In the structure of IPO-Me-Man, two IPO protomers were built, and only one Me-Man molecule could be observed in chain A. The temperature factor of Me-Man in the structure of IPO-Me-Man is 66.5 Å 2 , which is higher than that of Me-Glc, with 34.5 Å 2 (Table 1) . This phenomenon might indicate that only a few Me-Man molecules bound to IPO proteins in IPO-Me-Man, which resulted in a higher temperature factor. Nine hydrogen bonds are formed by the residues Gly21, Tyr97, Gly141, Trp142, Tyr143, and Asp145 of IPO and the atoms O1, O3, O4, O5 and O6 of Me-Man ( Figure 3C and Table 1 ). The atom C7 of Me-Man is also involved in the Me…p interaction with Trp142 of IPO. The binding orientation of Me-Man is similar to that of Me-Glc. In the structure IPO-Me-Gal, 10 hydrogen bonds are formed by the same residues Gly21, Tyr97, Gly141, Trp142, Tyr143, and Asp145 of IPO ( Figure 3D and Table 1 ). The atom C7 of Me-Gal is shown in the Me…p interaction with Trp142 of IPO. This revealed the importance of the methyl group of carbohydrates for binding to IPO.