Dihydroxy Terpene Synthase: Spatiotemporally Precise Manipulation of Water-Mediated Dihydroxylation via Stepwise Quenching of Carbocations

Biosynthesis of hydroxy terpenes, which possess better solubility and target-binding capability than terpene hydrocarbons, generally needs cascaded catalysis of terpene synthase (TS) and cytochrome P450 oxygenase. Interestingly, some TSs can directly generate hydroxy terpenes (mostly monohydroxy terpenes) independent of oxygenases. There are even rare TSs that can form dihydroxy terpenes directly. Nevertheless, the structure and catalytic mechanism of dihydroxy terpene synthases (DHTSs) remain elusive to date, hindering their practical applications. Through protein crystallography, multiscale simulations, and site-directed mutagenesis, we elucidate a stepwise carbocation quenching mechanism. In this process, two water molecules are strictly manipulated by a dynamic hydrogen-bond network to quench the carbocation intermediates. Most importantly, Tyr312 was identified as the indispensable and irreplaceable residue for initiating the reprotonation of the monohydroxy terpene. The spatiotemporally precise manipulation mechanism of DHTSs enriches the knowledge of TSs and lays a foundation for developing an oxygenase-independent biosynthesis system of multihydroxy terpenes.