Structure and Function of P4, a dsRNA Virus Packaging Motor
Erika J. Mancini and Roman Tuma
from: Segmented Double-stranded RNA Viruses: Structure and Molecular Biology (Edited by: John T. Patton). Caister Academic Press, U.K. (2008)
This review focuses on the biochemical, biophysical, and structural characterization of P4, the protein that forms the packaging motor of the Cystoviridae family of dsRNA bacteriophages. P4 exists as a hexameric ring that is positioned atop the 5-fold vertices of the procapsid shell. The ATPase activity of P4 is coupled to translocation of the viral genomic precursors into the confines of a preformed procapsid. Recently determined structures of P4 from bacteriophage Φ12 in complex with nucleotide diphosphates and triphosphates together with the essential ion Mg2+ have captured snapshots of the packaging motor in different states along the catalytic pathway. Surprisingly, the structure of P4 shows a close similarity to RecA-like hexameric motors including the ubiquitous family of hexameric helicases. A model for the mechanism of action of P4 and other hexameric molecular motors has been proposed, which is the first model based on high-resolution structures captured along the catalytic pathway. The model was confirmed by biochemical data. While genomic packaging by P4 in the Cystoviridae family of dsRNA bacteriophages may share some features with dsDNA packaging by terminases of tailed bacteriophages, the implications of the present work for the mechanism of packaging in other dsRNA viruses are not obvious, but cannot be excluded read more ...