Fig. 5: Inverted acceptor substrate binding modes of HsCPTa and HsCPTb.

Simulation included the aspartate-mediated coordination of Mg²⁺ ions (spheres), the interacting pyrophosphate moiety (orange), and the dissociated isoprenyl residue (turquoise) (for details of the conserved donor substrate binding, see Supplementary Fig. 20). a, b Inverted binding poses of acceptor substrate 1 in the active site cavities of HsCPTa (green) and HsCPTb (red). The two C-3 gem-prenyl residues involved in the reactions are distinguished by light and deep blue colours. Steric hindrance is introduced by the trans-like conformation of the benzoyl (C-1) and prenyl groups (C-5) with respect to the phloroglucinol ring plane, leading to the regiospecific ring closure reactions. c Docking of acceptor substrate 2 into the HsCPTa pocket allows the same reaction principle, which is not affected by the elongated geranyl group (deep blue). d In the inverted binding mode of HsCPTb, the upward-facing geranyl chain interferes with the binding of the donor substrate, preventing the reaction from proceeding. White surface, binding cavity; dashed red arrows, reaction sequence; dashed yellow lines, distance measure in Å.