Expression, purification, crystallization and preliminary X-ray analysis of the KaiC-like protein PH0187 from the hyperthermophilic archaeon Pyrococcus horikoshii OT3

KaiC is the central protein in the circadian rhythm in cyanobacteria. The 28 kDa KaiC-like protein PH0187 from the hyperthermophilic archaeon Pyrococcus horikoshii was expressed in Escherichia coli, purified and crystallized using the sitting-drop vapour-diffusion method at 293 K. Crystals of PH0187 were obtained using a reservoir solution consisting of 1.0 M ammonium phosphate monobasic and 0.1 M sodium citrate tribasic pH 5.3 (the final pH value of the reservoir solution was 4.8) and diffracted X-rays to 2.75 Å resolution. The crystal of PH0187 belonged to space group P6₃22, with unit-cell parameters a = b = 239.1, c = 106.5 Å. The crystal contained four PH0187 molecules in the asymmetric unit.