Fig. 5: Crystal structures of LbUGT1 and LbUGT3 and their regioselectivity analysis.

A Proposed catalytic mechanism for di-glycosylation of LbUGT1 and LbUGT3; B, C The crystal structures of LbUGT1/UDP and LbUGT3/UDP with the N-sugar acceptor binding domain (green and slate) and C-sugar donor binding domain (limon and gray). The UDP is shown as yellow sticks; D Overlay of LbUGT1/UDP and LbUGT3/UDP. Residues are color-coded as in B. C But the difference for the putative entry region colored in red and blue, respectively; E, F The active-site pockets of LbUGT1 and LbUGT3 with the common substrate 2 shown in cyan and UDP-Glc shown in yellow. The active-site pockets are shown in electrostatic surface representation (the negatively charged regions are shown in red, the positively charged regions are shown in blue and the hydrophobic regions are shown in white), the residues located within the circled region are colored as green sticks, residues His are represented by a red star; G Superposition of LbUGT3-2 (residues and UDP-Glc, gray; 2, salmon) with LbUGT3-8 (residues and UDP-Glc, green; 8, cyan). The hydrogen bonds were shown with the purple dash; H The active-site pocket of LbUGT3 with 8 (residues, green; UDP-Glc, yellow; 8, cyan; hydrogen bonds, gray dash); I In vitro assay of the mutants of LbUGT1/3 using 2 as substrate. Data represent mean ± SD (n = 3). The source data underlying Fig. 5I are provided in a Source Data file.