Cryo-EM structures show how vertical single β-barrel viruses manage self-assembly

In 1977, Carl Woese et al introduced the three-domain system of biological classification that divides life forms into Archaea, Bacteria and Eukaryotes. This was the first time that the differences between Archaea and Bacteria were recognized. The first observed archaea were extremophiles, able to survive and thrive in extremely harsh conditions, but ongoing research has found them in a wide range of habitats; they are particularly abundant in the oceans. Archaea form part of the microbiota of all organisms, including humans, and their unique survival capabilities mean they can be used to enhance our understanding of early life on Earth. We are just beginning to investigate viruses that can infect Archaea, and in work recently published in Nature Communications, an international team of researchers determined the near-atomic structures of HCIV-1 and HHIV-2 by cryo-electron microscopy (cryo-EM). Their results show how nature has solved the complexity of arranging vertical single β-barrels and provide insights into the evolutionary consequences of the fusion event of the two consecutive major capsid protein (MCP) genes, which has ultimately led to the membrane-less vertical double β-barrel MCP assembly seen in adenovirus.