The structure of the Human Adenovirus 7 virus-like particles reveals that pentons and core-genome promote hexon-pIIIa interactions during capsid maturation

Abstract

Members of the Adenoviridae family routinely infect humans, exhibit significant genetic diversity, and are associated with a variety of illnesses. Types 4 and 7 frequently circulate in the United States and are major causes of respiratory disease. Infections can result in hospitalization and, in severe cases, death. Although a live wild-type-virus vaccine targeting these two types exists, its use is restricted to military personnel due to concerns about viral-shedding and the potential for genetic recombination. To overcome these limitations, we recently developed a virus-like particle (VLP) platform as an alternative vaccination strategy. These VLPs are stable, lack genomic material, and elicit a potent humoral immune response in mice, effectively neutralizing adenoviral infection. Here, we describe the cryo-EM structure of these VLPs at near atomic resolution. Structural insights are essential to ensure that the neutralizing antigens displayed on the VLPs accurately mimic those of the infectious virion, guide the design of particles with improved stability and efficacy, and enable engineering of VLPs with antigenic properties targeting multiple adenovirus types. The structure confirms that the key epitopes capable of eliciting neutralizing antibodies are appropriately displayed for antibody recognition. It also reveals previously unobserved interactions critical for capsid maturation. The penton base adopts multiple conformations when interacting with hexons, and its proper positioning is necessary to facilitate hexon-pIIIa interactions that stabilize the capsid. A comparison of the VLP with immature and mature adenovirus structures shows that core-genome packaging strengthens interaction between cementing proteins pIIIa and pVIII and the hexon shell. Significance StatementAdenoviruses are large and morphologically complex family of viruses that undergo a sophisticated process of assembly and maturation. These viruses are responsible for ocular, respiratory, and enteric infections, posing a particular risk to children and the immunocompromised. Despite their clinical significance, there are no adenovirus vaccines available to the public. Here we report the cryo-electron microscopy structure of human adenovirus 7 virus-like particles, which have shown strong potential as a vaccine candidate. Our analysis provides critical insights for the design of particles as vaccines or carriers of genetic therapeutics. The structure reveals how interaction between hexon and penton promote cement protein pIIIa for increased capsid interaction, and how core-genome packaging contributes to capsid maturation and enhanced capsid stability.