# Discovery and Functional Characterization of SnFDHal, an Efficient Tryptophan 5-Halogenase from Streptomyces noursei

## TL;DR

Scientists discovered a new enzyme from a soil bacterium that efficiently adds chlorine to a key amino acid, which could help in making better drugs and agrochemicals.

## Contribution

The discovery and characterization of SnFDHal, a novel and efficient tryptophan 5-halogenase from Streptomyces noursei.

## Key findings

- SnFDHal shows high catalytic efficiency for chlorinating L-tryptophan compared to other FDHs.
- The enzyme is thermostable with a melting temperature of 46.7°C at pH 6 and 8.
- Structural modeling suggests a conserved phenylalanine residue promotes halogenation at the C-5 position of L-tryptophan.

## Abstract

Flavin-dependent halogenases (FDHs) are a class of enzymes renowned for their regioselective ability to precisely insert halogen atoms into small aromatic compounds. Halogen incorporation can enhance the physicochemical and biological properties of molecules, making them valuable for agrochemical and pharmaceutical applications. Through bioinformatic mining of bacterial genomes, we discovered and functionally characterized SnFDHal, an efficient tryptophan 5-halogenase from Streptomyces noursei NRRL B-1714. This halogenase operates across a broad pH range and exhibits a melting temperature of 46.7 °C at both pH 6 and pH 8, which is comparable to thermophilic halogenases such as Th-Hal and BorH, and notably higher than those of mesophilic counterparts. Steady-state kinetic analysis revealed that SnFDHal displays superior catalytic efficiency for the chlorination of L-tryptophan compared to other FDHs reported to date. Structural modeling of its active site suggests that a conserved bulky phenylalanine residue (F49) promotes halogenation at the C-5 position of L-tryptophan, consistent with experimental findings. The combination of high catalytic efficiency and thermostability positions SnFDHal as a promising biocatalyst for applications in agrochemical and pharmaceutical industries.

The online version contains supplementary material available at 10.1007/s12010-025-05449-0.