Abstract
Norlignans are a class of heartwood substances that accumulate in the heartwood of gymnosperms including Japanese cedar, hinoki cypress, and coast redwood. They are produced as phytoalexines in monocotyledons as well. We have elucidated that coumaryl coumarate is enzymatically transformed to hinokiresinol, but the protein that catalyzes the transformation remains to be elucidated. In this study, we identified the gene encoding the protein.
The protein (named as hinokiresinol syntahse) was purified from Asparagus cell cultures, and the protein contained two distinct polypeptides. The genes were cloned based on the partial amino acid sequences. Each ORF was expressed as recombinant protein in E. coli. Both recombinant proteins showed trans-hinokiresinol synthesizing activity. Surprisingly, the equimolar mixture of the proteins showed cis-hinokiresinol synthesizing activity. Considering that natural and recombinant hinokiresinol synthase are both dimers, it was strongly suggested that geometrical selectivity in hinokiresinol formation depends on the subunit composition of hinokiresinol synthase.
