Purification, crystallization and preliminary X-ray analysis of nonstructural protein 2 (nsp2) from avian infectious bronchitis virus

Avian infectious bronchitis virus (IBV) is a member of the group III coronaviruses, which differ from the other groups of coronaviruses in that they do not encode the essential pathogenic factor nonstructural protein 1 (nsp1) and instead start with nsp2. IBV nsp2 is one of the first replicase proteins to be translated and processed in the viral life cycle; however, it has an entirely unknown function. In order to better understand the structural details and functional mechanism of IBV nsp2, the recombinant protein was cloned, overexpressed in Escherichia coli, purified and crystallized. The crystals diffracted to 2.8 Å resolution and belonged to space group P2₁, with unit-cell parameters a = 57.0, b = 192.3, c = 105.7 Å, β = 90.8°. Two molecules were found in the asymmetric unit; the Matthews coefficient was 3.9 ų Da⁻¹, corresponding to a solvent content of 68.2%.