CRYSTAL STRUCTURE OF AN INSECT PICORNA-LIKE VIRUS

Lars Liljas^1,2, John Tate¹, Tianwei Lin¹, Paul Scotti³, Peter Christian⁴ and John E. Johnson¹

¹The Scripps Research Institute, La Jolla, CA, USA,
²Uppsala University, Uppsala, Sweden,
³The Horticulture and Food Research Institute of New Zealand Ltd, Auckland, New Zealand,
⁴CSIRO Division of Entomology, Canberra, Australia

Cricket paralysis virus is an insect RNA virus which has been classified as a picornavirus, but recently it has been shown to have a different genetic organization than animal picornaviruses. The crystal structure of the virus has been determined at 3.0 A resolution. Data collected from a single frozen crystal showed that the crystal packing changed from one state to another during data collection. The structure was solved using molecular replacement at 6 A using the crystal structure of poliovirus, followed by phase extension to 3 A resolution. The structure shows similarities to picornaviruses but have several unique features. The conformation and arrangement of the VP1, VP2 and VP3 subunits are similar to picornaviruses, but a protein corresponding to VP4 seems to be the result of cleavage of the N-terminus of VP3 rather than of VP2. The conformation of this protein is different from what is found in picornaviruses, and symmetry-related VP4 molecules are interacting around the five-fold axes. The N-terminus of VP2 has a similar fold as in picornaviruses, but compared to these viruses, the N-termini of two VP2 molecules are exchanged at the two-fold axes. These N-termini create an extensive network of subunit-subunit interaction at the inner surface of the shell. There is no distinct canyon in this virus, and there is no pocket in VP1 which can accomodate molecules known to stabilize the capsids in the case of many picornaviruses.