Portal protein functions akin to a DNA-sensor that couples genome-packaging to icosahedral capsid maturation

Ravi K. Lokareddy, Rajeshwer S. Sankhala, Ankoor Roy, Pavel V. Afonine, Tina Motwani, Carolyn M. Teschke, Kristin N. Parent and Gino Cingolani ()
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Ravi K. Lokareddy: Thomas Jefferson University
Rajeshwer S. Sankhala: Thomas Jefferson University
Ankoor Roy: Thomas Jefferson University
Pavel V. Afonine: Lawrence Berkeley National Laboratory
Tina Motwani: University of Connecticut
Carolyn M. Teschke: University of Connecticut
Kristin N. Parent: Michigan State University
Gino Cingolani: Thomas Jefferson University

Nature Communications, 2017, vol. 8, issue 1, 1-11

Abstract: Abstract Tailed bacteriophages and herpesviruses assemble infectious particles via an empty precursor capsid (or ‘procapsid’) built by multiple copies of coat and scaffolding protein and by one dodecameric portal protein. Genome packaging triggers rearrangement of the coat protein and release of scaffolding protein, resulting in dramatic procapsid lattice expansion. Here, we provide structural evidence that the portal protein of the bacteriophage P22 exists in two distinct dodecameric conformations: an asymmetric assembly in the procapsid (PC-portal) that is competent for high affinity binding to the large terminase packaging protein, and a symmetric ring in the mature virion (MV-portal) that has negligible affinity for the packaging motor. Modelling studies indicate the structure of PC-portal is incompatible with DNA coaxially spooled around the portal vertex, suggesting that newly packaged DNA triggers the switch from PC- to MV-conformation. Thus, we propose the signal for termination of ‘Headful Packaging’ is a DNA-dependent symmetrization of portal protein.

Date: 2017
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DOI: 10.1038/ncomms14310

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