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 P 6 3 22, with unit‐cell parameters a  =  b  = 239.1, c = 106.5 Å. The crystal contained four PH0187 molecules in the asymmetric unit.