1
|
Xu H, Dickschat JS. Germacrene A-A Central Intermediate in Sesquiterpene Biosynthesis. Chemistry 2020; 26:17318-17341. [PMID: 32442350 PMCID: PMC7821278 DOI: 10.1002/chem.202002163] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2020] [Revised: 05/20/2020] [Indexed: 01/17/2023]
Abstract
This review summarises known sesquiterpenes whose biosyntheses proceed through the intermediate germacrene A. First, the occurrence and biosynthesis of germacrene A in Nature and its peculiar chemistry will be highlighted, followed by a discussion of 6-6 and 5-7 bicyclic compounds and their more complex derivatives. For each compound the absolute configuration, if it is known, and the reasoning for its assignment is presented.
Collapse
Affiliation(s)
- Houchao Xu
- Kekulé-Institute for Organic Chemistry and BiochemistryUniversity of BonnGerhard-Domagk-Straße 153121BonnGermany
| | - Jeroen S. Dickschat
- Kekulé-Institute for Organic Chemistry and BiochemistryUniversity of BonnGerhard-Domagk-Straße 153121BonnGermany
| |
Collapse
|
2
|
Loizzi M, Miller DJ, Allemann RK. Silent catalytic promiscuity in the high-fidelity terpene cyclase δ-cadinene synthase. Org Biomol Chem 2019; 17:1206-1214. [PMID: 30652178 PMCID: PMC6369673 DOI: 10.1039/c8ob02821d] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Aza-analogues of carbocations inhibit δ-cadinene synthase: 1,6-cyclisation.
δ-Cadinene synthase (DCS) is a high-fidelity sesquiterpene synthase that generates δ-cadinene as the sole detectable organic product from its natural substrate (E,E)-FDP. Previous work with this enzyme using substrate analogues revealed the ability of DCS to catalyse both 1,10- and 1,6-cyclisations of substrate analogues. To test whether this apparent promiscuity was an artefact of alternate substrate use or an inherent property of the enzyme, aza analogues of the proposed α-bisabolyl cation intermediate were prepared since this cation would be formed after an initial 1,6-cyclisation of FDP. In the presence of 250 μM inorganic disphosphate both (R)- and (S)-aza-bisaboyl cations were potent competitive inhibitors of DCS (Ki = 2.5 ± 0.5 mM and 3.44 ± 1.43 μM, respectively). These compounds were also shown to be potent inhibitors of the 1,6-cyclase amorpha-4,11-diene synthase but not of the 1,10-cyclase aristolochene synthase from Penicillium roquefortii, demonstrating that the 1,6-cyclase activity of DCS is most likely an inherent property of the enzyme even when the natural substrate is used and not an artefact of the use of substrate analogues.
Collapse
Affiliation(s)
- Marianna Loizzi
- School of Chemistry, Cardiff University Main Building, Park Place, Cardiff, CF10 3AT, UK.
| | | | | |
Collapse
|
3
|
Suárez I, da Silva Lima G, Conti R, Pinedo C, Moraga J, Barúa J, de Oliveira ALL, Aleu J, Durán-Patrón R, Macías-Sánchez AJ, Hanson JR, Tallarico Pupo M, Hernández-Galán R, Collado IG. Structural and biosynthetic studies on eremophilenols related to the phytoalexin capsidiol, produced by Botrytis cinerea. PHYTOCHEMISTRY 2018; 154:10-18. [PMID: 29929021 DOI: 10.1016/j.phytochem.2018.06.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2018] [Revised: 06/11/2018] [Accepted: 06/12/2018] [Indexed: 06/08/2023]
Abstract
A thorough study of the fermentation broth of three strains of Botrytis cinerea which were grown on a modified Czapek-Dox medium supplemented with 5 ppm copper sulphate, yielded five undescribed metabolites. These metabolites possessed a sesquiterpenoid (+)-4-epi-eremophil-9-ene carbon skeleton which was enantiomeric to that of the phytoalexin, capsidiol. The isolation of these metabolites when the fungus was stressed, suggests that they may be potential effectors used by B. cinerea to circumvent plant chemical defences against phytopathogenic fungi. The biosynthesis of these compounds has been studied using 2H and 13C labelled acetate.
Collapse
Affiliation(s)
- Ivonne Suárez
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain
| | - Gesiane da Silva Lima
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain
| | - Raphael Conti
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain; Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, 14040-903 Ribeirão Preto, Brazil
| | - Cristina Pinedo
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain
| | - Javier Moraga
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain
| | - Javier Barúa
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain
| | - Ana Ligia L de Oliveira
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain; Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, 14040-903 Ribeirão Preto, Brazil
| | - Josefina Aleu
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain
| | - Rosa Durán-Patrón
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain
| | - Antonio J Macías-Sánchez
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain
| | - James R Hanson
- Department of Chemistry, University of Sussex, Brighton, Sussex, BN1 9QJ, United Kingdom
| | - Mônica Tallarico Pupo
- Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, 14040-903 Ribeirão Preto, Brazil
| | - Rosario Hernández-Galán
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain
| | - Isidro G Collado
- Departamento de Química Orgánica, Facultad de Ciencias, Campus Universitario Río San Pedro s/n, Torre sur, 4a planta, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain.
| |
Collapse
|
4
|
Abdelmagid WM, Adak T, Freeman JO, Tanner ME. Studies with Guanidinium- and Amidinium-Based Inhibitors Suggest Minimal Stabilization of Allylic Carbocation Intermediates by Dehydrosqualene and Squalene Synthases. Biochemistry 2018; 57:5591-5601. [PMID: 30179505 DOI: 10.1021/acs.biochem.8b00731] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Dehydrosqualene and squalene synthases catalyze the redox neutral and the reductive, head-to-head dimerization of farnesyl diphosphate, respectively. In each case, the reaction is thought to proceed via an initial dissociation of farnesyl diphosphate to form an allylic carbocation-pyrophosphate ion pair. This work describes the synthesis and testing of inhibitors in which a guanidinium or amidinium moiety is flanked by a phosphonylphosphinate group and a hydrocarbon tail. These functional groups bear a planar, delocalized, positive charge and therefore should act as excellent mimics of an allylic carbocation. An inhibitor bearing a neutral urea moiety was also prepared as a control. The positively charged inhibitors acted as competitive inhibitors against Staphylococcus aureus dehydrosqualene synthase with Ki values in the low micromolar range. Surprisingly, the neutral urea inhibitor was the most potent of the three. Similar trends were seen with the first half reaction of human squalene synthase. One interpretation of these results is that the active sites of these enzymes do not directly stabilize the allylic carbocation via electrostatic or π-cation interactions. Instead, it is likely that the enzymes use tight binding to the pyrophosphate and lipid moieties to promote catalysis and that electrostatic stabilization of the carbocation is provided by the bound pyrophosphate product. An alternate possibility is that these inhibitors cannot bind to the "ionization FPP-binding site" of the enzyme and only bind to the "nonionizing FPP-binding site". In either case, all reported attempts to generate potent inhibitors with cationic FPP analogues have been unsuccessful to date.
Collapse
Affiliation(s)
- Walid M Abdelmagid
- Department of Chemistry , University of British Columbia , Vancouver , British Columbia V6T 1Z1 , Canada
| | - Taniya Adak
- Department of Chemistry , University of British Columbia , Vancouver , British Columbia V6T 1Z1 , Canada
| | - Jon O Freeman
- Department of Chemistry , Pacific Lutheran University , Tacoma , Washington 98447 , United States
| | - Martin E Tanner
- Department of Chemistry , University of British Columbia , Vancouver , British Columbia V6T 1Z1 , Canada
| |
Collapse
|
5
|
Huynh F, Grundy DJ, Jenkins RL, Miller DJ, Allemann RK. Sesquiterpene Synthase-Catalysed Formation of a New Medium-Sized Cyclic Terpenoid Ether from Farnesyl Diphosphate Analogues. Chembiochem 2018; 19:1834-1838. [PMID: 29802753 PMCID: PMC6334173 DOI: 10.1002/cbic.201800218] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2018] [Indexed: 11/08/2022]
Abstract
Terpene synthases catalyse the first step in the conversion of prenyl diphosphates to terpenoids. They act as templates for their substrates to generate a reactive conformation, from which a Mg2+ -dependent reaction creates a carbocation-PPi ion pair that undergoes a series of rearrangements and (de)protonations to give the final terpene product. This tight conformational control was exploited for the (R)-germacrene A synthase- and germacradien-4-ol synthase-catalysed formation of a medium-sized cyclic terpenoid ether from substrates containing nucleophilic functional groups. Farnesyl diphosphate analogues with a 10,11-epoxide or an allylic alcohol were efficiently converted to a 11-membered cyclic terpenoid ether that was characterised by HRMS and NMR spectroscopic analyses. Further experiments showed that other sesquiterpene synthases, including aristolochene synthase, δ-cadinene synthase and amorphadiene synthase, yielded this novel terpenoid from the same substrate analogues. This work illustrates the potential of terpene synthases for the efficient generation of structurally and functionally novel medium-sized terpene ethers.
Collapse
Affiliation(s)
- Florence Huynh
- School of ChemistryCardiff UniversityMain BuildingPark PlaceCardiffCF10 3ATUK
| | - Daniel J. Grundy
- School of ChemistryCardiff UniversityMain BuildingPark PlaceCardiffCF10 3ATUK
| | - Robert L. Jenkins
- School of ChemistryCardiff UniversityMain BuildingPark PlaceCardiffCF10 3ATUK
| | - David J. Miller
- School of ChemistryCardiff UniversityMain BuildingPark PlaceCardiffCF10 3ATUK
| | - Rudolf K. Allemann
- School of ChemistryCardiff UniversityMain BuildingPark PlaceCardiffCF10 3ATUK
| |
Collapse
|
6
|
Abstract
![]()
The
year 2017 marks the twentieth anniversary of terpenoid cyclase
structural biology: a trio of terpenoid cyclase structures reported
together in 1997 were the first to set the foundation for understanding
the enzymes largely responsible for the exquisite chemodiversity of
more than 80000 terpenoid natural products. Terpenoid cyclases catalyze
the most complex chemical reactions in biology, in that more than
half of the substrate carbon atoms undergo changes in bonding and
hybridization during a single enzyme-catalyzed cyclization reaction.
The past two decades have witnessed structural, functional, and computational
studies illuminating the modes of substrate activation that initiate
the cyclization cascade, the management and manipulation of high-energy
carbocation intermediates that propagate the cyclization cascade,
and the chemical strategies that terminate the cyclization cascade.
The role of the terpenoid cyclase as a template for catalysis is paramount
to its function, and protein engineering can be used to reprogram
the cyclization cascade to generate alternative and commercially important
products. Here, I review key advances in terpenoid cyclase structural
and chemical biology, focusing mainly on terpenoid cyclases and related
prenyltransferases for which X-ray crystal structures have informed
and advanced our understanding of enzyme structure and function.
Collapse
Affiliation(s)
- David W Christianson
- Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, United States
| |
Collapse
|
7
|
Lledó A, Soler A. Binding of ion pairs in a thiourea-functionalized self-folding cavitand. Org Chem Front 2017. [DOI: 10.1039/c7qo00191f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A bioinspired supramolecular container with complementary binding sites displays cooperative binding of ion pairs.
Collapse
Affiliation(s)
- A. Lledó
- Institute of Computational Chemistry and Catalysis and Department of Chemistry
- Universitat de Girona
- 17003 Girona
- Spain
| | - A. Soler
- Institute of Computational Chemistry and Catalysis and Department of Chemistry
- Universitat de Girona
- 17003 Girona
- Spain
| |
Collapse
|
8
|
Faraldos JA, Grundy DJ, Cascon O, Leoni S, van der Kamp MW, Allemann RK. Enzymatic synthesis of natural (+)-aristolochene from a non-natural substrate. Chem Commun (Camb) 2016; 52:14027-14030. [DOI: 10.1039/c6cc08164a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Aristolochene synthase from Penicillium roqueforti converts 7-methylene-FDP, a substrate the enzyme never encounters in nature, to the natural product (+)-aristolochene.
Collapse
Affiliation(s)
| | | | - Oscar Cascon
- School of Chemistry
- Cardiff University
- Cardiff CF10 3AT
- UK
| | - Stefano Leoni
- School of Chemistry
- Cardiff University
- Cardiff CF10 3AT
- UK
| | - Marc W. van der Kamp
- School of Biochemistry
- Faculty of Biomedical Sciences & Centre for Computational Chemistry
- School of Chemistry
- University of Bristol
- Biomedical Sciences Building
| | | |
Collapse
|
9
|
Vardakou M, Salmon M, Faraldos JA, O’Maille PE. Comparative analysis and validation of the malachite green assay for the high throughput biochemical characterization of terpene synthases. MethodsX 2014; 1:187-96. [PMID: 26150952 PMCID: PMC4472957 DOI: 10.1016/j.mex.2014.08.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Accepted: 08/15/2014] [Indexed: 11/21/2022] Open
Abstract
Terpenes are the largest group of natural products with important and diverse biological roles, while of tremendous economic value as fragrances, flavours and pharmaceutical agents. Class-I terpene synthases (TPSs), the dominant type of TPS enzymes, catalyze the conversion of prenyl diphosphates to often structurally diverse bioactive terpene hydrocarbons, and inorganic pyrophosphate (PPi). To measure their kinetic properties, current bio-analytical methods typically rely on the direct detection of hydrocarbon products by radioactivity measurements or gas chromatography-mass spectrometry (GC-MS). In this study we employed an established, rapid colorimetric assay, the pyrophosphate/malachite green assay (MG), as an alternative means for the biochemical characterization of class I TPSs activity.•We describe the adaptation of the MG assay for turnover and catalytic efficiency measurements of TPSs.•We validate the method by direct comparison with established assays. The agreement of k cat/K M among methods makes this adaptation optimal for rapid evaluation of TPSs.•We demonstrate the application of the MG assay for the high-throughput screening of TPS gene libraries.
Collapse
Affiliation(s)
- Maria Vardakou
- Department of Metabolic Biology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom
| | - Melissa Salmon
- Department of Metabolic Biology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom
| | - Juan A. Faraldos
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, United Kingdom
| | - Paul E. O’Maille
- Department of Metabolic Biology, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom
- Food and Health Programme, Institute of Food Research, Norwich Research Park, Norwich NR4 7UA, United Kingdom
| |
Collapse
|
10
|
Chen M, Al-lami N, Janvier M, D'Antonio EL, Faraldos JA, Cane DE, Allemann RK, Christianson DW. Mechanistic insights from the binding of substrate and carbocation intermediate analogues to aristolochene synthase. Biochemistry 2013; 52:5441-53. [PMID: 23905850 PMCID: PMC3755762 DOI: 10.1021/bi400691v] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Aristolochene synthase, a metal-dependent sesquiterpene cyclase from Aspergillus terreus, catalyzes the ionization-dependent cyclization of farnesyl diphosphate (FPP) to form the bicyclic eremophilane (+)-aristolochene with perfect structural and stereochemical precision. Here, we report the X-ray crystal structure of aristolochene synthase complexed with three Mg(2+) ions and the unreactive substrate analogue farnesyl-S-thiolodiphosphate (FSPP), showing that the substrate diphosphate group is anchored by metal coordination and hydrogen bond interactions identical to those previously observed in the complex with three Mg(2+) ions and inorganic pyrophosphate (PPi). Moreover, the binding conformation of FSPP directly mimics that expected for productively bound FPP, with the exception of the precise alignment of the C-S bond with regard to the C10-C11 π system that would be required for C1-C10 bond formation in the first step of catalysis. We also report crystal structures of aristolochene synthase complexed with Mg(2+)3-PPi and ammonium or iminium analogues of bicyclic carbocation intermediates proposed for the natural cyclization cascade. Various binding orientations are observed for these bicyclic analogues, and these orientations appear to be driven by favorable electrostatic interactions between the positively charged ammonium group of the analogue and the negatively charged PPi anion. Surprisingly, the active site is sufficiently flexible to accommodate analogues with partially or completely incorrect stereochemistry. Although this permissiveness in binding is unanticipated, based on the stereochemical precision of catalysis that leads exclusively to the (+)-aristolochene stereoisomer, it suggests the ability of the active site to enable controlled reorientation of intermediates during the cyclization cascade. Taken together, these structures illuminate important aspects of the catalytic mechanism.
Collapse
Affiliation(s)
- Mengbin Chen
- Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, 19104-6323 USA
| | - Naeemah Al-lami
- School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, Wales, United Kingdom
| | - Marine Janvier
- School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, Wales, United Kingdom
| | - Edward L. D'Antonio
- Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, 19104-6323 USA
| | - Juan A. Faraldos
- School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, Wales, United Kingdom
| | - David E. Cane
- Department of Chemistry, Box H, Brown University, Providence, RI 02912-9108 USA
| | - Rudolf K. Allemann
- School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, Wales, United Kingdom
| | - David W. Christianson
- Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, 19104-6323 USA,To whom correspondence should be addressed: Department of Chemistry, University of Pennsylvania, 2001 Roy and Diana Vagelos Laboratories, 231 South 34th Street, Philadelphia, PA, 19104-6323 USA. Tel: 215-898-5714;
| |
Collapse
|
11
|
Kang JY, Carter RG. Primary Amine, Thiourea-Based Dual Catalysis Motif for Synthesis of Stereogenic, All-Carbon Quaternary Center-Containing Cycloalkanones. Org Lett 2012; 14:3178-81. [DOI: 10.1021/ol301272r] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jun Yong Kang
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, United States
| | - Rich G. Carter
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, United States
| |
Collapse
|
12
|
Faraldos JA, Miller DJ, González V, Yoosuf-Aly Z, Cascón O, Li A, Allemann RK. A 1,6-ring closure mechanism for (+)-δ-cadinene synthase? J Am Chem Soc 2012; 134:5900-8. [PMID: 22397618 DOI: 10.1021/ja211820p] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Recombinant (+)-δ-cadinene synthase (DCS) from Gossypium arboreum catalyzes the metal-dependent cyclization of (E,E)-farnesyl diphosphate (FDP) to the cadinane sesquiterpene δ-cadinene, the parent hydrocarbon of cotton phytoalexins such as gossypol. In contrast to some other sesquiterpene cyclases, DCS carries out this transformation with >98% fidelity but, as a consequence, leaves no mechanistic traces of its mode of action. The formation of (+)-δ-cadinene has been shown to occur via the enzyme-bound intermediate (3R)-nerolidyl diphosphate (NDP), which in turn has been postulated to be converted to cis-germacradienyl cation after a 1,10-cyclization. A subsequent 1,3-hydride shift would then relocate the carbocation within the transient macrocycle to expedite a second cyclization that yields the cadinenyl cation with the correct cis stereochemistry found in (+)-δ-cadinene. An elegant 1,10-mechanistic pathway that avoids the formation of (3R)-NDP has also been suggested. In this alternative scenario, the final cadinenyl cation is proposed to be formed through the intermediacy of trans, trans-germacradienyl cation and germacrene D. In addition, an alternative 1,6-ring closure mechanism via the bisabolyl cation has previously been envisioned. We report here a detailed investigation of the catalytic mechanism of DCS using a variety of mechanistic probes including, among others, deuterated and fluorinated FDPs. Farnesyl diphosphate analogues with fluorine at C2 and C10 acted as inhibitors of DCS, but intriguingly, after prolonged overnight incubations, they yielded 2F-germacrene(s) and a 10F-humulene, respectively. The observed 1,10-, and to a lesser extent, 1,11-cyclization activity of DCS with these fluorinated substrates is consistent with the postulated macrocyclization mechanism(s) en route to (+)-δ-cadinene. On the other hand, mechanistic results from incubations of DCS with 6F-FPP, (2Z,6E)-FDP, neryl diphosphate, 6,7-dihydro-FDP, and NDP seem to be in better agreement with the potential involvement of the alternative biosynthetic 1,6-ring closure pathway. In particular, the strong inhibition of DCS by 6F-FDP, coupled to the exclusive bisabolyl- and terpinyl-derived product profiles observed for the DCS-catalyzed turnover of (2Z,6E)-farnesyl and neryl diphosphates, suggested the intermediacy of α-bisabolyl cation. DCS incubations with enantiomerically pure [1-(2)H(1)](1R)-FDP revealed that the putative bisabolyl-derived 1,6-pathway proceeds through (3R)-nerolidyl diphosphate (NDP), is consistent with previous deuterium-labeling studies, and accounts for the cis stereochemistry characteristic of cadinenyl-derived sesquiterpenes. While the results reported here do not unambiguously rule in favor of 1,6- or 1,10-cyclization, they demonstrate the mechanistic versatility inherent to DCS and highlight the possible existence of multiple mechanistic pathways.
Collapse
Affiliation(s)
- Juan A Faraldos
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, United Kingdom
| | | | | | | | | | | | | |
Collapse
|
13
|
Faraldos JA, Gonzalez V, Allemann RK. The role of aristolochene synthase in diphosphate activation. Chem Commun (Camb) 2012; 48:3230-2. [PMID: 22349314 DOI: 10.1039/c2cc17588f] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Analysis of the role of amino acids involved in diphosphate binding in the Michaelis complex of aristolochene synthase from P. roqueforti (PR-AS) reveals mechanistic details about leaving group (PPi) activation and the nature of the active site acid.
Collapse
Affiliation(s)
- Juan A Faraldos
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK
| | | | | |
Collapse
|
14
|
Miller DJ, Allemann RK. Sesquiterpene synthases: Passive catalysts or active players? Nat Prod Rep 2012; 29:60-71. [DOI: 10.1039/c1np00060h] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
15
|
Cascón O, Touchet S, Miller DJ, Gonzalez V, Faraldos JA, Allemann RK. Chemoenzymatic preparation of germacrene analogues. Chem Commun (Camb) 2012; 48:9702-4. [DOI: 10.1039/c2cc35542f] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
16
|
Faraldos JA, González V, Senske M, Allemann RK. Templating effects in aristolochene synthase catalysis: elimination versus cyclisation. Org Biomol Chem 2011; 9:6920-3. [PMID: 21870004 DOI: 10.1039/c1ob06184d] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Analysis of the products generated by mutants of aristolochene synthase from P. roqueforti (PR-AS) revealed the prominent structural role played by the aliphatic residue Leu 108 in maintaining the productive conformation of farnesyl diphosphate to ensure C1-C10 (σ-bond) ring-closure and hence (+)-aristolochene production.
Collapse
Affiliation(s)
- Juan A Faraldos
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, United Kingdom
| | | | | | | |
Collapse
|
17
|
Faraldos JA, Antonczak AK, González V, Fullerton R, Tippmann EM, Allemann RK. Probing eudesmane cation-π interactions in catalysis by aristolochene synthase with non-canonical amino acids. J Am Chem Soc 2011; 133:13906-9. [PMID: 21815676 DOI: 10.1021/ja205927u] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Stabilization of the reaction intermediate eudesmane cation (3) through interaction with Trp 334 during catalysis by aristolochene synthase from Penicillium roqueforti was investigated by site-directed incorporation of proteinogenic and non-canonical aromatic amino acids. The amount of germacrene A (2) generated by the mutant enzymes served as a measure of the stabilization of 3. 2 is a neutral intermediate, from which 3 is formed during PR-AS catalysis by protonation of the C6,C7 double bond. The replacement of Trp 334 with para-substituted phenylalanines of increasing electron-withdrawing properties led to a progressive accumulation of 2 that showed a good correlation with the interaction energies of simple cations such as Na(+) with substituted benzenes. These results provide compelling evidence for the stabilizing role played by Trp 334 in aristolochene synthase catalysis for the energetically demanding transformation of 2 to 3.
Collapse
Affiliation(s)
- Juan A Faraldos
- School of Chemistry, Cardiff University, Park Place, Cardiff, United Kingdom
| | | | | | | | | | | |
Collapse
|
18
|
Faraldos JA, Allemann RK. Inhibition of (+)-aristolochene synthase with iminium salts resembling eudesmane cation. Org Lett 2011; 13:1202-5. [PMID: 21271717 DOI: 10.1021/ol2000843] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Trigonal iminium halides of (4aS,7S)-1,4a-dimethyl- and (4aS,7S)-4a-methyl-7-(prop-1-en-2-yl)-2,3,4,4a,5,6,7,8-octahydroquinolinium ions, aimed to mimic transition states associated with the aristolochene synthase-catalyzed cyclization of (-)-germacrene A to eudesmane cation, were evaluated under standard kinetic steady-state conditions. In the presence of inorganic diphosphate, these analogues were shown to competitively inhibit the enzyme, suggesting a stabilizing role for the diphosphate leaving group in this apparently endothermic transformation.
Collapse
Affiliation(s)
- Juan A Faraldos
- School of Chemistry, Cardiff University, Cardiff, United Kingdom
| | | |
Collapse
|
19
|
Zhou K, Peters RJ. Electrostatic effects on (di)terpene synthase product outcome. Chem Commun (Camb) 2011; 47:4074-80. [PMID: 21305070 DOI: 10.1039/c0cc02960b] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Terpene synthases catalyze complex reactions, often forming multiple chiral centers in cyclized olefin products from acyclic allylic diphosphate precursors, yet have been suggested to largely control their reactions via steric effects, serving as templates. However, recent results highlight electrostatic effects also exerted by these enzymes. Perhaps not surprisingly, the pyrophosphate co-product released in the initiating and rate-limiting chemical step provides an obvious counter-ion that may steer carbocation migration towards itself. This is emphasized by the striking effects of a recently uncovered single residue switch for diterpene synthase product outcome, whereby substitution of hydroxyl residues for particular aliphatic residues has been shown to be sufficient to "short-circuit" complex cyclization and/or rearrangement reactions, with the converse change further found to be sufficient to increase reaction complexity. The mechanistic hypothesis for the observed effects is hydroxyl dipole stabilization of the specific carbocation formed by initial cyclization, enabling deprotonation of this early intermediate, whereas the lack of such stabilization (i.e. in the presence of an aliphatic side chain) leads to carbocation migration towards the pyrophosphate co-product, resulting in a more complex reaction. This is further consistent with the greater synergy exhibited between pyrophosphate and aza-analogs of late, relative to early, stage carbocation intermediates, and crystallographic analysis of the monoterpene cyclase bornyl diphosphate synthase wherein mechanistically non-relevant counter-ion pairing between aza-analogs of early stage carbocation intermediates and pyrophosphate is observed. Thus, (di)terpene synthases seem to mediate specific reaction outcomes, at least in part, by providing electrostatic effects to counteract those exerted by the pyrophosphate co-product.
Collapse
Affiliation(s)
- Ke Zhou
- Department of Biochemistry, Biophysics, & Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | | |
Collapse
|
20
|
|