Fibers come and go: differences in cell-entry components among related dsRNA viruses

Encapsidated dsRNA viruses, most of which are nonenveloped, infect a wide variety of hosts, from bacteria to vertebrates, and are currently grouped into 9 families comprising 33 genera. Given this range, it is not surprising that substantial diversity is seen in their transmission strategies and cell-entry machineries. One interesting set of recent findings is that several of these viruses, otherwise closely related, exhibit major differences in their entry machineries without comparably major differences in their capsid organizations. Examples are presence or absence of receptor-binding fibers among orthoreoviruses and aquareoviruses and presence or absence of both binding and membrane-penetration modules among totiviruses and between picobirnaviruses and partitiviruses. Evolved differences in cell-entry components among these viruses are therefore not only common but also seemingly straightforward from a structural standpoint.