Structural highlights
Function
[ASR6_SARSH] Alpha-humulene synthase; part of the gene cluster that mediates the biosynthesis of xenovulene A, an unusual meroterpenoid that has potent inhibitory effects on the human gamma-aminobutyrate A (GABAA) benzodiazepine receptor (PubMed:29773797). The first step of xenovulene A biosynthesis is the biosynthesis of 3-methylorcinaldehyde performed by the non-reducing polyketide synthase aspks1 (PubMed:17912413, PubMed:29773797, PubMed:20552126). The salicylate hydroxylase asL1 then catalyzes the oxidative dearomatization of 3-methylorcinaldehyde to yield a dearomatized hydroxycyclohexadione (PubMed:29773797). The 2-oxoglutarate-dependent dioxygenase asL3 further catalyzes the oxidative ring expansion to provide the first tropolone metabolite (PubMed:29773797). The cytochrome P450 monooxygenase asR2 allows the synthesis of tropolone hemiacetal (PubMed:29773797). In parallel, a previously unrecognised class of terpene cyclase, asR6, produces alpha-humulene from farnesylpyrophosphate (FPP) (PubMed:29773797). The putative Diels-Alderase asR5 probably catalyzes the formation of the tropolone-humulene skeleton by linking humulene and the polyketide moiety (PubMed:29773797). Oxidative-ring contractions catalyzed by asL4 and asL6 then processively remove carbon atoms from the polyketide to yield xenovulene A (PubMed:29773797).[1] [2] [3]
Publication Abstract from PubMed
The non-canonical terpene cyclase AsR6 is responsible for the formation of 2E,6E,9E-humulene during the biosynthesis of the tropolone sesquiterpenoid (TS) xenovulene A. The structures of unliganded AsR6 and of AsR6 in complex with an in crystallo cyclized reaction product and thiolodiphosphate reveal a new farnesyl diphosphate binding motif that comprises a unique binuclear Mg2+cluster and an essential K289 residue that is conserved in all humulene synthases involved in TS formation. Structure-based sitedirected mutagenesis of AsR6 and its homologue EupR3 identify a single residue, L285/M261, that controls the production of either 2E,6E,9E- or 2Z,6E,9E-humulene. A possible mechanism for the observed stereoselectivity was investigated using different isoprenoid precursors and results demonstrate that M261 has gatekeeping control over product formation.
Understanding and Engineering the Stereoselectivity of Humulene Synthase.,Schotte C, Lukat P, Deuschmann A, Blankenfeldt W, Cox RJ Angew Chem Int Ed Engl. 2021 Jun 28. doi: 10.1002/anie.202106718. PMID:34180566[4]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Bailey AM, Cox RJ, Harley K, Lazarus CM, Simpson TJ, Skellam E. Characterisation of 3-methylorcinaldehyde synthase (MOS) in Acremonium strictum: first observation of a reductive release mechanism during polyketide biosynthesis. Chem Commun (Camb). 2007 Oct 21;(39):4053-5. doi: 10.1039/b708614h. Epub 2007 Jul, 25. PMID:17912413 doi:http://dx.doi.org/10.1039/b708614h
- ↑ Fisch KM, Skellam E, Ivison D, Cox RJ, Bailey AM, Lazarus CM, Simpson TJ. Catalytic role of the C-terminal domains of a fungal non-reducing polyketide synthase. Chem Commun (Camb). 2010 Aug 7;46(29):5331-3. doi: 10.1039/c0cc01162b. Epub 2010 , Jun 16. PMID:20552126 doi:http://dx.doi.org/10.1039/c0cc01162b
- ↑ Schor R, Schotte C, Wibberg D, Kalinowski J, Cox RJ. Three previously unrecognised classes of biosynthetic enzymes revealed during the production of xenovulene A. Nat Commun. 2018 May 17;9(1):1963. doi: 10.1038/s41467-018-04364-9. PMID:29773797 doi:http://dx.doi.org/10.1038/s41467-018-04364-9
- ↑ Schotte C, Lukat P, Deuschmann A, Blankenfeldt W, Cox RJ. Understanding and Engineering the Stereoselectivity of Humulene Synthase. Angew Chem Int Ed Engl. 2021 Jun 28. doi: 10.1002/anie.202106718. PMID:34180566 doi:http://dx.doi.org/10.1002/anie.202106718
