Phyllactones F and G, Further Bis-Homoscalarane Sesterterpenes from the Sponge Phyllospongia Foliaseens

Introduction In the previous papers, we reported the isolation and structural elucidation of eight 20,24-bishomoscalarane sesterterpenes from the sponge Phyllospongia foliascens collected from Xisha Islands. As a result of our continual investigation of the same sponge

Bipolarins A–H, eight new ophiobolin-type sesterterpenes with antimicrobial activity from fungus Bipolaris sp. TJ403-B1

Bipolarins A–H(1–8), eight new tetracyclic ophiobolin-type sesterterpenes featuring a rare oxaspiro[4.4]nonane moiety, were isolated from cultures of fungus Bipolaris sp. TJ403-B1. Their structures and absolute configurations were elucidated by comprehensive spectroscopic analyses, single-crystal X-ray diffraction experiments, electronic circular dichroism and 13 C NMR calculations. Additionally, compound 5 exhibited significant selective antimicrobial activity against Enterococcus faecalis with an MIC value 8 μg·mL^-1.

Occurrence and biosynthesis of plant sesterterpenes (C25), a new addition to terpene diversity

Terpenes,the largest group of plant-specialized metabolites,have received considerable attention for their highly diverse biological activities.Monoterpenes(C10),sesquiterpenes(C15),diterpenes(C20),and triterpenes(C30)have been extensively investigated at both the biochemical and molecular levels over the past two decades.Sesterterpenes(C25),an understudied terpenoid group,were recently described by plant scientists at the molecular level.This review summarizes the plant species that produce sesterterpenes and describes recent developments in the field of sesterterpene biosynthesis,placing a special focus on the catalytic mechanism and evolution of geranylfarnesyl diphosphate synthase and sesterterpene synthase.Finally,we propose several questions to be addressed in future studies,which may help to elucidate sesterterpene metabolism in plants.

A NEW SESTERTERPENE FROM THE SPONGE PHYLLOSPONGIA FOLIASCENS

Phylloketal(1),a new sesterterpene which belongs to the scalarane class of sesterterpene.s with a 20,24- bishomo—tetracyclic skeleton,has been isolated from the South China Sea sponge Phyllospongia foliascens,and its structure was characterized mainly by one and two-dimensional NMR.

Phyllofenone A, a New Scalarane Sesterterpene from the Sponge Phyllospongia Foliascens(Pallas)

The present paper covers the structure of a new sesterterpene, phyllofenone A(1) , isolated from the South China Sea sponge Phyllospongia foliascens. Phyllofenone A is a member of the scalarane class of sesterterpenes with a (C-20, C-24)-bishomo-(C-25)-nortetra-cyclic skeleton. The structure charcterization was based on one- and two-dimensional NMR and mass spectroscopy with the assistance of molecular modeling. Phyllofenone A shows weak antifungal activity against Candida pseudotropicalis.

Expanding catalytic promiscuity of a bifunctional terpene synthase through a single mutation-induced change in hydrogen-bond network within the catalytic pocket

Fungal bifunctional terpene synthases(BFTSs)catalyze the formation of numerous di-/sester-/tri-terpenes skeletons.However,the mechanism in controlling the cyclization pattern of terpene scaffolds is rarely deciphered for further application of tuning the catalytic promiscuity of terpene synthases for expanding the chemical space.In this study,we expanded the catalytic promiscuity of Fusarium oxysporum fusoxypene synthase(FoFS)by a single mutation at L89,leading to the production of three new sesterterpenes.Further computational analysis revealed that the reconstitution of the hydrogen-bond(H-bond)network of second-shell residues around the active site of FoFS influences the orientation of the aromatic residue W69 within the first-shell catalytic pocket.Thus,the dynamic orientation of W69 alters the carbocation transport,leading to the production of diverse ring system skeletons.These findings enhance our knowledge on understanding the molecular mechanisms,which could be applied on protein engineering terpene synthases on regulating the terpene skeletons.

Heteromerization of short-chain trans-prenyltransferase controls precursor allocation within a plastidial terpenoid network

Terpenes are the largest and most diverse class of plant specialized metabolites.Sesterterpenes(C25),which are derived from the plastid methylerythritol phosphate pathway,were recently characterized in plants.In Arabidopsis thaliana,four genes encoding geranylfarnesyl diphosphate synthase(GFPPS)(AtGFPPS1 to 4)are responsible for the production of GFPP,which is the common precursor for sesterterpene biosynthesis.However,the interplay between sesterterpenes and other known terpenes remain elusive.Here,we first provide genetic evidence to demonstrate that GFPPSs are responsible for sesterterpene production in Arabidopsis.Blockage of the sesterterpene pathway at the GFPPS step increased the production of geranylgeranyl diphosphate(GGPP)-derived terpenes.Interestingly,co-expression of sester TPSs in GFPPSOE(overexpression)plants rescued the phenotypic changes of GFPPS-OE plants by restoring the endogenous GGPP.We further demonstrated that,in addition to precursor(DMAPP/IPP)competition by GFPPS and GGPP synthase(GGPPS)in plastids,GFPPS directly decreased the activity of GGPPS through protein-protein interaction,ultimately leading to GGPP deficiency in planta.Our study provides a new regulatory mechanism of the plastidial terpenoid network in plant cells.

Characterization of two chimeric sesterterpene synthases from a fungal symbiont isolated from a sesterterpenoid-producing Lamiaceae plant Leucosceptrum canum

Two chimeric sesterterpene synthases(Aa TPS1 and Aa TPS2)were functionally characterized from Alternaria alternata MB-30 isolated from the leaves of a sesterterpenoid-producing Lamiaceae plant Leucosceptrum canum.Aa TPS1 generated a 5/8/6/5 tetracyclic sesteraltererol(1)and its absolute stereochemistry was determined by X-ray crystallographic analysis of its derivative 10,11-epoxysesteraltererol(2),which enabled revision of the absolute configuration of C7 of sesterfisherol produced by Nf SS and PTTS014 characterized previously and its derivative 10,11-epoxysesterfisherol.Aa TPS2 produced a 5/15 bicyclic preterpestacin I(3).Site-directed mutagenesis suggested that F192 in Aa TPS1 was likely involved in controlling of the hydroxylation of C12,and eight amino acids were important for the enzyme activity of Aa TPS1 and Aa TPS2.The engineered Escherichia coli and Saccharomyces cerevisiae strains were constructed for the productions of compounds 1 and 3,and the highest titer of compound 1 reached 62.3 mg/L in shake-flask culture.Both compounds 1 and 2 showed anti-adipogenic activity.

Recently duplicated sesterterpene(C25) gene clusters in Arabidopsis thaliana modulate root microbiota

Land plants co-speciate with a diversity of continually expanding plant specialized metabolites(PSMs) and root microbial communities(microbiota).Homeostatic interactions between plants and root microbiota are essential for plant survival in natural environments.A growing appreciation of microbiota for plant health is fuelling rapid advances in genetic mechanisms of controlling microbiota by host plants.PSMs have long been proposed to mediate plant and single microbe interactions.However,the effects of PSMs,especially those evolutionarily new PSMs,on root microbiota at community level remain to be elucidated.Here,we discovered sesterterpenes in Arabidopsis thaliana,produced by recently duplicated prenyltransferase-terpene synthase(PT-TPS) gene clusters,with neo-functionalization.A single-residue substitution played a critical role in the acquisition of sesterterpene synthase(sesterTPS) activity in Brassicaceae plants.Moreover,we found that the absence of two root-specific sesterterpenoids,with similar chemical structure,significantly affected root microbiota assembly in similar patterns.Our results not only demonstrate the sensitivity of plant microbiota to PSMs but also establish a complete framework of host plants to control root microbiota composition through evolutionarily dynamic PSMs.

Molecular Basis for Sesterterpene Diversity Produced by Plant Terpene Synthases

Class I terpene synthase(TPS)generates bioactive terpenoids with diverse backbones.Sesterterpene synthase(sester-TPS,C25),a branch of class I TPSs,was recently identified in Brassicaceae.However,the catalytic mechanisms of sester-TPSs are not fully understood.Here,we first identified three nonclustered functional sester-TPSs(AtTPS06,AtTPS22,and AtTPS29)in Arabidopsis thaliana.AtTPS06 utilizes a type-B cyclization mechanism,whereas most other sester-TPSs produce various sesterterpene backbones via a type-A cyclization mechanism.We then determined the crystal structure of the AtTPS18–FSPP complex to explore the cyclization mechanism of plant sester-TPSs.We used structural comparisons and site-directed mutagenesis to further elucidate the mechanism:(1)mainly due to the outward shift of helix G,plant sester-TPSs have a larger catalytic pocket than do mono-,sesqui-,and di-TPSs to accommodate GFPP;(2)type-A sester-TPSs have more aromatic residues(five or six)in their catalytic pocket than classic TPSs(two or three),which also determines whether the type-A or type-B cyclization mechanism is active;and(3)the other residues responsible for product fidelity are determined by interconversion of AtTPS18 and its close homologs.Altogether,this study improves our understanding of the catalytic mechanism of plant sester-TPS,which ultimately enables the rational engineering of sesterterpenoids for future applications.