Decoding Catalysis by Terpene Synthases

Abstract

The review by Christianson, published in 2017 on the twentieth anniversary of the emergence of the field, summarizes the foundational discoveries and key advances in terpene synthase/cyclase (TS) biocatalysis (Christianson, D. W. Chem Rev 2017, 117 (17), 11570–11648. DOI: 10.1021/acs.chemrev.7b00287). Here, we review the TS literature published since then, bringing the field up to date and looking forward to what could be the near future of TS rational design. Many revealing discoveries have been made in recent years, building on the knowledge and fundamental principles uncovered during those initial two decades of study. We use these to explore TS reaction chemistry and see how a combined experimental and computational approach helps to decipher the complexities of TS catalysis. Revealed are a suite of catalytic motifs which control product outcome in TSs, some obvious, some more subtle. We examine each in detail, using the most recent papers and insights to illustrate how exactly this fascinating class of enzymes takes a single acyclic substrate and turns it into the many thousands of complex terpenoids found in Nature. We then explore some of the recent strategies for TS engineering, including machine learning and other data-driven approaches. From this, rational and predictive engineering of TSs, “designer terpene synthases”, will begin to emerge as a realistic goal.

Structure-Based Engineering of a Sesquiterpene Cyclase to Generate an Alcohol Product: Conversion of epi-Isozizaene Synthase into α-Bisabolol Synthase

“…Comparison with a naturally occurring α-bisabolol synthase reveals common active site features, thereby demonstrating significant potential for structure-based approaches to reprogramming isoprenoid cyclization cascades. These results reinforce the idea that one need not be limited to naturally occurring cyclases for the generation of desired terpene products, e.g., as applications in synthetic biology are considered. ,, Our continuing efforts to expand the product repertoire of EIZS will be reported in due course.…”

“…Terpene natural products are secondary (a.k.a. specialized) metabolites that are found in all domains of life. − Despite the extraordinarily diverse array of hydrocarbon skeletons that continue to be discovered in this family of more than 102,000 natural products, all derive from a mere handful of simple isoprenoid precursors. − This remarkable chemodiversity is largely attributed to the activity of terpene cyclases, enzymes that catalyze multistep reaction sequences that transform linear isoprenoid substrates into structurally complex products typically containing one or more rings and stereocenters. − Notably, terpenoid natural products have been essential components of the pharmacopeia since times of antiquity. For example, myrrh was used by Hippocrates (470–377 B.C.E.)…”

“…The three-dimensional contour of a terpene cyclase active site serves as a template for catalysis by chaperoning the conformation of a flexible isoprenoid substrate required to generate a specific product. − Following ionization of the enzyme-bound substrate, the hallmark of a terpene cyclase reaction is a highly controlled progression of multiple high-energy carbocation intermediates leading to the final product. Aromatic residues largely define the active site contour and stabilize these intermediates and their flanking transition states through cation−π interactions.…”

Functional and Mechanistic Characterization of the 4,5‐diepi‐Isoishwarane Synthase from the Liverwort Radula lindenbergiana

“…Terpene synthases are remarkable enzymes that catalyze some of the most complex transformations in natural product biosynthesis. [1][2][3] The type I of these enzymes [4] acts on an acyclic oligoprenyl diphosphate precursor such as geranyl diphosphate (GPP, towards monoterpenes), [5] farnesyl diphosphate (FPP, sesquiterpenes), [6] geranylgeranyl diphosphate (GGPP, diterpenes), [7] geranylfarnesyl diphosphate (GFPP, sesterterpenes), [8] or even farnesylfarnesyl diphosphate (FFPP, non-squalene derived triterpenes), [9] and converts it by the abstraction of diphosphate and through a cationic cascade reaction into a structurally complex, often polycyclic terpene hydrocarbon or alcohol. These compounds are formed in termination steps involving either a deprotonation or quenching of a cationic intermediate with water.…”

Mechanistic characterisation of a sesquiterpene synthase for asterisca-1,6-diene from the liverwort Radula lindenbergiana and implications for pentalenene biosynthesis

“…Terpene synthases are fascinating biocatalysts that can convert acyclic and achiral oligoprenyl diphosphates such as geranyl diphosphate (GPP), farnesyl diphosphate (FPP), geranylgeranyl diphosphate (GGPP), geranylfarnesyl diphosphate (GFPP) and even farnesylfarnesyl diphosphate (FFPP) into structurally complex terpene hydrocarbons or alcohols. [1][2][3][4][5] The products of these enzymatic reactions are usually chiral and formed with a high enantioselectivity, may contain several stereogenic centres, and are often polycyclic. During the terpene synthase reaction the majority of the carbons of the substrate may encounter a change in the bonding situation which makes terpene cyclisations one of the most complex transformations in nature.…”