Expression, purification, crystallization and preliminary crystallographic analysis of BipD, a component of theBurkholderia pseudomalleitype III secretion system

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Abstract
A construct consisting of residues 10-310 of BipD, a component of the Burkholderia pseudomallei type III secretion system (T3SS), has been overexpressed as a GST fusion, cleaved from the GST tag and purified. Crystals were grown of native and selenomethionine-labelled BipD. The crystals grow in two different polymorphs from the same condition. The first polymorph belongs to space group C222, with unit-cell parameters a = 103.98, b = 122.79, c = 49.17 Å, a calculated Matthews coefficient of 2.4 Å3 Da-1 (47% solvent content) and one molecule per asymmetric unit. The second polymorph belongs to space group P21212, with unit-cell parameters a = 136.47, b = 89.84, c = 50.15 Å, and a calculated Matthews coefficient of 2.3 Å3 Da-1 (45% solvent content) for two molecules per asymmetric unit (analysis of the self-rotation function indicates the presence of a weak twofold non-crystallographic symmetry axis in this P21212 form). The native crystals of both forms give diffraction data to 2.7 Å resolution, while the SeMet-labelled P21212 crystals diffract to 3.3 Å resolution. A K2PtCl4 derivative of the P21212 form was also obtained and data were collected to 2.7 Å with radiation of wavelength = 0.933 Å. The Pt-derivative anomalous difference Patterson map revealed two self-peaks on the Harker sections.

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