6nk6

Structural highlights

Function

[POLS_CHIK3] Capsid protein possesses a protease activity that results in its autocatalytic cleavage from the nascent structural protein. Following its self-cleavage, the capsid protein transiently associates with ribosomes, and within several minutes the protein binds to viral RNA and rapidly assembles into icosaedric core particles. The resulting nucleocapsid eventually associates with the cytoplasmic domain of E2 at the cell membrane, leading to budding and formation of mature virions. New virions attach to target cells, and after endocytosis their membrane fuses with the target cell membrane. This leads to the release of the nucleocapsid into the cytoplasm, followed by an uncoating event necessary for the genomic RNA to become accessible. The uncoating might be triggered by the interaction of capsid proteins with ribosomes. Binding of ribosomes would release the genomic RNA since the same region is genomic RNA-binding and ribosome-binding (By similarity). E3 protein's function is unknown (By similarity). E2 is responsible for viral attachment to target host cell, by binding to the cell receptor. Synthesized as a p62 precursor which is processed by furin at the cell membrane just before virion budding, giving rise to E2-E1 heterodimer. The p62-E1 heterodimer is stable, whereas E2-E1 is unstable and dissociate at low pH. p62 is processed at the last step, presumably to avoid E1 fusion activation before its final export to cell surface. E2 C-terminus contains a transitory transmembrane that would be disrupted by palmitoylation, resulting in reorientation of the C-terminal tail from lumenal to cytoplasmic side. This step is critical since E2 C-terminus is involved in budding by interacting with capsid proteins. This release of E2 C-terminus in cytoplasm occurs lately in protein export, and precludes premature assembly of particles at the endoplasmic reticulum membrane (By similarity). 6K is a constitutive membrane protein involved in virus glycoprotein processing, cell permeabilization, and the budding of viral particles. Disrupts the calcium homeostasis of the cell, probably at the endoplasmic reticulum level. This leads to cytoplasmic calcium elevation. Because of its lipophilic properties, the 6K protein is postulated to influence the selection of lipids that interact with the transmembrane domains of the glycoproteins, which, in turn, affects the deformability of the bilayer required for the extreme curvature that occurs as budding proceeds. Present in low amount in virions, about 3% compared to viral glycoproteins (By similarity). E1 is a class II viral fusion protein. Fusion activity is inactive as long as E1 is bound to E2 in mature virion. After virus attachment to target cell and endocytosis, acidification of the endosome would induce dissociation of E1/E2 heterodimer and concomitant trimerization of the E1 subunits. This E1 trimer is fusion active, and promotes release of viral nucleocapsid in cytoplasm after endosome and viral membrane fusion. Efficient fusion requires the presence of cholesterol and sphingolipid in the target membrane (By similarity). [MXRA8_MOUSE] Transmembrane protein which can modulate activity of various signaling pathways, probably via binding to integrin ITGAV:ITGB3 (PubMed:18366072, PubMed:22492581, PubMed:29702220). Mediates heterophilic cell-cell interactions in vitro (PubMed:18366072). Inhibits osteoclastogenesis downstream of TNFSF11/RANKL and CSF1, where it may function by attenuating signaling via integrin ITGB3 and MAP kinase p38 (PubMed:22492581). Plays a role in cartilage formation where it promotes proliferation and maturation of growth plate chondrocytes (PubMed:29702220). Stimulates formation of primary cilia in chondrocytes (PubMed:29702220). Enhances expression of genes involved in the hedgehog signaling pathway in chondrocytes, including the hedgehog signaling molecule IHH; may also promote signaling via the PTHLH/PTHrP pathway (PubMed:29702220). Plays a role in angiogenesis where it suppresses migration of endothelial cells and also promotes their apoptosis (By similarity). Inhibits VEGF-induced activation of AKT and p38 MAP kinase in endothelial cells (By similarity). Also inhibits VTN (vitronectin)-mediated integrin ITGAV:ITGB3 signaling and activation of PTK2/FAK (By similarity). May play a role in the maturation and maintenance of the blood-brain barrier (PubMed:14603461).[UniProtKB:Q9BRK3]^{[1] [2] [3] [4]}

References

1. ↑ Yonezawa T, Ohtsuka A, Yoshitaka T, Hirano S, Nomoto H, Yamamoto K, Ninomiya Y. Limitrin, a novel immunoglobulin superfamily protein localized to glia limitans formed by astrocyte endfeet. Glia. 2003 Dec;44(3):190-204. PMID:14603461 doi:http://dx.doi.org/10.1002/glia.10279
2. ↑ Jung YK, Jin JS, Jeong JH, Kim HN, Park NR, Choi JY. DICAM, a novel dual immunoglobulin domain containing cell adhesion molecule interacts with alphavbeta3 integrin. J Cell Physiol. 2008 Sep;216(3):603-14. doi: 10.1002/jcp.21438. PMID:18366072 doi:http://dx.doi.org/10.1002/jcp.21438
3. ↑ Jung YK, Han SW, Kim GW, Jeong JH, Kim HJ, Choi JY. DICAM inhibits osteoclast differentiation through attenuation of the integrin alphaVbeta3 pathway. J Bone Miner Res. 2012 Sep;27(9):2024-34. doi: 10.1002/jbmr.1632. PMID:22492581 doi:http://dx.doi.org/10.1002/jbmr.1632
4. ↑ Han S, Park HR, Lee EJ, Jang JA, Han MS, Kim GW, Jeong JH, Choi JY, Beier F, Jung YK. Dicam promotes proliferation and maturation of chondrocyte through Indian hedgehog signaling in primary cilia. Osteoarthritis Cartilage. 2018 Jul;26(7):945-953. doi:, 10.1016/j.joca.2018.04.008. Epub 2018 Apr 25. PMID:29702220 doi:http://dx.doi.org/10.1016/j.joca.2018.04.008
5. ↑ Basore K, Kim AS, Nelson CA, Zhang R, Smith BK, Uranga C, Vang L, Cheng M, Gross ML, Smith J, Diamond MS, Fremont DH. Cryo-EM Structure of Chikungunya Virus in Complex with the Mxra8 Receptor. Cell. 2019 May 6. pii: S0092-8674(19)30392-7. doi: 10.1016/j.cell.2019.04.006. PMID:31080061 doi:http://dx.doi.org/10.1016/j.cell.2019.04.006