Crystallization was performed using the sitting-drop vapor diffusion method. The crystals of PcTS1 were grown under 0.2 M Potassium formate and 20% polyethylene glycol (PEG) 3350 at 4 °C; crystals of PcTS1-Mg 2+ were grown under 0.2 M Tri-lithium citrate and 20% PEG 3350 at 4 °C. These crystals were harvested for data collection at 100 K. All data were collected at SSRF BL19U and BL10U2, processed with HKL2000 . For phase determination of PcTS1, molecular replacement was adopted using the structure of TS from Eleutherobia rubra CWA1 (PDB ID: 7S5L, 40% identity) as a starting model. The molecular replacement solution was outstanding, and an automatic model building was performed with PHENIX . Additional model building was done manually with Coot .