# Aviadenovirus structure: A highly thermostable capsid in the absence of stabilizing proteins

## TL;DR

This paper reveals the unique structure of a poultry adenovirus that remains stable without certain stabilizing proteins, offering insights into virus evolution and potential applications in vector development.

## Contribution

The study presents the first high-resolution structure of an aviadenovirus and identifies unique structural features contributing to its thermostability.

## Key findings

- FAdV-C4 lacks stabilizing proteins but remains highly thermostable.
- The hexon protein has a large insertion and a long N-terminal tail.
- Protein IIIa resembles atadenoviruses, while protein VIII is structurally unique.

## Abstract

High-resolution structural studies have mainly focused on two out of the six adenovirus genera: mastadenoviruses and atadenoviruses. Here we report the high-resolution structure of an aviadenovirus, the poultry pathogen fowl adenovirus serotype 4 (FAdV-C4). FAdV-C4 virions are highly thermostable, despite lacking minor coat and core proteins shown to stabilize the mast- and atadenovirus particles, having no genus-specific cementing proteins, and packaging a 25% longer genome. Unique structural features of the FAdV-C4 hexon include a large insertion at the trimer equatorial region, and a long N-terminal tail. Protein IIIa conformation is closer to atadenoviruses than to mastadenoviruses, while protein VIII diverges from all previously reported structures. We interpret these differences in light of adenovirus evolution. Finally, we discuss the possible role of core composition in determining capsid stability properties. These results enlarge our view on the structural diversity of adenoviruses, and provide useful information to counteract fowl pathogens or use non-human adenoviruses as vectors.

The International Committee for Virus Taxonomy currently recognizes over 120 adenovirus species, grouped in six genera, with host range covering all kinds of vertebrates. Although all adenoviruses share a common core of genes involved in genome replication and capsid assembly, knowledge on the structural variability within the family, as well as its relation with evolution and tropism, is still scarce. Understanding the physical and architectural properties of different adenoviruses is critical to understand their infectious cycle, fight against adenovirus-caused infections, and tailor new adenovirus-based vectors. Here we provide the first high-resolution structure of an aviadenovirus, a pathogen of economical relevance in the poultry industry and an interesting candidate for the development of heat-stable, non-human adenovirus vectors.