title: The structural basis of recognition and removal of cellular mRNA 7-methyl G 'caps' by a viral capsid protein: a unique viral response to host defense.
abstract: The single segment, double-stranded RNA genome of the L-A virus (L-A) of yeast encodes two proteins: the major coat protein Gag (76 kDa) and the Gag-Pol fusion protein (180 kDa). The icosahedral L-A capsid is formed by 120 copies of Gag and has architecture similar to that seen in the reovirus, blue tongue virus and rice dwarf virus inner protein shells. Gag chemically removes the m7GMP caps from host cellular mRNAs. Previously we identified a trench on the outer surface of Gag that included His154, to which caps are covalently attached. Here we report the refined L-A coordinates at 3.4 angstroms resolution with additional structural features and the structure of L-A with bound m7GDP at 6.5 angstroms resolution, which shows the conformational change of the virus upon ligand binding. Based on site-directed mutations, residues in or adjacent to the trench that are essential (or dispensable) for the decapping reaction are described here. Along with His154, the reaction requires a cluster of positive charge adjoining the trench and residues Tyr 452, Tyr150 and either Tyr or Phe at position 538. A tentative mechanism for decapping is proposed.
authors.affiliation: Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Jinghua
authors.initials: J
authors.lastname: Tang
authors.forename: Hisashi
authors.initials: H
authors.lastname: Naitow
authors.forename: Nora A
authors.initials: NA
authors.lastname: Gardner
authors.forename: Anna
authors.initials: A
authors.lastname: Kolesar
authors.forename: Liang
authors.initials: L
authors.lastname: Tang
authors.forename: Reed B
authors.initials: RB
authors.lastname: Wickner
authors.forename: John E
authors.initials: JE
authors.lastname: Johnson
mesh_terms: D001665:Binding Sites; D002213:Capsid / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D015226:Dinucleoside Phosphates / Q000378:metabolism*; D015683:Gene Products, gag / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry / Q000235:genetics; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D010649:Phenylalanine / Q000737:chemistry / Q000235:genetics; D012315:RNA Caps / Q000302:isolation & purification / Q000378:metabolism*; D012328:RNA Viruses / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012330:RNA, Double-Stranded / Q000302:isolation & purification / Q000378:metabolism*; D014443:Tyrosine / Q000737:chemistry / Q000235:genetics; D014779:Virus Replication
chemical_list: D015226:Dinucleoside Phosphates; D015683:Gene Products, gag; D012315:RNA Caps; D012330:RNA, Double-Stranded; D014443:Tyrosine; D010649:Phenylalanine; D006639:Histidine; C062229:7-methyl-diguanosine triphosphate