Capsid opening enables genome release of iflaviruses.

Karel Škubník,Robert Vácha,Lukáš Sukeník,Lenka Šmerdová,Jana Moravcová,Michaela Procházková,Antonín Přidal,Tibor Füzik,David Buchta,Pavel Plevka

doi:10.1126/sciadv.abd7130

Abstract

The family Iflaviridae includes economically important viruses of the western honeybee such as deformed wing virus, slow bee paralysis virus, and sacbrood virus. Iflaviruses have nonenveloped virions and capsids organized with icosahedral symmetry. The genome release of iflaviruses can be induced in vitro by exposure to acidic pH, implying that they enter cells by endocytosis. Genome release intermediates of iflaviruses have not been structurally characterized. Here, we show that conformational changes and expansion of iflavirus RNA genomes, which are induced by acidic pH, trigger the opening of iflavirus particles. Capsids of slow bee paralysis virus and sacbrood virus crack into pieces. In contrast, capsids of deformed wing virus are more flexible and open like flowers to release their genomes. The large openings in iflavirus particles enable the fast exit of genomes from capsids, which decreases the probability of genome degradation by the RNases present in endosomes.

Highlights

The family Iflaviridae of insect viruses includes important pathogens of the western honeybee (Apis mellifera): deformed wing virus (DWV), sacbrood virus (SBV), and slow bee paralysis virus (SBPV) [1]
We show that acidic pH induces expansion of the RNA genome in the DWV particle, which, in turn, triggers the swelling and flower- like opening of its capsid
Capsids of SBV and SBPV crack into pieces to enable genome release

Summary

Introduction

The family Iflaviridae of insect viruses includes important pathogens of the western honeybee (Apis mellifera): deformed wing virus (DWV), sacbrood virus (SBV), and slow bee paralysis virus (SBPV) [1]. The capsids of SBV and SBPV do not expand at acidic pH and retain their native conformation before the genome release In silico simulations show that, at acidic pH, the capsid proteins of SBPV and SBV mediated attractive interactions between pentamers to distances shorter than 1 nm (Fig. 3A).

Results

Conclusion