title: Structural framework for DNA translocation via the viral portal protein.
abstract: Tailed bacteriophages and herpesviruses load their capsids with DNA through a tunnel formed by the portal protein assembly. Here we describe the X-ray structure of the bacteriophage SPP1 portal protein in its isolated 13-subunit form and the pseudoatomic structure of a 12-subunit assembly. The first defines the DNA-interacting segments (tunnel loops) that pack tightly against each other forming the most constricted part of the tunnel; the second shows that the functional dodecameric state must induce variability in the loop positions. Structural observations together with geometrical constraints dictate that in the portal-DNA complex, the loops form an undulating belt that fits and tightly embraces the helical DNA, suggesting that DNA translocation is accompanied by a 'mexican wave' of positional and conformational changes propagating sequentially along this belt.
authors.affiliation: York Structural Biology Laboratory, Department of Chemistry, University of York, York, UK.
authors.forename: Andrey A
authors.initials: AA
authors.lastname: Lebedev
authors.forename: Margret H
authors.initials: MH
authors.lastname: Krause
authors.forename: Anabela L
authors.initials: AL
authors.lastname: Isidro
authors.forename: Alexei A
authors.initials: AA
authors.lastname: Vagin
authors.forename: Elena V
authors.initials: EV
authors.lastname: Orlova
authors.forename: Joanne
authors.initials: J
authors.lastname: Turner
authors.forename: Eleanor J
authors.initials: EJ
authors.lastname: Dodson
authors.forename: Paulo
authors.initials: P
authors.lastname: Tavares
authors.forename: Alfred A
authors.initials: AA
authors.lastname: Antson
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D018360:Crystallography, X-Ray; D004279:DNA, Viral / Q000737:chemistry / Q000378:metabolism*; D019143:Evolution, Molecular; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D012399:Rotation; D055672:Static Electricity; D014764:Viral Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D019065:Virus Assembly
chemical_list: D004279:DNA, Viral; D021122:Protein Subunits; D014764:Viral Proteins; C115880:portal protein, Bacteriophage SPP1