6UL2

Crystal structure of tryptophan-6-halogenase BorH complexed with L-tryptophan

Summary for 6UL2

• Entry DOI: 10.2210/pdb6ul2/pdb
• Descriptor: Tryptophan 6-halogenase, TRYPTOPHAN, SULFATE ION, ... (4 entities in total)
• Functional Keywords: halogenase oxidoreductase, flavoprotein
• Biological source: uncultured bacterium
• Total number of polymer chains: 4
• Total formula weight: 244218.93

Authors

Lingkon, K.,Bellizzi, J.J. (deposition date: 2019-10-06, release date: 2019-12-25, Last modification date: 2023-10-11)

Primary citation

Lingkon, K.,Bellizzi 3rd, J.J.
Structure and Activity of the Thermophilic Tryptophan-6 Halogenase BorH.
Chembiochem, 21:1121-1128, 2020

PubMed Abstract: Flavin-dependent halogenases carry out regioselective aryl halide synthesis in aqueous solution at ambient temperature and neutral pH using benign halide salts, making them attractive catalysts for green chemistry. BorH and BorF, two proteins encoded by the biosynthetic gene cluster for the chlorinated bisindole alkaloid borregomycin A, are the halogenase and flavin reductase subunits of a tryptophan-6-halogenase. Quantitative conversion of l-tryptophan (Trp) to 6-chlorotryptophan could be achieved using 1.2 mol % BorH and 2 mol % BorF. The optimal reaction temperature for Trp chlorination is 45 °C, and the melting temperatures of BorH and BorF are 48 and 50 °C respectively, which are higher than the thermal parameters for most other halogenases previously studied. Steady-state kinetic analysis of Trp chlorination by BorH determined parameters of k =4.42 min , and K of 9.78 μm at 45 °C. BorH exhibits a broad substrate scope, chlorinating and brominating a variety of aromatic substrates with and without indole groups. Chlorination of Trp at a 100 mg scale with 52 % crude yield, using 0.2 mol % BorH indicates that industrial scale biotransformations using BorH/BorF are feasible. The X-ray crystal structure of BorH with bound Trp provides additional evidence for the model that regioselectivity is determined by substrate positioning in the active site, showing C6 of Trp juxtaposed with the catalytic Lys79 in the same binding pose previously observed in the structure of Thal.

PubMed: 31692209
DOI: 10.1002/cbic.201900667

Experimental method

X-RAY DIFFRACTION (1.979 Å)