Using cryo-electron tomography to elucidate the structural basis of the endosomal K+ requirement during Bunyavirus entry

The Bunyavirales order are the largest group of negative stranded RNA viruses, infecting humans as well as a bewildering array of animals and plants, in which select members cause severe or fatal disease. To enter host cells, bunyaviruses undergo endosomal transport to specific cellular destinations and exploit the changing environment of maturing endocytic vesicles to mediate genome release. Several virus-endosome fusion triggers have previously been identified, including endosomal potassium (K+) recently identified by our group. Specifically, we demonstrated a role for K+ channels and endosomal K+ concentration ([K+]) in the ‘priming’ of virions for fusion and uncoating events. Interestingly for Bunyamwera virus (BUNV), both a reduced pH and elevated [K+] were required to permit endosomal escape of the virus. To understand the molecular basis for this requirement we have used cryo-electron tomography to study the changes in virion structure upon K+ and pH treatment. These studies reveal why endosomal [K+] and K+ channels are required for bunyavirus entry, highlighting the potential of K+channels as druggable anti-viral targets.