Dengue virus 3 NS5 methyltransferase domain: expression, purification, crystallization and first structural data from microcrystalline specimens

Flavivirus infections often provoke life-threatening diseases of epidemic magnitudes, thus extensive research is currently directed towards the development of efficient vaccines and approved antiviral compounds. We present here the expression, purification, crystallization and preliminary X-ray diffraction analysis of one of the components of the flavivirus replication complex, the nonstructural protein 5 (NS5) mRNA methyltransferase (MTase) domain, from an emerging pathogenic flavivirus, dengue virus 3 (DEN3). Polycrystalline precipitates of DEN3 NS5 MTase, suitable for X-ray powder diffraction (XRPD) measurements, were produced in the presence of PEG 8000 (25 32.5% (w/v)), 0.1 M Tris-Amino, in a pH range from 7.0 to 8.0. A polymorph of orthorhombic symmetry (space group: P2(1)2(1)2, a=61.9 angstrom, b= 189.6 angstrom, c= 52.4 angstrom) was identified via XRPD. These results are the first step towards the complete structural determination of this molecule via XRPD and a parallel demonstration of the applicability of the method.