7xt3
Crystal Structure of Hepatitis virus A 2C protein 128-335 aaCrystal Structure of Hepatitis virus A 2C protein 128-335 aa
Structural highlights
FunctionPOLG_HAVHM Capsid proteins VP1, VP2, and VP3 form a closed capsid enclosing the viral positive strand RNA genome. All these proteins contain a beta-sheet structure called beta-barrel jelly roll. Together they form an icosahedral capsid (T=3) composed of 60 copies of each VP1, VP2, and VP3, with a diameter of approximately 300 Angstroms. VP1 is situated at the 12 fivefold axes, whereas VP2 and VP3 are located at the quasi-sixfold axes. The capsid interacts with HAVCR1 to provide virion attachment to target cell (By similarity). Protein VP0: VP0 precursor is a component of immature procapsids. The N-terminal domain of VP0, protein VP4, is needed for the assembly of 12 pentamers into the icosahedral structure. Unlike other picornaviruses, HAV VP4 does not seem to be myristoylated and has not been detected in mature virions, supposedly owing to its small size. VP1-2A precursor is a component of immature procapsids and corresponds to an extended form of the structural protein VP1. The C-terminal domain of VP1-2A, protein 2A, acts as an assembly signal that allows pentamerization of P1-2A, which is the precursor of the structural proteins. 2A is proteolytically removed from particulate VP1-2A by a host protease and does not seem to be found in mature particles. Protein 2B and 2BC precursor affect membrane integrity and cause an increase in membrane permeability. Protein 2C: Associates with and induces structural rearrangements of intracellular membranes. It displays RNA-binding, nucleotide binding and NTPase activities (By similarity). Protein 3A, via its hydrophobic domain, serves as membrane anchor to the 3AB and 3ABC precursors. The 3AB precursor interacts with the 3CD precursor and with RNA structures found at both the 5'- and 3'-termini of the viral genome. Since the 3AB precursor contains the hydrophobic domain 3A, it probably anchors the whole viral replicase complex to intracellular membranes on which viral RNA synthesis occurs. The 3ABC precursor is targeted to the mitochondrial membrane where protease 3C activity cleaves and inhibits the host antiviral protein MAVS, thereby disrupting activation of IRF3 through the IFIH1/MDA5 pathway. In vivo, the protease activity of 3ABC precursor is more efficient in cleaving the 2BC precursor than that of protein 3C. The 3ABC precursor may therefore play a role in the proteolytic processing of the polyprotein. Protein 3B is covalently linked to the 5'-end of both the positive-strand and negative-strand genomic RNAs. It acts as a genome-linked replication primer. Protease 3C: cysteine protease that generates mature viral proteins from the precursor polyprotein. In addition to its proteolytic activity, it binds to viral RNA, and thus influences viral genome replication. RNA and substrate bind cooperatively to the protease. Also cleaves host proteins such as PCBP2. RNA-directed RNA polymerase 3D-POL replicates genomic and antigenomic RNA by recognizing replications specific signals. Publication Abstract from PubMedThe HAV nonstructural protein 2C is essential for virus replication; however, its precise function remains elusive. Although HAV 2C shares 24-27% sequence identity with other 2Cs, key motifs are conserved. Here, we demonstrate that HAV 2C is an ATPase but lacking helicase activity. We identified an ATPase-independent nuclease activity of HAV 2C with a preference for polyuridylic single-stranded RNAs. We determined the crystal structure of an HAV 2C fragment to 2.2 A resolution, containing an ATPase domain, a region equivalent to enterovirus 2C zinc-finger (ZFER) and a C-terminal amphipathic helix (PBD). The PBD of HAV 2C occupies a hydrophobic pocket (Pocket) in the adjacent 2C, and we show the PBD-Pocket interaction is vital for 2C functions. We identified acidic residues that are essential for the ribonuclease activity and demonstrated mutations at these sites abrogate virus replication. We built a hexameric-ring model of HAV 2C, revealing the ribonuclease-essential residues clustering around the central pore of the ring, whereas the ATPase active sites line up at the gaps between adjacent 2Cs. Finally, we show the ribonuclease activity is shared by other picornavirus 2Cs. Our findings identified a previously unfound activity of picornavirus 2C, providing novel insights into the mechanisms of virus replication. Biochemical and structural characterization of hepatitis A virus 2C reveals an unusual ribonuclease activity on single-stranded RNA.,Chen P, Wojdyla JA, Colasanti O, Li Z, Qin B, Wang M, Lohmann V, Cui S Nucleic Acids Res. 2022 Sep 9;50(16):9470-9489. doi: 10.1093/nar/gkac671. PMID:35947700[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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