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Eunicellane diterpenoids, containing a typical 6,10-bicycle, are bioactive compounds widely present in marine corals, but rarely found in bacteria and plants. The intrinsic macrocycle exhibits innate structural flexibility resulting in dynamic conformational changes. However, the mechanisms controlling flexibility remain unknown. The discovery of a terpene synthase, MicA, that is responsible for the biosynthesis of a nearly non-flexible eunicellane skeleton, enable us to propose a feasible theory about the flexibility in eunicellane structures. Parallel studies of all eunicellane synthases in nature discovered to date, including 2Z-geranylgeranyl diphosphate incubations and density functional theory-based Boltzmann population computations, reveale that a trans-fused bicycle with a 2Z-configuration alkene restricts conformational flexibility resulting in a nearly non-flexible eunicellane skeleton. The catalytic route and the enzymatic mechanism of MicA are also elucidated by labeling experiments, density functional theory calculations, structural analysis of the artificial intelligence-based MicA model, and mutational studies., (© 2024. The Author(s).)

Biosynthetic modifications of the 6/10-bicyclic hydrocarbon skeletons of the eunicellane family of diterpenoids are unknown. We explored the biosynthesis of a bacterial trans -eunicellane natural product, albireticulone A ( 3 ), and identified a novel isomerase that catalyzes cryptic isomerization in the biosynthetic pathway. We also assigned functions of two cytochromes P450 that oxidize the eunicellane skeleton, one of which was a naturally evolved non-functional P450 that, when genetically repaired, catalyzes allylic oxidation. Finally, we described the chemical susceptibility of the trans -eunicellane skeleton to undergo Cope rearrangement to yield inseparable atropisomers.

The eunicellane diterpenoids are a unique family of natural products seen in marine organisms, plants, and bacteria. We used a series of biochemical, bioinformatics, and theoretical experiments to investigate the mechanism of the first diterpene synthase known to form the eunicellane skeleton. Deuterium labeling studies and quantum chemical calculations support that Bnd4, from Streptomyces sp. (CL12-4), forms the 6,10-bicyclic skeleton through a 1,10-cyclization, 1,3-hydride shift, and 1,14-cyclization cascade. Bnd4 also demonstrated sesquiterpene cyclase activity and the ability to prenylate small molecules. Bnd4 possesses a unique D 94 NxxxD motif and mutation experiments confirmed an absolute requirement for D94 as well as E169., (© 2021 Wiley-VCH GmbH.)

A new bicyclic diterpenoid, benditerpenoic acid, was isolated from soil-dwelling Streptomyces sp. (CL12-4). We sequenced the bacterial genome, identified the responsible biosynthetic gene cluster, verified the function of the terpene synthase, and heterologously produced the core diterpene. Comparative bioinformatics indicated this Streptomyces strain is phylogenetically unique and possesses nine terpene synthases. The absolute configurations of the new trans-fused bicyclo[8.4.0]tetradecanes were achieved by extensive spectroscopic analyses, including Mosher's analysis, J-based coupling analysis, and computations based on sparse NMR-derived experimental restraints. Interestingly, benditerpenoic acid exists in two distinct ring-flipped bicyclic conformations with a rotational barrier of ≈16 kcal mol -1 in solution. The diterpenes exhibit moderate antibacterial activity against Gram-positive bacteria including methicillin and multi-drug resistant Staphylococcus aureus. This is a rare example of an eunicellane-type diterpenoid from bacteria and the first identification of a diterpene synthase and biosynthetic gene cluster responsible for the construction of the eunicellane scaffold., (© 2021 Wiley-VCH GmbH.)

The eunicellane diterpenoids are a unique family of natural products seen in marine organisms, plants, and bacteria. We used a series of biochemical, bioinformatics, and theoretical experiments to investigate the mechanism of the first diterpene synthase known to form the eunicellane skeleton. Deuterium labeling studies and quantum chemical calculations support that Bnd4, from Streptomyces sp. (CL12-4), forms the 6,10-bicyclic skeleton through a 1,10-cyclization, 1,3-hydride shift, and 1,14-cyclization cascade. Bnd4 also demonstrated sesquiterpene cyclase activity and the ability to prenylate small molecules. Bnd4 possesses a unique D94 NxxxD motif and mutation experiments confirmed an absolute requirement for D94 as well as E169.

Ein neues bicyclisches Diterpenoid, Benditerpensäure, wurde aus einem im Erdreich vorkommenden Streptomyceten‐Stamm (CL12‐4) isoliert. Wir sequenzierten das Bakteriengenom, identifizierten den verantwortlichen Biosynthesegencluster, verifizierten die Funktion der Terpensynthase und produzierten heterolog das Diterpenoid‐Grundgerüst. Vergleichende Bioinformatik zeigte, dass dieser Streptomyceten‐Stamm phylogenetisch einzigartig ist und neun Terpensynthasen besitzt. Die absoluten Konfigurationen der neuen trans‐fusionierten Bicyclo[8.4.0]tetradecane wurden durch umfangreiche spektroskopische Analysen erreicht, einschließlich Moshers Analyse, NMR‐basierter Kopplungsanalyse, sowie DFT Berechnungen auf Basis von experimentellen NMR Parametern. Interessanterweise liegt Benditerpensäure in Lösung in zwei Ringkonformationen vor. Die Rotationsbarriere beträgt ca. 16 kcal mol−1. Die Diterpenoide zeigen mäßige antibakterielle Aktivität gegen Gram‐positive Bakterien, einschließlich Methicillin‐resistenten und multiresistenten Staphylococcus aureus. Hier präsentieren wir die erste Isolierung eines bakteriellen Eunicellan‐Diterpenoids und die Identifizierung der Diterpensynthase und des Biosynthesegenclusters, der für den Aufbau des bakteriellen Eunicellan‐Gerüsts verantwortlich ist. [ABSTRACT FROM AUTHOR]