The crystal structure of C2a, the catalytic fragment of classical pathway C3 and C5 convertase of human complement. J Mol Biol. 2007 Mar 16;367(1):224-33. Epub 2006 Dec 19. PMID:17234210 doi:10.1016/j.jmb.2006.12.039
