AetF, a single-component flavin-dependent tryptophan halogenase, in complex with 7-bromo-L-tryptophan

Experimental Data Snapshot

  • Resolution: 2.30 Å
  • R-Value Free: 0.190 
  • R-Value Work: 0.153 
  • R-Value Observed: 0.155 

Starting Model: experimental
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Structural basis of regioselective tryptophan dibromination by the single-component flavin-dependent halogenase AetF.

Gafe, S.Niemann, H.H.

(2023) Acta Crystallogr D Struct Biol 79: 596-609

  • DOI: https://doi.org/10.1107/S2059798323004254
  • Primary Citation of Related Structures:  
    8CJD, 8CJE, 8CJF, 8CJG

  • PubMed Abstract: 

    The flavin-dependent halogenase (FDH) AetF successively brominates tryptophan at C5 and C7 to generate 5,7-dibromotryptophan. In contrast to the well studied two-component tryptophan halogenases, AetF is a single-component flavoprotein monooxygenase. Here, crystal structures of AetF alone and in complex with various substrates are presented, representing the first experimental structures of a single-component FDH. Rotational pseudosymmetry and pseudomerohedral twinning complicated the phasing of one structure. AetF is structurally related to flavin-dependent monooxygenases. It contains two dinucleotide-binding domains for binding the ADP moiety with unusual sequences that deviate from the consensus sequences GXGXXG and GXGXXA. A large domain tightly binds the cofactor flavin adenine dinucleotide (FAD), while the small domain responsible for binding the nicotinamide adenine dinucleotide (NADP) is unoccupied. About half of the protein forms additional structural elements containing the tryptophan binding site. FAD and tryptophan are about 16 Å apart. A tunnel between them presumably allows diffusion of the active halogenating agent hypohalous acid from FAD to the substrate. Tryptophan and 5-bromotryptophan bind to the same site but with a different binding pose. A flip of the indole moiety identically positions C5 of tryptophan and C7 of 5-bromotryptophan next to the tunnel and to catalytic residues, providing a simple explanation for the regioselectivity of the two successive halogenations. AetF can also bind 7-bromotryptophan in the same orientation as tryptophan. This opens the way for the biocatalytic production of differentially dihalogenated tryptophan derivatives. The structural conservation of a catalytic lysine suggests a way to identify novel single-component FDHs.

  • Organizational Affiliation

    Department of Chemistry, Bielefeld University, Universitaetsstrasse 25, 33615 Bielefeld, Germany.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
663Aetokthonos hydrillicola Thurmond2011Mutation(s): 0 
Gene Names: aetF
Find proteins for A0A861B9Z9 (Aetokthonos hydrillicola Thurmond2011)
Explore A0A861B9Z9 
Go to UniProtKB:  A0A861B9Z9
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupA0A861B9Z9
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 5 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
FAD (Subject of Investigation/LOI)
Query on FAD

Download Ideal Coordinates CCD File 
C [auth A],
K [auth B]
C27 H33 N9 O15 P2
UV3 (Subject of Investigation/LOI)
Query on UV3

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D [auth A],
L [auth B]
C11 H11 Br N2 O2
Query on PGE

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I [auth A],
P [auth B]
C6 H14 O4
Query on PEG

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M [auth B],
O [auth B]
C4 H10 O3
Query on EDO

Download Ideal Coordinates CCD File 
E [auth A]
F [auth A]
G [auth A]
H [auth A]
J [auth A]
E [auth A],
F [auth A],
G [auth A],
H [auth A],
J [auth A],
N [auth B]
C2 H6 O2
Experimental Data & Validation

Experimental Data

Unit Cell:
Length ( Å )Angle ( ˚ )
a = 122.326α = 90
b = 122.326β = 90
c = 87.163γ = 90
Software Package:
Software NamePurpose
MxCuBEdata collection
XDSdata reduction
XDSdata scaling
Cootmodel building

Structure Validation

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Ligand Structure Quality Assessment 

Entry History & Funding Information

Deposition Data

Funding OrganizationLocationGrant Number
Not fundedGermany--

Revision History  (Full details and data files)

  • Version 1.0: 2023-06-14
    Type: Initial release
  • Version 1.1: 2023-06-28
    Changes: Database references
  • Version 1.2: 2023-07-12
    Changes: Database references
  • Version 1.3: 2024-06-19
    Changes: Data collection, Refinement description