Expression, purification and crystallization of a novel nonstructural protein VP9 from white spot syndrome virus

The nonstructural protein VP9 from white spot syndrome virus (WSSV) has been identified and expressed in Escherichia coli. To facilitate purification, a cleavable His₆ tag was introduced at the N-terminus. The native protein was purified and crystallized by vapour diffusion against mother liquor containing 2 M sodium acetate, 100 mM MES pH 6.3, 25 mM cadmium sulfate and 3% glycerol. Crystals were obtained within 7 d and diffracted to 2.2 Å; they belonged to space group P2₁2₁2₁, with unit-cell parameters a = 74.13, b = 78.21, c = 78.98 Å and four molecules in the asymmetric unit. The selenomethionine-labelled protein produced isomorphous crystals that diffracted to approximately 3.3 Å.