| 1. |
- Auman, Dirk, et al.
(författare)
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Peroxy Intermediate Drives Carbon Bond Activation in the Dioxygenase AsqJ
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:34, s. 15622-15632
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Tidskriftsartikel (refereegranskat)abstract
- Dioxygenases catalyze stereoselective oxygen atom transfer in metabolic pathways of biological, industrial, and pharmaceutical importance, but their precise chemical principles remain controversial. The α-ketoglutarate (αKG)-dependent dioxygenase AsqJ synthesizes biomedically active quinolone alkaloids via desaturation and subsequent epoxidation of a carbon–carbon bond in the cyclopeptin substrate. Here, we combine high-resolution X-ray crystallography with enzyme engineering, quantum-classical (QM/MM) simulations, and biochemical assays to describe a peroxidic intermediate that bridges the substrate and active site metal ion in AsqJ. Homolytic cleavage of this moiety during substrate epoxidation generates an activated high-valent ferryl (FeIV = O) species that mediates the next catalytic cycle, possibly without the consumption of the metabolically valuable αKG cosubstrate. Our combined findings provide an important understanding of chemical bond activation principles in complex enzymatic reaction networks and molecular mechanisms of dioxygenases.
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| 2. |
- Bräuer, Alois, et al.
(författare)
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Structural snapshots of the minimal PKS system responsible for octaketide biosynthesis
- 2020
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Ingår i: Nature Chemistry. - : Springer Science and Business Media LLC. - 1755-4330 .- 1755-4349. ; 12:8
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Tidskriftsartikel (refereegranskat)abstract
- The invariable core of a type II polyketide synthase has been characterized using X-ray crystallography, simulations, mutagenesis experiments and functional assays. The characterization of the ternary acyl carrier protein complexes provides a mechanistic understanding of the reactivity and could inform future engineering of this complex biosynthetic machinery. Type II polyketide synthases (PKSs) are multi-enzyme complexes that produce secondary metabolites of medical relevance. Chemical backbones of such polyketides are produced by minimal PKS systems that consist of a malonyl transacylase, an acyl carrier protein and an alpha/beta heterodimeric ketosynthase. Here, we present X-ray structures of all ternary complexes that constitute the minimal PKS system for anthraquinone biosynthesis inPhotorhabdus luminescens. In addition, we characterize this invariable core using molecular simulations, mutagenesis experiments and functional assays. We show that malonylation of the acyl carrier protein is accompanied by major structural rearrangements in the transacylase. Principles of an ongoing chain elongation are derived from the ternary complex with a hexaketide covalently linking the heterodimeric ketosynthase with the acyl carrier protein. Our results for the minimal PKS system provide mechanistic understanding of PKSs and a fundamental basis for engineering PKS pathways for future applications.
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