Crystallization and preliminary X-ray analysis of a putative sensor histidine kinase domain: the C-terminal domain of HksP4 from Aquifex aeolicus VF5.

The histidine kinase domain of the cytoplasmic protein HksP4 from the hyperthermophilic bacterium Aquifex aeolicus VF5, located in the C-terminal half of the protein, was expressed, purified and crystallized. Diffraction-quality crystals were obtained in the presence of adenosine triphosphate (ATP) or adenosine 5'-(β,γ-imido)triphosphate (AMPPNP) by the sitting-drop vapour-diffusion method using PEG 3350 as the precipitant. The crystals obtained in the presence of ATP and AMPPNP diffracted X-rays to 3.1 and 2.9 Å resolution, respectively, on BL-5A at Photon Factory (Ibaraki, Japan) and were found to belong to the same space group P2(1)2(1)2(1), with unit-cell parameters a=80.2, b=105.5, c=122.0 Å and a=81.5, b=105.5, c=130.9 Å, respectively. Their Matthews coefficients (VM=2.74 and 2.51 Å3 Da(-1), respectively) indicated that both crystals contained four protein molecules per asymmetric unit.