Structure characterization

Crystallization screening was conducted by the sitting‐drop vapor diffusion method using commercially available crystallization screens from Hampton Research. The crystallization screens were set up at 289 K at a concentration of 22 mg/mL. Diffraction‐quality crystals for E_1r26_M1a were obtained from the condition of 0.2 M potassium tartrate, 0.1 M sodium citrate pH 5.6, and 2.0 M ammonium sulfate. Crystals appeared in 8 days. All crystals were shortly soaked in reservoir solution supplemented with 15% glycerol (vol/vol) and then flash frozen in liquid nitrogen. The diffraction data were collected on BL17U131 at 0.9791 Å, and processed by using the XDS program.32 The initial structure was solved by molecular replacement in PHENIX33 with structure of thioredoxin from Trypanosoma brucei (PDB: 1r26) as the search model.24 Then all the models were refined manually and built with Coot.34 The final structures were refined by PHENIX.