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Cryo-EM reconstruction of poliovirus-receptor complexCryo-EM reconstruction of poliovirus-receptor complex
Structural highlights
FunctionPOLG_POL1M 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. The interaction of five VP1 proteins in the fivefold axes results in a prominent protusion extending to about 25 Angstroms from the capsid shell. The resulting structure appears as a steep plateau encircled by a valley or cleft. This depression also termed canyon is the receptor binding site. The capsid interacts with human PVR at this site to provide virion attachment to target cell. This attachment induces virion internalization predominantly through clathrin- and caveolin-independent endocytosis in Hela cells and through caveolin-mediated endocytosis in brain microvascular endothelial cells. VP4 and VP1 subsequently undergo conformational changes leading to the formation of a pore in the endosomal membrane, thereby delivering the viral genome into the cytoplasm.[1] [2] [3] VP0 precursor is a component of immature procapsids (By similarity).[4] [5] [6] 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.[7] [8] [9] Protein 2B affects membrane integrity and cause an increase in membrane permeability (By similarity).[10] [11] [12] Protein 2C associates with and induces structural rearrangements of intracellular membranes. It displays RNA-binding, nucleotide binding and NTPase activities.[13] [14] [15] Protein 3A, via its hydrophobic domain, serves as membrane anchor. It also inhibits endoplasmic reticulum-to-Golgi transport (By similarity).[16] [17] [18] 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).[19] [20] [21] RNA-directed RNA polymerase 3D-POL replicates genomic and antigenomic RNA by recognizing replications specific signals (By similarity).[22] [23] [24] Publication Abstract from PubMedPoliovirus infection is initiated by attachment to a receptor on the cell surface called Pvr or CD155. At physiological temperature the receptor catalyzes an irreversible expansion of the virus to form an expanded form of the capsid called the 135S particle. This expansion results in the externalization of the myristoylated capsid protein VP4 and the N-terminal extension of the capsid protein VP1, both of which become inserted into the cell membrane. Structures of the expanded forms of poliovirus and of several related viruses have recently been reported. However, until now, it has been unclear how receptor binding triggers viral expansion at physiological temperature. Here, we report poliovirus in complex with an enzymatically partially deglycosylated form of the 3-domain ectodomain of Pvr at 4A resolution, as determined by electron cryomicroscopy. The interaction of the receptor with the virus in this structure is reminiscent of the interactions of Pvr with its natural ligands. At low temperature, the receptor induces very few changes in the structure of the virus, with the largest changes occurring within the footprint of the receptor, and in a loop of the internal protein VP4. Changes in the vicinity of the receptor include the displacement of a natural lipid ligand (called "pocket factor"), demonstrating that the loss of this ligand, alone, is not sufficient to induce particle expansion. Finally, analogies with naturally occurring ligand binding in the nectin family suggest which specific structural rearrangements in the virus-receptor complex could help to trigger the irreversible expansion of the capsid. IMPORTANCE: The cell-surface receptor (Pvr) catalyzes a large structural change in the virus that exposes membrane-binding protein chains. We fitted known atomic models of the virus and Pvr into three-dimensional experimental maps of the receptor-virus complex. The molecular interactions we see between poliovirus and its receptor are reminiscent of the nectin family, by involving the burying of otherwise-exposed hydrophobic groups. Importantly, poliovirus expansion is regulated by the binding of a lipid molecule within the viral capsid. We show that receptor binding either causes this molecule to be expelled or requires it, but that its loss is not sufficient to trigger irreversible expansion. Based on our model, we propose testable hypotheses to explain how the viral shell becomes destabilized, leading to RNA uncoating. These findings give us a better understanding of how poliovirus has evolved to exploit a natural process of its host to penetrate the membrane barrier. NECTIN-LIKE INTERACTIONS BETWEEN POLIOVIRUS AND ITS RECEPTOR TRIGGER CONFORMATIONAL CHANGES ASSOCIATED WITH CELL ENTRY.,Strauss M, Filman DJ, Belnap DM, Cheng N, Noel RT, Hogle JM J Virol. 2015 Jan 28. pii: JVI.03101-14. PMID:25631086[25] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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