Structural rearrangements between portal protein subunits are essential for viral DNA translocation.
Transport of DNA into preformed procapsids is a general strategy for genome packing inside virus particles. In most viruses, this task is accomplished by a complex of the viral packaging ATPase with the portal protein assembled at a specialized vertex of the procapsid. Such molecular motor translocates DNA through the central tunnel of the portal protein. A central question to understand this mechanism is whether the portal is a mere conduit for DNA or whether it participates actively on DNA translocation. The most constricted part of the bacteriophage SPP1 portal tunnel is formed by twelve loops, each contributed from one individual subunit. The position of each loop is stabilized by interactions with helix alpha-5, which extends into the portal putative ATPase docking interface. Here, we have engineered intersubunit disulfide bridges between alpha-5s of adjacent portal ring subunits. Such covalent constraint blocked DNA packaging, whereas reduction of the disulfide bridges restored normal packaging activity. DNA exit through the portal in SPP1 virions was unaffected. The data demonstrate that mobility between alpha-5 helices is essential for the mechanism of viral DNA translocation. We propose that the alpha-5 structural rearrangements serve to coordinate ATPase activity with the positions of portal tunnel loops relative to the DNA double helix.
Cuervo
Ana
A
Unité de Virologie Moléculaire et Structurale, Unité Mixte de Recherche (UMR) CNRS 2472, UMR Institut National de la Recherche Agronomique (INRA) 1157 and Institut Fédératif de Recherche 115, 91198 Gif-sur-Yvette Cedex, France.
Vaney
Marie-Christine
MC
Antson
Alfred A
AA
Tavares
Paulo
P
Oliveira
Leonor
L
D001435:Bacteriophages / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002213:Capsid / Q000737:chemistry / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000737:chemistry / Q000378:metabolism; D004279:DNA, Viral / Q000737:chemistry* / Q000378:metabolism*; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D003432:Cross-Linking Reagents; D004279:DNA, Viral; D004220:Disulfides; D021122:Protein Subunits; D014764:Viral Proteins; C115880:portal protein, Bacteriophage SPP1