Our odyssey in the world of insect viruses

Professor Fasséli Coulibaly
Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology
Monash University, Clayton, Australia

Baculovirus is the prototype insect virus used in biotechnological applications ranging from bioinsecticides to vaccine and therapeutics production. Despite its beneficial contribution, surprisingly little was known about the molecular organisation and assembly of the baculovirus infectious particles until recently. Indeed, the atypical rod-shape morphology of the virion and absence of a recognisable major capsid from other double-stranded DNA viruses means that the evolutionary place of baculovirus has remained uncertain.

I will present a comprehensive structure-based characterisation of the prototype baculovirus AcMNPV using proteome-wide AlphaFold modelling, cryo-electron microscopy and cryo-electron tomography. Our structure of the nucleocapsid reveals a helical architecture with unique and unexpected features such as an extensive network of disulphide crosslinks and complex terminal structures capping the tubular nucleocapsid. Together with sensitive evolutionary analyses of all conserved non-structural proteins, these findings define the hallmarks of a new viral realm of double-stranded DNA viruses.

Exploring further unchartered regions of the virosphere, we have also characterised insect RNA viruses that form ovoid infectious particles with an atypical proteolipidic shell. We find that these viruses possess a fusion machinery that departs structurally and mechanistically from the main known classes of fusion proteins.

In this presentation, I will discuss how these findings change our view of evolutionary relationships between ancient virus taxa and potential mechanistic implications for virus-cell fusion.