Fig. 4

Putative mechanism of DAPDH catalysis and docking analysis of CgDAPDH^BC621-NADP⁺ with D-HPG. a A schematic view of the DAPDH reduction mechanism adapted to DAP. The hydride transfer from DAP (C4H) to NADP⁺ (C4N) is marked as pink spheres, the C6 of imino acid intermediate attacked by water and the ND1 of H152 are marked as blue spheres. b Two key distances in reductive amination process. The yellow dash lines denote d_{(C6HDAP−C4NNADP)} and d_{(C6DAP−ND1His152)}, respectively. NADP⁺ cofactor is shown in cyan, DAP is shown in orange, and residue H152 is shown in green. c A detailed active site view of CgDAPDH^BC621-NADP⁺ with D-HPG. D-HPG is shown in purple, residue W119 is shown in orange, W144 is shown in light pink, I169 is shown in magenta, and Y223 is shown in yellow. d The interactions between D-HPG and CgDAPDH^BC621 and the two key distance values. The green dash lines denote hydrogen-bond interactions and the cyan dash line denote π–π stacking interaction. Residue D120 is shown in orange, L150 is shown in magenta, G151 is shown in yellow, and N270 is shown in white