Structure and host-cell interaction of SH1, a membrane-containing, halophilic euryarchaeal virus.

The Archaea, and the viruses that infect them, are the least well understood of all of the three domains of life. They often grow in extreme conditions such as hypersaline lakes and sulfuric hot springs. Only rare glimpses have been gained into the structures of archaeal viruses. Here, we report the subnanometer resolution structure of a recently isolated, hypersalinic, membrane-containing, euryarchaeal virus, SH1, in which different viral proteins can be localized. The results indicate that SH1 has a complex capsid formed from single beta-barrels, an important missing link in hypotheses on viral capsid protein evolution. Unusual, symmetry-mismatched spikes seem to play a role in host adsorption. They are connected to highly organized membrane proteins providing a platform for capsid assembly and potential machinery for host infection.