2.2 Structure modelling and molecular docking
The homology model of Mc SuSy was constructed using the YASARA program.[30] The structures of UDP and sucrose were obtained from ZINC database (http://zinc.docking.org/).To construct the complex structure for evaluating the interaction between the protein and substrates, we tested molecular docking software such as LeDock and AutoDock Vina to dock the structure of At SuSy1 (PDB ID: 3S27, chain A) with its substrates.[31, 32] The docking results obtained by LeDock have a relatively good reproducibility to the crystal structure of At SuSy1, therefore, LeDock was further used to obtain the complex of Mc SuSy. UDP was first docked into the active site of Mc SuSy, resulting in the structure ofMc SuSy with UDP, which was then docked with sucrose. PyMOL (Version 2.4.1, Schrodinger LLC) was used to visualize and analyze the model structures generated, as well as to build illustrative figures.