Substrate dynamics in the active site of TfHex. A. Active site with docked natural substrate chitobiose 1 after 10 ns of molecular dynamics simulation. B. Overlay of the active sites of TfHex with docked GlcNAc (4) in the beginning of molecular dynamics (grey) and during stable period (vivid color). Tyr 470, which normally fixes the substrate’s acetamido-group by hydrogen bond with its oxygen, established new interaction with oxygen at C1-atom. C. Overlay of pNP-GalNAc (3, grey) and pNP-GlcNAc (2, vivid) in the active site of TfHex after 10 ns molecular dynamics. Common residues are in red circles, Arg 218 with 3 is not shown. D. Overlay of the active sites of TfHex with docked pNP-GlcNAc-uronate (5; vivid color, yellow color - hydrogen bonds) and pNP-GlcNAc (2; grey).