Poxviruses package viral redox proteins in lateral bodies and modulate the host oxidative response

Author summaryVaccinia virus is the prototype member of the Poxviridae family, whose members include monkeypox and variola virus, the causative agent of smallpox. All poxvirus particles, including vaccinia, are large and complex containing upwards of 70 different viral proteins.Virions are composed of 3 main viral sub-structures: cores which house the viral genome, two proteinaceous lateral bodies thought to deliver host modulatory proteins, and the viral membrane that harbors proteins required for virus structure, binding and entry. While the protein composition of VACV cores and membranes is well known, for technical reasons the collection of viral and cell proteins that reside in lateral bodies remains undefined. Here, we used a combination of controlled particle degradation and quantitative comparative mass spectrometry to identify viral and cellular candidate lateral body proteins. This revealed a large compendium of candidate lateral body cell and viral proteins for future analysis and uncovered viral redox proteins as a potential new class of poxvirus immunomodulators that are delivered to host cells via lateral bodies. All poxviruses contain a set of proteinaceous structures termed lateral bodies (LB) that deliver viral effector proteins into the host cytosol during virus entry. To date, the spatial proteotype of LBs remains unknown. Using the prototypic poxvirus, vaccinia virus (VACV), we employed a quantitative comparative mass spectrometry strategy to determine the poxvirus LB proteome. We identified a large population of candidate cellular proteins, the majority being mitochondrial, and 15 candidate viral LB proteins. Strikingly, one-third of these are VACV redox proteins whose LB residency could be confirmed using super-resolution microscopy. We show that VACV infection exerts an anti-oxidative effect on host cells and that artificial induction of oxidative stress impacts early and late gene expression as well as virion production. Using targeted repression and/or deletion viruses we found that deletion of individual LB-redox proteins was insufficient for host redox modulation suggesting there may be functional redundancy. In addition to defining the spatial proteotype of VACV LBs, these findings implicate poxvirus redox proteins as potential modulators of host oxidative anti-viral responses and provide a solid starting point for future investigations into the role of LB resident proteins in host immunomodulation.

Automated summary

This study investigates the composition of poxviruses and the role of poxvirus redox proteins in host cells. Using mass spectrometry, a large number of candidate cellular and viral proteins, including redox proteins, were identified. The results show that poxvirus infection has an antioxidative effect on host cells and deletion of redox proteins is insufficient to modulate host cell redox reactions, suggesting the existence of functional redundancy.