title: Tryptophan 7-halogenase (PrnA) structure suggests a mechanism for regioselective chlorination.
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.
authors.affiliation: Centre for Biomolecular Sciences, EaStchem, University of St. Andrews, St. Andrews KY16 9ST, UK.
authors.forename: Changjiang
authors.initials: C
authors.lastname: Dong
authors.forename: Silvana
authors.initials: S
authors.lastname: Flecks
authors.forename: Susanne
authors.initials: S
authors.lastname: Unversucht
authors.forename: Caroline
authors.initials: C
authors.lastname: Haupt
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: van Pée
authors.forename: James H
authors.initials: JH
authors.lastname: Naismith
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002712:Chlorides / Q000378:metabolism*; D018360:Crystallography, X-Ray; D019281:Dimerization; D005182:Flavin-Adenine Dinucleotide / Q000031:analogs & derivatives / Q000378:metabolism; D006860:Hydrogen Bonding; D006997:Hypochlorous Acid / Q000378:metabolism; D007211:Indoles / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011551:Pseudomonas fluorescens / Q000201:enzymology*; D014364:Tryptophan / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D002712:Chlorides; D007211:Indoles; D005182:Flavin-Adenine Dinucleotide; C037586:7-chlorotryptophan; C058805:1,5-dihydro-FAD; D006997:Hypochlorous Acid; D014364:Tryptophan; D010088:Oxidoreductases; C407363:tryptophan halogenase; C093726:5-methylindole; D010100:Oxygen