Molecular Rearrangements Involved in the Capsid Shell Maturation of Bacteriophage T7

José R. Castón,José L. Carrascosa,Ana Cuervo,Jaime Martín-Benito,Javier A. Velázquez-Muriel,Alina Ionel,Daniel Luque,José M. Valpuesta

doi:10.1074/jbc.m110.187211

Abstract

Maturation of dsDNA bacteriophages involves assembling the virus prohead from a limited set of structural components followed by rearrangements required for the stability that is necessary for infecting a host under challenging environmental conditions. Here, we determine the mature capsid structure of T7 at 1 nm resolution by cryo-electron microscopy and compare it with the prohead to reveal the molecular basis of T7 shell maturation. The mature capsid presents an expanded and thinner shell, with a drastic rearrangement of the major protein monomers that increases in their interacting surfaces, in turn resulting in a new bonding lattice. The rearrangements include tilting, in-plane rotation, and radial expansion of the subunits, as well as a relative bending of the A- and P-domains of each subunit. The unique features of this shell transformation, which does not employ the accessory proteins, inserted domains, or molecular interactions observed in other phages, suggest a simple capsid assembling strategy that may have appeared early in the evolution of these viruses.

Highlights

Case of bacteriophages, which share a surprising degree of similarity, as well as common general mechanisms of the maturation leading to the infective virion [3,4,5]
Double-stranded DNA bacteriophages [9] have been instrumental to study basic principles in assembly and maturation of viral particles [10, 11]. dsDNA bacteriophages first assemble into an icosahedral prohead composed of a defined number of monomers of the main shell protein, scaffolding proteins, and a dodecameric connector
The fold of the shell protein was first described for the bacteriophage HK97 [12, 13] and later found in other viruses such as P22 [14], T4 [4], ␾29 [15], HSV-1 [7], ⑀15 [16], T7 [17], and lambda [18]

Summary

Introduction

Case of bacteriophages, which share a surprising degree of similarity, as well as common general mechanisms of the maturation leading to the infective virion [3,4,5]. Different bacteriophages incorporate additional domains in the main shell protein fold, resulting in different assembly mechanisms.

Results

Conclusion