Drosophila suzukii is an invasive insect pest causing severe economic damage to fruit crops. Chemical pesticides are inefficient in controlling the spread of D. suzukii, therefore other strategies need to be deployed. One promising alternative is the utilization of entomopathogenic viruses. Advantage of viruses as a biopesticide is that they are host specific and have limited impact on non-targeted organisms.
Here we present cryo-EM structures of two such candidate biopesticides, La Jolla virus (LJV) and Motts Mill virus (MMV). Both, LJV and MMV, have small non-enveloped icosahedral capsids enclosing +ssRNA genomes. We have reconstructed virion and empty particle of LJV with respective resolutions 3.0 Å and 3.3 Å, and virion of MMV with resolution 2.7 Å.
LJV has been preliminary classified as an iflavirus and its overall virion structure follows the typical picornavirus-like pattern. The three capsid proteins VP1, VP2 and VP3 form a pseudo-T3 icosahedral shell with the diameter ~300 Å. Unlike the previously characterized iflaviruses of honeybees, LJV capsid does not contain surface domains or decoration proteins. The interpentamer contacts are stabilized by the N-termini of VP1 and VP2. These N-termini were not resolved in the empty particle resulting in the reduction of interpentamer contacts and expansion of the particle.
MMV is related to solemoviruses and tombusviruses. The capsid is arranged with icosahedral T3 quasi-symmetry with three copies of the coat protein forming the icosahedral asymmetric unit. The architecture of the virion is stabilized by the bivalent cation-mediated interactions of the coat proteins.