View source for 8ovb


==Human Complement C3b in complex with Trypanosoma brucei ISG65.==
<StructureSection load='8ovb' size='340' side='right'caption='[[8ovb]], [[Resolution|resolution]] 3.40&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[8ovb]] is a 3 chain structure with sequence from [https://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens] and [https://en.wikipedia.org/wiki/Trypanosoma_brucei_brucei Trypanosoma brucei brucei]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=8OVB OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=8OVB FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">Electron Microscopy, [[Resolution|Resolution]] 3.4&#8491;</td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=8ovb FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=8ovb OCA], [https://pdbe.org/8ovb PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=8ovb RCSB], [https://www.ebi.ac.uk/pdbsum/8ovb PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=8ovb ProSAT]</span></td></tr>
</table>
== Disease ==
[https://www.uniprot.org/uniprot/CO3_HUMAN CO3_HUMAN] Defects in C3 are the cause of complement component 3 deficiency (C3D) [MIM:[https://omim.org/entry/613779 613779]. A rare defect of the complement classical pathway. Patients develop recurrent, severe, pyogenic infections because of ineffective opsonization of pathogens. Some patients may also develop autoimmune disorders, such as arthralgia and vasculitic rashes, lupus-like syndrome and membranoproliferative glomerulonephritis.<ref>PMID:19913840</ref> <ref>PMID:9596584</ref> <ref>PMID:11387479</ref> <ref>PMID:15713468</ref> <ref>PMID:7961791</ref> [:]  Genetic variation in C3 is associated with susceptibility to age-related macular degeneration type 9 (ARMD9) [MIM:[https://omim.org/entry/611378 611378]. ARMD is a multifactorial eye disease and the most common cause of irreversible vision loss in the developed world. In most patients, the disease is manifest as ophthalmoscopically visible yellowish accumulations of protein and lipid that lie beneath the retinal pigment epithelium and within an elastin-containing structure known as Bruch membrane.<ref>PMID:19913840</ref> <ref>PMID:17634448</ref>   Defects in C3 are a cause of susceptibility to hemolytic uremic syndrome atypical type 5 (AHUS5) [MIM:[https://omim.org/entry/612925 612925]. An atypical form of hemolytic uremic syndrome. It is a complex genetic disease characterized by microangiopathic hemolytic anemia, thrombocytopenia, renal failure and absence of episodes of enterocolitis and diarrhea. In contrast to typical hemolytic uremic syndrome, atypical forms have a poorer prognosis, with higher death rates and frequent progression to end-stage renal disease. Note=Susceptibility to the development of atypical hemolytic uremic syndrome can be conferred by mutations in various components of or regulatory factors in the complement cascade system. Other genes may play a role in modifying the phenotype.<ref>PMID:19913840</ref> <ref>PMID:18796626</ref> <ref>PMID:20513133</ref>   Note=Increased levels of C3 and its cleavage product ASP, are associated with obesity, diabetes and coronary heart disease. Short-term endurance training reduces baseline ASP levels and subsequently fat storage.<ref>PMID:19913840</ref> 
== Function ==
[https://www.uniprot.org/uniprot/CO3_HUMAN CO3_HUMAN] C3 plays a central role in the activation of the complement system. Its processing by C3 convertase is the central reaction in both classical and alternative complement pathways. After activation C3b can bind covalently, via its reactive thioester, to cell surface carbohydrates or immune aggregates.<ref>PMID:8376604</ref> <ref>PMID:2909530</ref> <ref>PMID:9059512</ref> <ref>PMID:9555951</ref> <ref>PMID:10432298</ref> <ref>PMID:15833747</ref> <ref>PMID:16333141</ref> <ref>PMID:19615750</ref>   Derived from proteolytic degradation of complement C3, C3a 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.<ref>PMID:8376604</ref> <ref>PMID:2909530</ref> <ref>PMID:9059512</ref> <ref>PMID:9555951</ref> <ref>PMID:10432298</ref> <ref>PMID:15833747</ref> <ref>PMID:16333141</ref> <ref>PMID:19615750</ref>   Acylation stimulating protein (ASP): adipogenic hormone that stimulates triglyceride (TG) synthesis and glucose transport in adipocytes, regulating fat storage and playing a role in postprandial TG clearance. Appears to stimulate TG synthesis via activation of the PLC, MAPK and AKT signaling pathways. Ligand for GPR77. Promotes the phosphorylation, ARRB2-mediated internalization and recycling of GPR77.<ref>PMID:8376604</ref> <ref>PMID:2909530</ref> <ref>PMID:9059512</ref> <ref>PMID:9555951</ref> <ref>PMID:10432298</ref> <ref>PMID:15833747</ref> <ref>PMID:16333141</ref> <ref>PMID:19615750</ref> 
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
African trypanosomes replicate within infected mammals where they are exposed to the complement system. This system centres around complement C3, which is present in a soluble form in serum but becomes covalently deposited onto the surfaces of pathogens after proteolytic cleavage to C3b. Membrane-associated C3b triggers different complement-mediated effectors which promote pathogen clearance. To counter complement-mediated clearance, African trypanosomes have a cell surface receptor, ISG65, which binds to C3b and which decreases the rate of trypanosome clearance in an infection model. However, the mechanism by which ISG65 reduces C3b function has not been determined. We reveal through cryogenic electron microscopy that ISG65 has two distinct binding sites for C3b, only one of which is available in C3 and C3d. We show that ISG65 does not block the formation of C3b or the function of the C3 convertase which catalyses the surface deposition of C3b. However, we show that ISG65 forms a specific conjugate with C3b, perhaps acting as a decoy. ISG65 also occludes the binding sites for complement receptors 2 and 3, which may disrupt recruitment of immune cells, including B cells, phagocytes, and granulocytes. This suggests that ISG65 protects trypanosomes by combining multiple approaches to dampen the complement cascade.

Molecular mechanism of complement inhibition by the trypanosome receptor ISG65.,Cook AD, Carrington M, Higgins MK Elife. 2024 Apr 24;12:RP88960. doi: 10.7554/eLife.88960. PMID:38655765<ref>PMID:38655765</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 8ovb" style="background-color:#fffaf0;"></div>
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Trypanosoma brucei brucei]]
[[Category: Cook AD]]
[[Category: Higgins MK]]