Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 113, Issue 14, Pages 3797-3802Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1519695113
Keywords
natural products; biosynthesis; halogenation; enzymology
Categories
Funding
- US National Science Foundation [OCE-1313747]
- US National Institutes of Health (NIH) [P01-ES021921, R01-AI47818, R21-AI119311]
- Mote Protect Our Reef Grant Program [POR-2012-3]
- Dart Foundation
- Smithsonian Competitive Grants Program for Science
- Howard Hughes Medical Institute
- NIH Marine Biotechnology Training Grant Predoctoral Fellowship [T32-GM067550]
- Helen Hay Whitney Foundation Postdoctoral Fellowship
- Swiss National Science Foundation Postdoctoral Fellowship
- Directorate For Geosciences
- Division Of Ocean Sciences [1313747] Funding Source: National Science Foundation
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Halogenated pyrroles (halopyrroles) are common chemical moieties found in bioactive bacterial natural products. The halopyrrole moieties of mono-and dihalopyrrole-containing compounds arise from a conserved mechanism in which a proline-derived pyrrolyl group bound to a carrier protein is first halogenated and then elaborated by peptidic or polyketide extensions. This paradigm is broken during the marine pseudoalteromonad bacterial biosynthesis of the coral larval settlement cue tetrabromopyrrole (1), which arises from the substitution of the proline-derived carboxylate by a bromine atom. To understand the molecular basis for decarboxylative bromination in the biosynthesis of 1, we sequenced two Pseudoalteromonas genomes and identified a conserved four-gene locus encoding the enzymes involved in its complete biosynthesis. Through total in vitro reconstitution of the biosynthesis of 1 using purified enzymes and biochemical interrogation of individual biochemical steps, we show that all four bromine atoms in 1 are installed by the action of a single flavin-dependent halogenase: Bmp2. Tetrabromination of the pyrrole induces a thioesterase-mediated offloading reaction from the carrier protein and activates the biosynthetic intermediate for decarboxylation. Insights into the tetrabrominating activity of Bmp2 were obtained from the high-resolution crystal structure of the halogenase contrasted against structurally homologous halogenase Mpy16 that forms only a dihalogenated pyrrole in marinopyrrole biosynthesis. Structure-guided mutagenesis of the proposed substrate- binding pocket of Bmp2 led to a reduction in the degree of halogenation catalyzed. Our study provides a biogenetic basis for the biosynthesis of 1 and sets a firm foundation for querying the biosynthetic potential for the production of 1 in marine (meta) genomes.
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