title: Two interconverting Fe(IV) intermediates in aliphatic chlorination by the halogenase CytC3.
abstract: Enzymatic incorporation of a halogen atom is a common feature in the biosyntheses of more than 4,500 natural products. Halogenation of unactivated carbon centers in the biosyntheses of several compounds of nonribosomal peptide origin is carried out by a class of mononuclear nonheme iron enzymes that require alpha-ketoglutarate (alphaKG, 1), chloride and oxygen. To investigate the ability of these enzymes to functionalize unactivated methyl groups, we characterized the chlorination of the gamma-methyl substituent of L-2-aminobutyric acid (L-Aba, 2) attached to the carrier protein CytC2 by iron halogenase (CytC3) from soil Streptomyces sp. We identified an intermediate state comprising two high-spin Fe(IV) complexes in rapid equilibrium. At least one of the Fe(IV) complexes abstracts hydrogen from the substrate. The demonstration that chlorination proceeds through an Fe(IV) intermediate that cleaves a C-H bond reveals the mechanistic similarity of aliphatic halogenases to the iron- and alphaKG-dependent hydroxylases.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Ave., Boston, Massachusetts 02115, USA.
authors.forename: Danica P
authors.initials: DP
authors.lastname: Galonić
authors.forename: Eric W
authors.initials: EW
authors.lastname: Barr
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Walsh
authors.forename: J Martin
authors.initials: JM
authors.lastname: Bollinger
authors.forename: Carsten
authors.initials: C
authors.lastname: Krebs
mesh_terms: D000613:Aminobutyrates / Q000737:chemistry; D002352:Carrier Proteins / Q000737:chemistry; D020134:Catalytic Domain; D002713:Chlorine / Q000737:chemistry*; D003903:Deuterium / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D007656:Ketoglutaric Acids / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D019159:Nonheme Iron Proteins / Q000737:chemistry*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D015204:Spectroscopy, Mossbauer; D013302:Streptomyces / Q000201:enzymology
chemical_list: D000613:Aminobutyrates; D002352:Carrier Proteins; D007656:Ketoglutaric Acids; D019159:Nonheme Iron Proteins; C066317:ferryl iron; D002713:Chlorine; C012223:alpha-aminobutyric acid; D003903:Deuterium; D007501:Iron; D010088:Oxidoreductases; D010100:Oxygen