title: Tandem action of the O2- and FADH2-dependent halogenases KtzQ and KtzR produce 6,7-dichlorotryptophan for kutzneride assembly.
abstract: Kutznerides are actinomycete-derived antifungal nonribosomal hexadepsipeptides which are assembled from five unsual nonproteinogenic amino acids and one hydroxy acid. Conserved in all structurally characterized kutznerides is a dichlorinated tricyclic hexahydropyrroloindole postulated to be derived from 6,7-dichlorotryptophan. In this Communication, we identify KtzQ and KtzR as tandem acting FADH2-dependent halogenases that work sequentially on free L-tryptophan to generate 6,7-dichloro-L-tryptophan. Kinetic characterization of these two enzymes has shown that KtzQ (along with the flavin reductase KtzS) acts first to chlorinate at the 7-position of L-tryptophan. KtzR, with a 120 fold preference for 7-chloro-L-tryptophan over L-tryptophan, then installs the second chlorine at the 6-position of 7-chloro-L-tryptophan to generate 6,7-dichloro-L-tryptophan. These findings provide further insights into the enzymatic logic of carbon-chloride bond formation during the biosynthesis of halogenated secondary metabolites.
authors.affiliation: Department of Biological Chemistry & Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: John R
authors.initials: JR
authors.lastname: Heemstra
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Walsh
mesh_terms: D039903:Actinobacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003500:Cyclization; D047630:Depsipeptides / Q000096:biosynthesis* / Q000737:chemistry; D005182:Flavin-Adenine Dinucleotide / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D054879:Halogenation; D008968:Molecular Conformation; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D013237:Stereoisomerism; D013997:Time Factors; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000737:chemistry
chemical_list: C533763:6,7-dichlorotryptophan; D001426:Bacterial Proteins; D002712:Chlorides; D047630:Depsipeptides; D009097:Multienzyme Complexes; D005182:Flavin-Adenine Dinucleotide; C058805:1,5-dihydro-FAD; D014364:Tryptophan; D010088:Oxidoreductases; D010100:Oxygen