Cryo-EM structure of Kashmir bee virus

Mukhamedova L., Fuzik T., Novacek J., Pridal A., Plevka P.

Masaryk University CEITEC - Central European Institute of Technology; Mendel University in Brno

 

Kashmir bee virus (KBV) infects many species of insect pollinators, including agriculturally indispensable honeybees Apis Mellifera and Apis Cerana. KBV replicates faster and can be more lethal than other viruses of honeybees, such as sacbrood bee virus, deformed wing virus and black queen cell virus. However, KBV can also persist in seemingly healthy insects for a long time as an unapparent infection. Like the other members of family Dicitroviridae, non-enveloped KBV virions contain positive sense single stranded RNA genome, coated with capsid, which is composed of three major capsid proteins VP1, VP2, VP3, and minor protein VP4. KBV is part of the acute bee paralysis – Kashmir bee – Israeli bee paralysis virus cluster of related viruses that are together worldwide distributed. Despite of the overall genome sequence identity of IAPV and KBV of 76% and amino acids sequence identity of the capsid proteins of 75%, the viruses cause different symptoms and have distinct structural properties. Here we report the structure of KBV virion determined to the resolution of 2.9 Å using cryo-electron microscopy. We show, that VP4 protein of KBV has two α-helixes at its C-terminus. These helices may increase the stability of the KBV capsid relative to the one of IAPV. We also show that VP3 protein forms a β-strand on its N-terminus. Five of these strands form a beta-annulus around fivefold axis of the virus capsid. This feature has not been observed before in any virus from the family Dicistroviridae.