9H6Z

AetF, a single-component flavin-dependent tryptophan halogenase, in complex with tryptoline

Summary for 9H6Z

• Entry DOI: 10.2210/pdb9h6z/pdb
• Related: 8CJD 8CJE 8CJF 8CJG
• Descriptor: AetF, FLAVIN-ADENINE DINUCLEOTIDE, 2,3,4,9-tetrahydro-1~{H}-pyrido[3,4-b]indole, ... (6 entities in total)
• Functional Keywords: single-component halogenase, tryptophan halogenase, non-native substrate, unnatural substrate, flavoprotein
• Biological source: Aetokthonos hydrillicola Thurmond2011
• Total number of polymer chains: 2
• Total formula weight: 156705.15

Authors

Bork, S.,Niemann, H.H. (deposition date: 2024-10-25, release date: 2026-05-06, Last modification date: 2026-07-08)

Primary citation

Bork, S.,Horstmeier, H.J.,Scharkowski, B.,Niemann, H.H.
Structural basis of regioselective double halogenation of the beta-carboline tryptoline by the single-component halogenase AetF.
Acta Crystallogr D Struct Biol, 82:836-844, 2026

PubMed Abstract: Flavin-dependent halogenases (FDHs) offer a biocatalytic route to regioselective halogenation of aromatic substrates under mild conditions. AetF, a rare self-sufficient single-component FDH, catalyzes sequential dibromination of tryptophan and has a broad substrate scope. Here, we report the crystal structure of AetF in complex with the non-native substrate tryptoline, a tricyclic β-carboline with pharmacological relevance. The structure reveals that tryptoline binds in a pose analogous to the natural AetF substrate L-tryptophan, positioning its C6 atom for initial halogenation. Enzymatic assays confirmed AetF-mediated monobromination and dibromination of tryptoline, yielding 6,8-dibromotryptoline as the final product. In accordance with the observed binding pose of the substrate tryptoline, the monobrominated initial product was almost exclusively 6-bromotryptoline. A crystal structure of AetF in complex with the minor monobrominated product 8-bromotryptoline provides insight into the effect of bromine substituents in different positions on the binding affinity and into potential pathways to the formation of 6,8-dibromotryptoline. These findings define the structural basis of site-selective halogenation of a non-native substrate by AetF and provide structural guidance for enzyme engineering.

PubMed: 42329691
DOI: 10.1107/S2059798326005954

Experimental method

X-RAY DIFFRACTION (1.87 Å)