title: The crystallographic structure of Panicum Mosaic Virus (PMV).
abstract: The structure of Panicum Mosaic Virus (PMV) was determined by X-ray diffraction analysis to 2.9Å resolution. The crystals were of pseudo symmetry F23; the true crystallographic unit cell was of space group P2(1) with a=411.7Å, b=403.9Å and c=412.5Å, with β=89.7°. The asymmetric unit was two entire T=3 virus particles, or 360 protein subunits. The structure was solved by conventional molecular replacement from two distant homologues, Cocksfoot Mottle Virus (CfMV) and Tobacco Necrosis Virus (TNV), of ∼20% sequence identity followed by phase extension. The model was initially refined with exact icosahedral constraints and then with icosahedral restraints. The virus has Ca(++) ions octahedrally coordinated by six aspartic acid residues on quasi threefold axes, which is completely different than for either CfMV or TNV. Amino terminal residues 1-53, 1-49 and 1-21 of the A, B and C subunits, respectively, and the four C-terminal residues (239-242) are not visible in electron density maps. The additional ordered residues of the C chain form a prominent "arm" that intertwines with symmetry equivalent "arms" at icosahedral threefold axes, as was seen in both CfMV and TNV. A 17 nucleotide hairpin segment of genomic RNA is icosahedrally ordered and bound at 60 equivalent sites at quasi twofold A-B subunit interfaces at the interior surface of the capsid. This segment of RNA may serve as a conformational switch for coat protein subunits, as has been proposed for similar RNA segments in other viruses.
authors.affiliation: Department of Molecular Biology and Biochemistry, The University of California, Irvine, CA 92697-3900, USA.
authors.forename: Debora L
authors.initials: DL
authors.lastname: Makino
authors.forename: Steven B
authors.initials: SB
authors.lastname: Larson
authors.forename: Alexander
authors.initials: A
authors.lastname: McPherson
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002118:Calcium / Q000737:chemistry; D036022:Capsid Proteins / Q000737:chemistry*; D017124:Conserved Sequence; D056831:Coordination Complexes / Q000737:chemistry; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009029:Mosaic Viruses / Q000737:chemistry / Q000648:ultrastructure*; D008897:Panicum / Q000821:virology; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012367:RNA, Viral / Q000737:chemistry; D040681:Structural Homology, Protein; D013499:Surface Properties; D014771:Virion / Q000737:chemistry / Q000648:ultrastructure*
chemical_list: D036022:Capsid Proteins; D056831:Coordination Complexes; D012367:RNA, Viral; D002118:Calcium