Cysteine Dealkylation in by a Novel Flavin-Dependent Monooxygenase.

In this paper, we describe the biochemical reconstitution of a cysteine salvage pathway and the biochemical characterization of each of the five enzymes involved. The salvage begins with amine acetylation of -alkylcysteine, followed by thioether oxidation. The C-S bond of the resulting sulfoxide is cleaved using a new flavoenzyme catalytic motif to give -acetylcysteine sulfenic acid.

Mechanistic Studies on the Radical SAM Enzyme Tryptophan Lyase (NosL).

Tryptophan lyase (NosL) is a radical SAM enzyme that catalyzes the formation of 3-methyl-2-indolic acid from l-tryptophan in the biosynthesis of the antibiotic nosiheptide. NosL is the newest addition to the radical SAM-dependent aromatic amino acid lyase subfamily which includes ThiH, HydG, and CofH. The recently solved crystal structure of NosL challenged the previously accepted mechanistic hypothesis and spurred a renewed interest in investigating the reaction.

Mechanistic Studies on Tryptophan Lyase (NosL): Identification of Cyanide as a Reaction Product.

Tryptophan lyase (NosL) catalyzes the formation of 3-methylindole-2-carboxylic acid and 3-methylindole from l-tryptophan. In this paper, we provide evidence supporting a formate radical intermediate and demonstrate that cyanide is a byproduct of the NosL-catalyzed reaction with l-tryptophan. These experiments require a major revision of the NosL mechanism and uncover an unanticipated connection between NosL and HydG, the radical SAM enzyme that forms cyanide and carbon monoxide from tyrosine during the biosynthesis of the metallo-cluster of the [Fe-Fe] hydrogenase.

Tryptophan Lyase (NosL): A Cornucopia of 5'-Deoxyadenosyl Radical Mediated Transformations.

Tryptophan lyase (NosL) is a radical S-adenosyl-l-methionine (SAM) enzyme that catalyzes the formation of 3-methyl-2-indolic acid from l-tryptophan. In this paper, we demonstrate that the 5'-deoxyadenosyl radical is considerably more versatile in its chemistry than previously anticipated: hydrogen atom abstraction from N-cyclopropyltryptophan occurs at Cα rather than the amino group with NosL Y90A and replacing the substrate amine with a ketone or an alkene changes the chemistry from hydrogen atom abstraction to double bond addition. In addition, the 5'-deoxyadenosyl radical can add to the [4Fe-4S] cluster and dithionite can be used to trap radicals at the active site.

Identification of the First Riboflavin Catabolic Gene Cluster Isolated from Microbacterium maritypicum G10.

Riboflavin is a common cofactor, and its biosynthetic pathway is well characterized. However, its catabolic pathway, despite intriguing hints in a few distinct organisms, has never been established. This article describes the isolation of a Microbacterium maritypicum riboflavin catabolic strain, and the cloning of the riboflavin catabolic genes.

Tryptophan Lyase (NosL): Mechanistic Insights from Substrate Analogues and Mutagenesis.

NosL is a member of a family of radical S-adenosylmethionine enzymes that catalyze the cleavage of the Cα-Cβ bond of aromatic amino acids. In this paper, we describe a set of experiments with substrate analogues and mutants for probing the early steps of the NosL mechanism. We provide biochemical evidence in support of the structural studies showing that the 5'-deoxyadenosyl radical abstracts a hydrogen atom from the amino group of tryptophan.