A thermostable xylose isomerase from Thermus caldophilus: biochemical characterization, crystallization and preliminary X-ray analysis

A highly thermostable xylose isomerase from Thermus caldophilus has been expressed in Escherichia coli. The purified enzyme has an optimum temperature of 363 K. It has been crystallized at room temperature using ammonium sulfate as a precipitant. The crystal belongs to the orthorhombic space group P2₁2₁2₁, with unit-cell parameters a = 84.35, b = 123.60, c = 140.24 Å. The presence of one molecule of tetrameric xylose isomerase in the asymmetric unit gives a crystal volume per protein mass (V_m) of 2.1 Å³ Da^-1 and a solvent content of 41% by volume. The crystals initially showed diffraction to 1.7 Å Bragg spacing with synchrotron X-­rays, and a set of native data extending to 2.3 Å resolution has been collected.