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STRUCTURAL FACTORS THAT CONTROL CONFORMATIONAL TRANSITIONS AND SEROTYPE SPECIFICITY IN TYPE 3 POLIOVIRUS
[POLG_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.   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.   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.   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
The three-dimensional structure of the Sabin strain of type 3 poliovirus has been determined at 2.4 A resolution. Significant structural differences with the Mahoney strain of type 1 poliovirus are confined to loops and terminal extensions of the capsid proteins, occur in all of the major antigenic sites of the virion and typically involve insertions, deletions or the replacement of prolines. Several newly identified components of the structure participate in assembly-dependent interactions which are relevant to the biologically important processes of viral assembly and uncoating. These include two sites of lipid substitution, two putative nucleotides and a beta sheet formed by the N-termini of capsid proteins VP4 and VP1. The structure provides an explanation for the temperature sensitive phenotype of the P3/Sabin strain. Amino acids that regulate temperature sensitivity in type 3 poliovirus are located in the interfaces between promoters, in the binding site for a lipid substituent and in an assembly-dependent extended beta sheet that stabilizes the association of pentamers. Several lines of evidence indicate that these structural components also control conformational transitions at various stages of the viral life cycle.
Structural factors that control conformational transitions and serotype specificity in type 3 poliovirus.,Filman DJ, Syed R, Chow M, Macadam AJ, Minor PD, Hogle JM EMBO J. 1989 May;8(5):1567-79. PMID:2548847
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.