Pinoresinol-lariciresinol reductase: Substrate versatility, enantiospecificity, and kinetic properties.

Two western red cedar pinoresinol-lariciresinol reductase (PLR) homologues were studied to determine their enantioselective, substrate versatility, and kinetic properties. PLRs are downstream of dirigent protein engendered, coniferyl alcohol derived, stereoselective coupling to afford entry into the 8- and 8'-linked furofuran lignan, pinoresinol. Our investigations showed that each PLR homolog can enantiospecifically metabolize different furofuran lignans with modified aromatic ring substituents, but where phenolic groups at both C4/C4' are essential for catalysis. These results are consistent with quinone methide intermediate formation in the PLR active site. Site-directed mutagenesis and kinetic measurements provided additional insight into factors affecting enantioselectivity and kinetic properties. From these data, PLRs can be envisaged to allow for the biotechnological potential of generation of various lignan skeleta, that could be differentially "decorated" on their aromatic ring substituents, via the action of upstream dirigent proteins.