Expression, crystallization and preliminary X-ray diffraction analysis of the N-terminal domain of nsp2 from avian infectious bronchitis virus

Avian infectious bronchitis virus (IBV) is a prototype of the group III coronaviruses and encodes 15 nonstructural proteins which make up the transcription/replication machinery. The nsp2 protein from IBV has a unique and novel sequence and has no experimentally confirmed function in replication, whereas it has been proposed to be crucial for early viral infection and may inhibit the early host immune response. The gene that encodes a double-mutant IBV nsp2 N-terminal domain (residues 9–393 of the polyprotein, with mutations Q132L and L270F) was cloned and expressed in Escherichia coli and the protein was subjected to crystallization trials. The crystals diffracted to 2.5 Å resolution and belonged to space group P6₂ or P6₄, with unit-cell parameters a = b = 114.2, c = 61.0 Å, α = β = 90, γ = 120°. Each asymmetric unit contained one molecule.