The ligand-free form crystals were grown at room temperature in sitting drops. A final concentration of 5 mM ADP, 1:100 chymotrypsin (w/w) were added into the protein stock solution and 0.5 mL protein solution was mixed immediately with 0.5 mL well solution containing 15% polyethylene glycol (PEG) 4000, 0.2 M ammonium acetate, 0.1 M sodium citrate, pH 5.6 and set up for vapour diffusion crystallization. The SeMet crystal used for structure determination was grown in 14.55% PEG4000, 0.2 M ammonium acetate, 0.1 M sodium citrate, pH 6.0, with 1:100 chymotrypsin (w/w) and 5 mM ADP in a sitting drop setup. Crystals grew to a mountable size within 24 hours. Paratone oil was used to cryo-protect the crystals.