High resolution X-ray diffraction data from 5 micron diameter protein crystals - towards the atomic structure of insect virus polyhedra

School of Biological Sciences, University of Auckland* Kyoto Institute of Technology** Alta Pharma AG, Germany*** Swiss Light Source, Switzerland****
â—‹Peter Metcalf* Fasseli Coulibaly* Elaine Y Chiu* Hajime Mori** Peter Haebel*** Sascha Guttman**** Clemens Schulze-Briese****

Polyhedra are remarkably stable protein microcrystals that form within the cells of insects infected with either of the two viruses Cytoplasmic Polyhedrosis Virus (CPV) or Nucleopolyhedrosis Virus (NPV or baculovirus). Polyhedra are cubic crystals consisting of the virus encoded ~28kD protein polyhedrin. Polyhedra in infected cells also occlude virus particles as the crystals grow and these crystals then become the natural infective form of these viruses after the death and decay of the infected insect. When ingested by insects, polyhedra dissolve in the midgut releasing the occluded virus particles to start a new cycle of infection. We have developed techniques to collect single crystal X-ray diffraction data from 5-7 micron diameter polyhedra using the Swiss Light Source PX1 micro-beam line. The crystals diffract to at most 1.7 Angstrom resolution but decay rapidly in the beam. NPV and CPV crystals have similar unit cell dimensions and symmetry, despite the lack of sequence homology and the different phylogenetic origin of these viruses (CPV is a dsRNA virus and NPV is a dsDNA virus). I will describe our efforts to determine the atomic structure of these micro-crystals.