6i2x

Structural highlights

Disease

[CO5_HUMAN] Defects in C5 are the cause of complement component 5 deficiency (C5D) [MIM:609536]. A rare defect of the complement classical pathway associated with susceptibility to severe recurrent infections, predominantly by Neisseria gonorrhoeae or Neisseria meningitidis. Note=An association study of C5 haplotypes and genotypes in individuals with chronic hepatitis C virus infection shows that individuals homozygous for the C5_1 haplotype have a significantly higher stage of liver fibrosis than individuals carrying at least 1 other allele (PubMed:15995705).

Function

[CO5_HUMAN] Activation of C5 by a C5 convertase initiates the spontaneous assembly of the late complement components, C5-C9, into the membrane attack complex. C5b has a transient binding site for C6. The C5b-C6 complex is the foundation upon which the lytic complex is assembled. Derived from proteolytic degradation of complement C5, C5 anaphylatoxin is a mediator of local inflammatory process. It induces the contraction of smooth muscle, increases vascular permeability and causes histamine release from mast cells and basophilic leukocytes. C5a also stimulates the locomotion of polymorphonuclear leukocytes (chemokinesis) and direct their migration toward sites of inflammation (chemotaxis). [VCO3_NAJKA] Complement-activating protein in cobra venom. It is a structural and functional analog of complement component C3b, the activated form of C3. It binds factor B (CFB), which is subsequently cleaved by factor D (CFD) to form the bimolecular complex CVF/Bb. CVF/Bb is a C3/C5 convertase that cleaves both complement components C3 and C5. Structurally, it resembles the C3b degradation product C3c, which is not able to form a C3/C5 convertase. Unlike C3b/Bb, CVF/Bb is a stable complex and completely resistant to the actions of complement regulatory factors H (CFH) and I (CFI). Therefore, CVF continuously activates complement resulting in the depletion of complement activity.

References

1. ↑ Jendza K, Kato M, Salcius M, Srinivas H, De Erkenez A, Nguyen A, McLaughlin D, Be C, Wiesmann C, Murphy J, Bolduc P, Mogi M, Duca J, Namil A, Capparelli M, Darsigny V, Meredith E, Tichkule R, Ferrara L, Heyder J, Liu F, Horton PA, Romanowski MJ, Schirle M, Mainolfi N, Anderson K, Michaud GA. A small-molecule inhibitor of C5 complement protein. Nat Chem Biol. 2019 Jul;15(7):666-668. doi: 10.1038/s41589-019-0303-9. Epub 2019 , Jun 17. PMID:31209353 doi:http://dx.doi.org/10.1038/s41589-019-0303-9