Structural highlights
Disease
[CO6_HUMAN] Defects in C6 are the cause of complement component 6 deficiency (C6D) [MIM:612446]. A rare defect of the complement classical pathway associated with susceptibility to severe recurrent infections, predominantly by Neisseria gonorrhoeae or Neisseria meningitidis. [CO7_HUMAN] Immunodeficiency due to a late component of complement deficiency. Disease susceptibility is associated with variations affecting the gene represented in this entry. [CO9_HUMAN] Age-related macular degeneration;Immunodeficiency due to a late component of complements deficiency. Disease susceptibility is associated with variations affecting the gene represented in this entry. Disease susceptibility is associated with variations affecting the gene represented in this entry. [CO8B_HUMAN] Immunodeficiency due to a late component of complements deficiency. Disease susceptibility is associated with variations affecting the gene represented in this entry. [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). [CO8A_HUMAN] Defects in C8A are a cause of complement component 8 deficiency type 1 (C8D1) [MIM:613790]. A rare defect of the complement classical pathway associated with susceptibility to severe recurrent infections, predominantly by Neisseria gonorrhoeae or Neisseria meningitidis.
Function
[CO6_HUMAN] Constituent of the membrane attack complex (MAC) that plays a key role in the innate and adaptive immune response by forming pores in the plasma membrane of target cells. [CO7_HUMAN] Constituent of the membrane attack complex (MAC) that plays a key role in the innate and adaptive immune response by forming pores in the plasma membrane of target cells. C7 serves as a membrane anchor. [CO9_HUMAN] Constituent of the membrane attack complex (MAC) that plays a key role in the innate and adaptive immune response by forming pores in the plasma membrane of target cells. C9 is the pore-forming subunit of the MAC. [CO8B_HUMAN] Constituent of the membrane attack complex (MAC) that plays a key role in the innate and adaptive immune response by forming pores in the plasma membrane of target cells. [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). [CO8G_HUMAN] C8 is a constituent of the membrane attack complex. C8 binds to the C5B-7 complex, forming the C5B-8 complex. C5-B8 binds C9 and acts as a catalyst in the polymerization of C9. The gamma subunit seems to be able to bind retinol. [CO8A_HUMAN] Constituent of the membrane attack complex (MAC) that plays a key role in the innate and adaptive immune response by forming pores in the plasma membrane of target cells. C8A inserts into the target membrane, but does not form pores by itself.[1] [2]
Publication Abstract from PubMed
The membrane attack complex (MAC) is one of the immune system's first responders. Complement proteins assemble on target membranes to form pores that lyse pathogens and impact tissue homeostasis of self-cells. How MAC disrupts the membrane barrier remains unclear. Here we use electron cryo-microscopy and flicker spectroscopy to show that MAC interacts with lipid bilayers in two distinct ways. Whereas C6 and C7 associate with the outer leaflet and reduce the energy for membrane bending, C8 and C9 traverse the bilayer increasing membrane rigidity. CryoEM reconstructions reveal plasticity of the MAC pore and demonstrate how C5b6 acts as a platform, directing assembly of a giant beta-barrel whose structure is supported by a glycan scaffold. Our work provides a structural basis for understanding how beta-pore forming proteins breach the membrane and reveals a mechanism for how MAC kills pathogens and regulates cell functions.
CryoEM reveals how the complement membrane attack complex ruptures lipid bilayers.,Menny A, Serna M, Boyd CM, Gardner S, Joseph AP, Morgan BP, Topf M, Brooks NJ, Bubeck D Nat Commun. 2018 Dec 14;9(1):5316. doi: 10.1038/s41467-018-07653-5. PMID:30552328[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Steckel EW, York RG, Monahan JB, Sodetz JM. The eighth component of human complement. Purification and physicochemical characterization of its unusual subunit structure. J Biol Chem. 1980 Dec 25;255(24):11997-2005. PMID:7440581
- ↑ Hadders MA, Beringer DX, Gros P. Structure of C8alpha-MACPF reveals mechanism of membrane attack in complement immune defense. Science. 2007 Sep 14;317(5844):1552-4. PMID:17872444 doi:317/5844/1552
- ↑ Menny A, Serna M, Boyd CM, Gardner S, Joseph AP, Morgan BP, Topf M, Brooks NJ, Bubeck D. CryoEM reveals how the complement membrane attack complex ruptures lipid bilayers. Nat Commun. 2018 Dec 14;9(1):5316. doi: 10.1038/s41467-018-07653-5. PMID:30552328 doi:http://dx.doi.org/10.1038/s41467-018-07653-5
