Crystallization and X-ray diffraction analysis of the RNA primer/promoter-binding domain of influenza A virus RNA-dependent RNA polymerase PB2

The C-terminal domain protein (amino-acid residues 535-759) of the PB2 subunit of the RNA-dependent RNA polymerase from the highly pathogenic influenza A virus was expressed as a soluble protein in Escherichia coli and crystallized using sodium formate as a precipitant. Data sets were collected from crystals of native and selenomethionine-substituted protein on the KEK NW12 beamline at the Photon Factory and the crystals diffracted to a maximum resolution of 2.44 Å for the SeMet-derivative crystal. The native crystals were found to belong to space group P3₂21, with unit-cell parameters a = b = 52.5, c = 156.3 Å. The Matthews value (V_M) was 2.7 Å³ Da^-1, assuming the presence of one molecule in the asymmetric unit. The SeMet-derivative crystals were found to belong to the same space group, with unit-cell parameters a = b = 52.6, c = 156.4 Å. Attempts are being made to solve the structure by multi-wavelength anomalous dispersion phasing.