2bbv
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(New page: 200px<br /><applet load="2bbv" size="450" color="white" frame="true" align="right" spinBox="true" caption="2bbv, resolution 2.800Å" /> '''THE REFINED THREE-D...)
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Revision as of 06:35, 21 November 2007
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THE REFINED THREE-DIMENSIONAL STRUCTURE OF AN INSECT VIRUS AT 2.8 ANGSTROMS RESOLUTION
Overview
The structure of the black beetle nodavirus has been refined at 2.8 A, resolution by alternate use of restrained least-squares atomic coordinate, refinement and phase refinement by real space averaging with the 5-fold, non-crystallographic symmetry in the crystal. The coordinates were also, refined by simulated annealing. The final R-factor for all data with, I/sigma(I) > 4 was 22.1%. A total of 7692 atoms were refined in one, icosahedral asymmetric unit which included 273 oxygen atoms of ordered, water molecules. Three identical gene products of 407 amino acids form one, icosahedral asymmetric unit. Each is located in a structurally unique, position, identified as A, B or C, consistent with a T = 3 quasi, equivalent lattice. Icosahedral pentamers are formed by A subunits while B, and C subunits alternate about icosahedral 3-fold axes to form quasi, hexamers. Five calcium ions are located within the icosahedral asymmetric, unit and stabilize the quasi 3-fold related intersubunit contacts between, A, B and C. The final model consists of coordinates for residues 56 to 379, of all three subunits and residues 20 to 31 from the C subunit only. Atom, positions for the sugar-phosphate backbone were modeled for ten, nucleotides close to the icosahedral 2-fold axes. Symmetry equivalent, polyribonucleotides form a helical duplex at each icosahedral 2-fold axis., The three subunits display an eight-stranded beta-barrel fold, very, similar to the subunit structures observed in most other icosahedral RNA, viruses analyzed. Quasi equivalence is regulated by the ordered RNA and, residues 20 to 31 in the C subunit to form a "flat inter subunit contact", at icosahedral 2-fold joints. The RNA and polypeptide are disordered at, the quasi 2-fold joints and this results in a "bent inter subunit, contact". Although similar quaternary structures were seen in T = 3 plant, viruses studied, RNA did not play a role as a molecular switch in those, structures. The autocatalytic, post assembly, cleavage of the initial gene, product at residue Asn363/Ala364 to form a stable and infectious particle, is probably the result of an acid catalyzed main-chain hydrolysis in which, Asp75 is the proton donor. The reaction is initiated by assembly which, places Asp75 in a hydrophobic environment created by quaternary, interactions which raises its pK to 5.6. The region in which the reaction, occurs is formed by an internal helical bundle that has not been seen in, other virus structures.
About this Structure
2BBV is a Protein complex structure of sequences from Black beetle virus with CA as ligand. Full crystallographic information is available from OCA.
Reference
The refined three-dimensional structure of an insect virus at 2.8 A resolution., Wery JP, Reddy VS, Hosur MV, Johnson JE, J Mol Biol. 1994 Jan 14;235(2):565-86. PMID:8289282
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