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. 2022 Feb 7;61(7):e202113189.
doi: 10.1002/anie.202113189. Epub 2021 Dec 27.

Identification of Cyclopropane Formation in the Biosyntheses of Hormaomycins and Belactosins: Sequential Nitration and Cyclopropanation by Metalloenzymes

Xiaojun Li  1 , Ryo Shimaya  2 , Tohru Dairi  3 , Wei-Chen Chang  1 , Yasushi Ogasawara  3
Affiliations

Identification of Cyclopropane Formation in the Biosyntheses of Hormaomycins and Belactosins: Sequential Nitration and Cyclopropanation by Metalloenzymes

Xiaojun Li et al. Angew Chem Int Ed Engl. .

Abstract

Hormaomycins and belactosins are peptide natural products that contain unusual cyclopropane moieties. Bioinformatics analysis of the corresponding biosynthetic gene clusters showed that two conserved genes, hrmI/belK and hrmJ/belL, were potential candidates for catalyzing cyclopropanation. Using in vivo and in vitro assays, the functions of HrmI/BelK and HrmJ/BelL were established. HrmI and BelK, which are heme oxygenase-like dinuclear iron enzymes, catalyze oxidation of the ϵ-amino group of l-lysine to afford l-6-nitronorleucine. Subsequently, HrmJ and BelL, which are iron- and α-ketoglutarate-dependent oxygenases, effectively convert l-6-nitronorleucine into 3-(trans-2-nitrocyclopropyl)-alanine through C4-C6 bond installation. These observations disclose a novel pathway of cyclopropane ring construction and exemplify the new chemistry involving metalloenzymes in natural product biosynthesis.

Keywords: Biosynthesis; Cyclopropane; Metalloenzymes; Natural products; Peptides.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1.
Figure 1.
Structure of hormaomycins and belactosin A (left) and biosynthetic pathway of 3 identified in this study (right). Hormaomycins and belactosin A contain uncommon 3-(trans-2-nitrocyclopropyl)-alanine and 3-(trans-2-aminocyclopropyl)-alanine moieties, respectively (highlighted in blue).
Figure 2.
Figure 2.
LC-MS chromatograms of i) HrmI reaction without 1, ii) incubation of 1 without enzyme, iii) HrmI reaction with 1, iv) BelK reaction with 1, v) HrmI+HrmJ reaction with 1, vi) HrmJ reaction without α-KG, vii) incubation of 2 without enzyme, viii) HrmJ reaction without 2, ix) HrmJ reaction with 2, and x) BelL reaction with 2. Chromatograms were monitored with m/z 147.1 (black traces for 1), 177.1 (blue traces for 2), and 175.1 (red traces for 3).
Figure 3.
Figure 3.
(a) 13C-NMR spectra of HrmI, HrmJ, BelK, and BelL-catalyzed reactions using 6-13C-1 or 6-13C-2 as substrate. (b) 13C-NMR spectra of 6-13C-2 under different pH conditions. Insets (highlighted in blue) are 13C-NMR spectra recorded in C–H coupling mode.
Scheme 1.
Scheme 1.
Proposed reaction mechanism for HrmJ and BelL-catalyzed reactions.
See this image and copyright information in PMC

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