Structural highlights
Function
[ARIS_ASPTE] Catalyzes the cyclization of trans,trans-farnesyl diphosphate (FPP) to the bicyclic sesquiterpene aristolochene. Produces germacrene A as an enzyme-bound intermediate that is not released by the enzyme, but is further cyclized to produce aristolochene. Aristolochene is the likely parent compound for a number of sesquiterpenoid toxins produced by filamentous fungi.[1] [2]
Publication Abstract from PubMed
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 pi 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.
Mechanistic insights from the binding of substrate and carbocation intermediate analogues to aristolochene synthase.,Chen M, Al-Lami N, Janvier M, D'Antonio EL, Faraldos JA, Cane DE, Allemann RK, Christianson DW Biochemistry. 2013 Aug 13;52(32):5441-53. doi: 10.1021/bi400691v. Epub 2013 Aug, 1. PMID:23905850[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Cane DE, Kang I. Aristolochene synthase: purification, molecular cloning, high-level expression in Escherichia coli, and characterization of the Aspergillus terreus cyclase. Arch Biochem Biophys. 2000 Apr 15;376(2):354-64. PMID:10775423 doi:10.1006/abbi.2000.1734
- ↑ Felicetti B, Cane DE. Aristolochene synthase: mechanistic analysis of active site residues by site-directed mutagenesis. J Am Chem Soc. 2004 Jun 16;126(23):7212-21. PMID:15186158 doi:10.1021/ja0499593
- ↑ 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 Aug 13;52(32):5441-53. doi: 10.1021/bi400691v. Epub 2013 Aug, 1. PMID:23905850 doi:10.1021/bi400691v
