Isoprenoid Binding and Substrate Channeling in Drimenol Synthase, a Bifunctional Class II Terpene Cyclase-Phosphatase
More than one thousand bifunctional terpene synthases combining prenyltransferase and terpene cyclase activities have been identified in bacteria and fungi, but only a handful of enzymes have been identified that combine terpene cyclase activity with a downstream processing activity. Drimenol synthase from the marine bacterium Aquimarina spongiae (AsDMS) consists of a class II terpene cyclase…
Drimenol synthase, a bifunctional enzyme found in the marine bacterium Aquimarina spongiae, consists of two distinct domains: a class II terpene cyclase and a haloacid dehalogenase-like phosphatase. The cyclase domain transforms farnesyl diphosphate into drimenyl diphosphate, while the phosphatase domain hydrolyzes drimenyl diphosphate to produce the sesquiterpene alcohol, drimenol.
A recent study reported the first crystal structure of the enzyme, revealing crucial insights into the architecture of domain assembly and dimeric quaternary structure, providing a foundation for understanding the enzymatic mechanisms involved in cyclization and hydrolysis processes.
In this study, researchers further explored the enzyme's structure by generating a double mutant, D33A-D323A AsDMS, which was crystallized in complex with three different farnesyl diphosphate derivatives. These diphosphate groups bind tightly to the active sites of both the cyclase and phosphatase domains, with molecular recognition being a dominant interaction in both sites.
In the cyclase active site, only farnesyl diphosphate is long enough to bind adjacent to the catalytic general acid, initiating the cyclization cascade in the wild-type enzyme. However, the phosphatase active site accommodates all isoprenoid diphosphate groups, albeit with varying isoprenoid chain conformations.
These findings not only elucidate substrate recognition and catalysis in both active sites of Drimenol synthase, but also suggest the presence of substrate channeling in the wild-type enzyme. Substrate channeling refers to the direct transfer of a substrate from one enzyme active site to another, bypassing the need for release into the cellular environment.
This phenomenon could potentially enhance the efficiency of the enzymatic reaction and reduce energy expenditure. The crystal structures of Drimenol synthase, along with the kinetic evidence supporting substrate channeling, provide valuable insights into the enzyme's function and potential applications in biotechnology and drug discovery.
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