Tryptophan 7-halogenase (PrnA) structure suggests a mechanism for regioselective chlorination

Science. 2005 Sep 30;309(5744):2216-9. doi: 10.1126/science.1116510.

Abstract

Chlorinated natural products include vancomycin and cryptophycin A. Their biosynthesis involves regioselective chlorination by flavin-dependent halogenases. We report the structural characterization of tryptophan 7-halogenase (PrnA), which regioselectively chlorinates tryptophan. Tryptophan and flavin adenine dinucleotide (FAD) are separated by a 10 angstrom-long tunnel and bound by distinct enzyme modules. The FAD module is conserved in halogenases and is related to flavin-dependent monooxygenases. On the basis of biochemical studies, crystal structures, and by analogy with monooxygenases, we predict that FADH2 reacts with O2 to make peroxyflavin, which is decomposed by Cl-. The resulting HOCl is guided through the tunnel to tryptophan, where it is activated to participate in electrophilic aromatic substitution.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Binding Sites
  • Chlorides / metabolism*
  • Crystallography, X-Ray
  • Dimerization
  • Flavin-Adenine Dinucleotide / analogs & derivatives
  • Flavin-Adenine Dinucleotide / metabolism
  • Hydrogen Bonding
  • Hypochlorous Acid / metabolism
  • Indoles / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Oxidation-Reduction
  • Oxidoreductases / chemistry*
  • Oxidoreductases / isolation & purification
  • Oxidoreductases / metabolism
  • Oxygen / metabolism
  • Protein Conformation
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Pseudomonas fluorescens / enzymology*
  • Tryptophan / analogs & derivatives
  • Tryptophan / metabolism

Substances

  • Chlorides
  • Indoles
  • Flavin-Adenine Dinucleotide
  • 7-chlorotryptophan
  • 1,5-dihydro-FAD
  • Hypochlorous Acid
  • Tryptophan
  • Oxidoreductases
  • tryptophan halogenase
  • 5-methylindole
  • Oxygen

Associated data

  • PDB/2APG
  • PDB/2AQJ
  • PDB/2AR8
  • PDB/2ARD