Structural highlights
Function
[POLG_CXA9] Capsid proteins VP1, VP2, VP3 and VP4 form a closed capsid enclosing the viral positive strand RNA genome. VP4 lies on the inner surface of the protein shell formed by VP1, VP2 and VP3. All the three latter 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 (By similarity). Capsid proteins interact with host alpha-V/beta-6 integrin heterodimer to provide virion attachment target cell. VP0 precursor is a component of immature procapsids (By similarity). Protein 2A is a cysteine protease that is responsible for the cleavage between the P1 and P2 regions. It cleaves the host translation initiation factor EIF4G1, in order to shut down the capped cellular mRNA transcription (By similarity). Protein 2B affects membrane integrity and cause an increase in membrane permeability (By similarity). 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. It also inhibits endoplasmic reticulum-to-Golgi transport (By similarity). Protein 3C is a 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 co-operatively to the protease (By similarity). RNA-directed RNA polymerase 3D-POL replicates genomic and antigenomic RNA by recognizing replications specific signals (By similarity).
Publication Abstract from PubMed
Coxsackievirus A9 (CVA9) is an important pathogen of the Picornaviridae family. It utilizes cellular receptors from the integrin alphav family for binding to its host cells prior to entry and genome release. Among the integrins tested, it has the highest affinity for alphavbeta6, which recognizes the arginine-glycine-aspartic acid (RGD) loop present on the C terminus of viral capsid protein, VP1. As the atomic model of CVA9 lacks the RGD loop, we used surface plasmon resonance, electron cryo-microscopy, and image reconstruction to characterize the capsid-integrin interactions and the conformational changes on genome release. We show that the integrin binds to the capsid with nanomolar affinity and that the binding of integrin to the virion does not induce uncoating, thereby implying that further steps are required for release of the genome. Electron cryo-tomography and single-particle image reconstruction revealed variation in the number and conformation of the integrins bound to the capsid, with the integrin footprint mapping close to the predicted site for the exposed RGD loop on VP1. Comparison of empty and RNA-filled capsid reconstructions showed that the capsid undergoes conformational changes when the genome is released, so that the RNA-capsid interactions in the N termini of VP1 and VP4 are lost, VP4 is removed, and the capsid becomes more porous, as has been reported for poliovirus 1, human rhinovirus 2, enterovirus 71, and coxsackievirus A7. These results are important for understanding the structural basis of integrin binding to CVA9 and the molecular events leading to CVA9 cell entry and uncoating.
Structural and functional analysis of coxsackievirus A9 integrin alphavbeta6 binding and uncoating.,Shakeel S, Seitsonen JJ, Kajander T, Laurinmaki P, Hyypia T, Susi P, Butcher SJ J Virol. 2013 Apr;87(7):3943-51. doi: 10.1128/JVI.02989-12. Epub 2013 Jan 30. PMID:23365426[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Shakeel S, Seitsonen JJ, Kajander T, Laurinmaki P, Hyypia T, Susi P, Butcher SJ. Structural and functional analysis of coxsackievirus A9 integrin alphavbeta6 binding and uncoating. J Virol. 2013 Apr;87(7):3943-51. doi: 10.1128/JVI.02989-12. Epub 2013 Jan 30. PMID:23365426 doi:10.1128/JVI.02989-12
