Halogenase

Scheme 9.38 Trichlorination of leucine with enzymes from the barbamide biosynthesis pathway (BarBl. BarB2 represent nonheme iron ketoglutarate-dependent halogenases).

Keller S, T Wage, K Hohaus, M Holzer, E Eichjorn, K-H van Pee (2000) Purification and partial characterization of tryptophan 7-halogenase (PrnA) from Pseudomonas fluorescens. Angew Chem Int Ed 39 2300-2302. 

Dong, C., Flecks, S., Unversucht, S. et al. (2005) Tryptophan 7-halogenase (PrnA) structure suggests a mechanism for regioselective chlorination. Science, 309, 2216-2219. 

Blasiak, L.G., Vaillancourt, F.H., Walsh, C.T. and Drennan, C.L. (2006) Crystal structure of the non-haem iron halogenase SyrB2 in syringomycin biosynthesis. Nature, 440, 368-371. 

Vaillancourt, FH., Vosburg, D.A. and Walsh, C.T. (2006) Dichlorination and bromination of a threonyl-S-carrier protein by the non-heme Fe(II) halogenase SyrB2. ChemBioChem, 7, 748-752. 

With the use of gene clusters of the natural products coronatine and kutznerides, the biosynthetic pathway of coronamic acid has also been elucidated by Walsh and coworkers. From the biosynthetic analyses, a nonheme Fe -dependent halogenase was identified as the chlorinating enzyme that converts L- //a-isoleucine to 7-chloroisoleucine. A second enzyme carries out a dehydrochlorination reaction to yield coronamic acid. The general biosynthetic pathway is shown below (Scheme 7). 

Rebeccamycin is an antitumor or antibiotic agent isolated from bacteria " and contains a maleimide indolocarbazole framework. The Trp units in this molecule are chlorinated at the C-7 position and a flavin-dependent halogenase was identified as the enzyme that carries out this chlorination (Scheme 10). " There are many other halogenating enzymes known in the literature and these enzymes are responsible for the syntheses of metabolites containing bromine, chlorine, and fluorine. ... 

For electron-rich substrates, nature often uses flavin-dependent halogenases (e.g. chlorotetracycline), vanadium haloperoxidases (snyderol, Figure 7.4) or heme-iron haloperoxidases (tetraiodothyronine. Figure 7.4) for this role (Figure 7.5). For electron-deficient molecules such as alkanes, mononuclear iron... 

FADH2 halogenases such as tryptophan 7-halogenase have been shown to catalyze regioselective halogenation of a wide range of indole derivatives and aromatic heterocycles, where a cofactor regeneration system has recently been developed to use only a catalytic amount of cofactors (Scheme 7.13) [52, 53]. 

R2 = amine, alkyl, nitrile Scheme 7.13 Halogenation of indoles by tryptophan 7-halogenase. 

Scheme 7.14 Tryptophan 7-halogenases to create novel indolocarbazoles.

Fig. 4.2 A ribbon diagram of tryptophan 7-halogenase, an enzyme important in the biosynthesis of pyrrolnitrin and rebeccamycin. (Photo K.-H. van Pee and J. H. Naismith)...

Abbreviated proposed mechanism of non-heme iron halogenase chlorination (1145, 1146, 2127, 2313, 2323). 

Vaillancourt FH, Yin J, Walsh CT (2005) SyrB2 in Syringomycin E Biosynthesis is a Nonheme Fen a-Ketoglutarate- and 02-Dependent Halogenase. Proc Natl Acad Sci USA 102 10111... 

Blasiak LC, Vaillancourt FH, Walsh CT, Drennan CL (2006) Crystal Structure of the Non-Haem Iron Halogenase SyrB2 in Syringomycin Biosynthesis. Nature 440 368... 

Hdlzer M, Burd W, Reissig H-U, van Pee K-H (2001) Substrate Specificity and Regio-selectivity of Tryptophan 7-Halogenase from Pseudomonas fluorescens BL915. Adv Synth Catal 343 591... 

Dong C, Kotzsch A, Dorward M, van Pee K-H, Naismith JH (2004) Crystallization and X-ray Diffraction of a Halogenating Enzyme, Tryptophan 7-Halogenase, from Pseudomonas fluorescens. Acta Cryst D60 1438... 

Yeh E, Gameau S, Walsh CT (2005) Robust in vitro Activity of RebF and RebH, a Two-Component Reductase/Halogenase, Generating 7-Chlorotryptophan During Rebeccamycin Biosynthesis. Proc Natl Acad Sci USA 102 3960... 

Eustaquio AS, Gust B, Luft T, Li S-M, Chater KF, Heide L (2003) Clorobiocin Biosynthesis in Streptomyces Identification of the Halogenase and Generation of Structural Analogs. Chem Biol 10 279... 

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