Single-Enzyme Conversion of Tryptophan to Skatole and Cyanide Expands the Mechanistic Competence of Diiron Oxidases.

Skatole is a pungent heterocyclic compound derived from the essential amino acid l-tryptophan by bacteria in the mammalian digestive tract. The four-step anaerobic conversion of tryptophan to skatole is well-established; though, to date, no aerobic counterpart has been reported. Herein, we report the discovery of the oxygen-dependent skatole synthase SktA that single-handedly converts 5-bromo-l-tryptophan to 5-bromoskatole, obviating the need for a multienzyme process.

A single diiron enzyme catalyses the oxidative rearrangement of tryptophan to indole nitrile.

Nitriles are uncommon in nature and are typically constructed from oximes through the oxidative decarboxylation of amino acid substrates or from the derivatization of carboxylic acids. Here we report a third nitrile biosynthesis strategy featuring the cyanobacterial nitrile synthase AetD. During the biosynthesis of the eagle-killing neurotoxin, aetokthonotoxin, AetD transforms the 2-aminopropionate portion of 5,7-dibromo-L-tryptophan to a nitrile.

Linking bacterial tetrabromopyrrole biosynthesis to coral metamorphosis.

An important factor dictating coral fitness is the quality of bacteria associated with corals and coral reefs. One way that bacteria benefit corals is by stimulating the larval to juvenile life cycle transition of settlement and metamorphosis. Tetrabromopyrrole (TBP) is a small molecule produced by bacteria that stimulates metamorphosis with and without attachment in a range of coral species.

Oxidative rearrangement of tryptophan to indole nitrile by a single diiron enzyme.

Nitriles are uncommon in nature and are typically constructed from oximes via the oxidative decarboxylation of amino acid substrates or from the derivatization of carboxylic acids. Here we report a third strategy of nitrile biosynthesis featuring the cyanobacterial nitrile synthase AetD. During the biosynthesis of the 'eagle-killing' neurotoxin, aetokthonotoxin, AetD converts the alanyl side chain of 5,7-dibromo-L-tryptophan to a nitrile.

Linking bacterial tetrabromopyrrole biosynthesis to coral metamorphosis.

An important factor dictating coral fitness is the quality of bacteria associated with corals and coral reefs. One way that bacteria benefit corals is by stimulating the larval to juvenile life cycle transition of settlement and metamorphosis. Tetrabromopyrrole (TBP) is a small molecule produced by bacteria that stimulates metamorphosis in a range of coral species.

Structural Basis of Stereospecific Vanadium-Dependent Haloperoxidase Family Enzymes in Napyradiomycin Biosynthesis.

Vanadium-dependent haloperoxidases (VHPOs) from bacteria differ from their counterparts in fungi, macroalgae, and other bacteria by catalyzing organohalogenating reactions with strict regiochemical and stereochemical control. While this group of enzymes collectively uses hydrogen peroxide to oxidize halides for incorporation into electron-rich organic molecules, the mechanism for the controlled transfer of highly reactive chloronium ions in the biosynthesis of napyradiomycin and merochlorin antibiotics sets the vanadium-dependent chloroperoxidases apart. Here we report high-resolution crystal structures of two homologous VHPO family members associated with napyradiomycin biosynthesis, NapH1 and NapH3, that catalyze distinctive chemical reactions in the construction of meroterpenoid natural products.

From Tryptophan to Toxin: Nature's Convergent Biosynthetic Strategy to Aetokthonotoxin.

Aetokthonotoxin (AETX) is a cyanobacterial neurotoxin that causes vacuolar myelinopathy, a neurological disease that is particularly deadly to bald eagles in the United States. The recently characterized AETX is structurally unique among cyanotoxins and is composed of a pentabrominated biindole nitrile. Herein we report the discovery of an efficient, five-enzyme biosynthetic pathway that the freshwater cyanobacterium uses to convert two molecules of tryptophan to AETX.

Cryptic halogenation reactions in natural product biosynthesis.

Covering: Up to December 2020Enzymatic halogenation reactions are essential for the production of thousands of halogenated natural products. However, in recent years, scientists discovered several halogenases that transiently incorporate halogen atoms in intermediate biosynthetic molecules to activate them for further chemical reactions such as cyclopropanation, terminal alkyne formation, C-/O-alkylation, biaryl coupling, and C-C rearrangements. In each case, the halogen atom is lost in the course of biosynthesis to the final product and is hence termed "cryptic".

Flavin-N5-oxide intermediates in dibenzothiophene, uracil, and hexachlorobenzene catabolism.

Flavin-N5-oxide is a new intermediate in flavoenzymology. Here we describe the identification of DszA (dibenzothiophene catabolism), RutA (uracil catabolism) and HcbA1 (hexachlorobenzene catabolism) as flavin-N5-oxide-utilizing enzymes. Mechanistic analysis of these reactions suggests a model for the identification of other examples of this catalytic motif.

Hexachlorobenzene Catabolism Involves a Nucleophilic Aromatic Substitution and Flavin-N5-Oxide Formation.

HcbA1 is a unique flavoenzyme that catalyzes the first step in the bacterial hexachlorobenzene catabolic pathway. Here we report in vitro reconstitution of the HcbA1-catalyzed reaction. Detailed mechanistic studies provide evidence for nucleophilic aromatic substitution and flavin-N5-oxide formation.

Flavin-N5-oxide: A new, catalytic motif in flavoenzymology.

Flavin-N5-oxide is a recently discovered intermediate used by EncM (1,3-diketone oxidation), DszA (sulfone monooxygenase) and RutA (amide monooxygenase). This review describes the mechanism of these enzymes and proposes criteria for the identification of additional Flavin-N5-oxide dependent enzymes.

RutA-Catalyzed Oxidative Cleavage of the Uracil Amide Involves Formation of a Flavin-N5-oxide.

RutA is a novel flavoenzyme on the uracil catabolic pathway that catalyzes uracil ring opening by a unique amide oxidation reaction. Here we provide evidence that this reaction also involves the formation of a flavin-N5-oxide.

Dibenzothiophene Catabolism Proceeds via a Flavin-N5-oxide Intermediate.

The dibenzothiophene catabolic pathway converts dibenzothiophene to 2-hydroxybiphenyl and sulfite. The third step of the pathway, involving the conversion of dibenzothiophene sulfone to 2-(2-hydroxyphenyl)-benzenesulfinic acid, is catalyzed by a unique flavoenzyme DszA. Mechanistic studies on this reaction suggest that the C2 hydroperoxide of dibenzothiophene sulfone reacts with flavin to form a flavin-N5-oxide.