The C-terminus of Sudan ebolavirus VP40 contains a functionally important CXnC motif, a target for redox modifications.

The Ebola virus matrix protein VP40 mediates viral budding and negatively regulates viral RNA synthesis. The mechanisms by which these two functions are exerted and regulated are unknown. Using a high-resolution crystal structure of Sudan ebolavirus (SUDV) VP40, we show here that two cysteines in the flexible C-terminal arm of VP40 form a stabilizing disulfide bridge. Notably, the two cysteines are targets of posttranslational redox modifications and interact directly with the host`s thioredoxin system. Mutation of the cysteines impaired the budding function of VP40 and relaxed its inhibitory role for viral RNA synthesis. In line with these results, the growth of recombinant Ebola viruses carrying cysteine mutations was impaired and the released viral particles were elongated. Our results revealed the exact positions of the cysteines in the C-terminal arm of SUDV VP40. The cysteines and/or their redox status are critically involved in the differential regulation of viral budding and viral RNA synthesis.

Immunogenicity and efficacy of the COVID-19 candidate vector vaccine MVA-SARS-2-S in preclinical vaccination.

Severe acute respiratory syndrome (SARS) coronavirus 2 (SARS-CoV-2) has emerged as the infectious agent causing the pandemic coronavirus disease 2019 (COVID-19) with dramatic consequences for global human health and economics. Previously, we reached clinical evaluation with our vector vaccine based on modified vaccinia virus Ankara (MVA) against the Middle East respiratory syndrome coronavirus (MERS-CoV), which causes an infection in humans similar to SARS and COVID-19. Here, we describe the construction and preclinical characterization of a recombinant MVA expressing full-length SARS-CoV-2 spike (S) protein (MVA-SARS-2-S). Genetic stability and growth characteristics of MVA-SARS-2-S, plus its robust expression of S protein as antigen, make it a suitable candidate vaccine for industrial-scale production. Vaccinated mice produced S-specific CD8+ T cells and serum antibodies binding to S protein that neutralized SARS-CoV-2. Prime-boost vaccination with MVA-SARS-2-S protected mice sensitized with a human ACE2-expressing adenovirus from SARS-CoV-2 infection. MVA-SARS-2-S is currently being investigated in a phase I clinical trial as aspirant for developing a safe and efficacious vaccine against COVID-19.