Exit and assembly of hyperthermophilic archaeal viruses – EXAVIR

Viruses of the Archaea constitute an integral but unique part of the virosphere. A significant portion of archaeal viruses displays morphotypes — bottle-shaped, lemon-shaped, droplet-shaped, etc. — not known to be associated with the other two cellular domains, Bacteria and Eukarya. Even after a few decades of exploration, novel virion morphologies are constantly being discovered. Furthermore, distinctiveness of archaeal viruses extends to their genome sequences and the structure of proteins they encode. The ways these viruses interact with their hosts are therefore also likely to be unique, as revealed by the recent discovery of a novel virus egress mechanism that involves the formation of specific pyramidal structures on the host cell surface. However, until now, the studies on archaeal viruses were mostly confined to biochemical and genetic characterization of their virions and the knowledge on virus-host interplay in Archaea is minuscule compared to the wealth of data available on bacterial and eukaryotic systems. The major objective of the proposed project is to fill this gap and to obtain a more comprehensive understanding of molecular mechanisms at play in the archaeal virosphere.

For understanding archaeal virus–host interactions, we propose to focus on two fundamental stages of the life cycles of hyperthermophilic crenarchaeal viruses: the assembly of virions and their release from the host cell. For the studies, we selected three distinct virus-host model systems, which collectively should provide insights into the diversity of basic strategies employed by archaeal viruses in extreme geotermal habitats. The egress and assembly of non-enveloped viruses will be studied on the examples of Sulfolobus islandicus rod-shaped virus 2 (SIRV2) and Aeropyrum pernix bacilliform virus 1 (APBV1), while the mechanisms employed by enveloped viruses will be investigated using Sulfolobus spindle-shaped virus 1 (SSV1) as a model.

The studies proposed in the current research program are novel and have not been previously performed for other archaeal virus-host systems. The generated information will substantially contribute to global understanding on molecular mechanisms of virus-host interactions in Archaea. Reaching the research objectives is expected to reveal not only fundamental principles of virus biology, but those of the host organisms as well. The obtained information will allow the comparison of the solutions for the orchestrated virion assembly and release utilized by viruses infecting hosts from all three domains of life. Such comparisons would provide unique possibilities for decoding the history of emergence and development of viral strategies governing interactions with their host cells. Moreover, they may help to reveal the unsuspected evolutionary connections in the virosphere.

Knowledge on remodelling of biological membranes (SSV1 studies) and opening of virus-encoded gateway structures (SIRV2 studies) might prove to be important not only from the purely scientific point of view, but also for biotechnological purposes. Similarly, the studies on the self assembly of the APBV1 virions may have technological implications, by offering a possibility of targeted modification of virion properties by its assembly from amended protein constituents, and thus open a prospect of developing new nanotechnological materials.