Potassium induces conformational changes in the Sabia virus spike complex

Hemorrhagic fever viruses from the Arenaviridae are a source of concern due to their potential to cause lethal outbreaks and the lack of effective therapeutics. Several Clade-B viruses, which are endemic to the Americas, are pathogens that sporadically infect humans following zoonotic transmission from small rodents. Brazilian hemorrhagic fever, caused by the Sabia virus (SBAV), is one of several such diseases from Clade-B arenaviruses. Despite their importance and the risks they impose, many fundamental questions remain regarding their biology and function. Here, we present the structure of the spike complex from the Sabia virus, which mediates viral attachment and entry to the host cells. Our study reveals two distinct conformational states of the spike, representing its native closed state and an open state that it assumes during cell entry. We show that potassium, in combination with acidic pH, promotes the opening of the spike, which is required for achieving efficient cell entry. This structure further informs us about the architecture of Clade-B arenaviral spikes and how they vary from spikes of other members of the Arenaviridae.