J. Martin Bollinger

Demystifying the chemical magic of non-heme-iron enzymes in natural product biosynthesis

Non-heme-iron (NH-Fe) enzymes activate O2 for an array of biomedically and agriculturally important oxidation reactions. Our past decade’s work has characterized iron(IV)-oxo (ferryl) complexes in several such NH-Fe enzymes.1 Most often, the ferryl complexes generate substrate radicals by abstracting hydrogen (H•) from aliphatic carbons,2-6 leading to formation of new C–O,2-4 C–Cl/Br,5 or C–S bonds.1 Motivated by our success in rationalizing the divergent outcomes of the NH-Fe 2-(oxo)glutarate-dependent aliphatic hydroxylases and halogenases,6 we now seek both to exploit the ferryl manifold for novel carbon-functionalization reactions7 and to explain the structural and mechanistic bases for several other natural reaction types, including dehydrogenation of an alcohol to epoxide,8 stereo-inversion of a chiral carbon,9 and desaturation and cleavage of C–C bonds, that are initiated by ferryl complexes in other NH-Fe enzymes. Insight obtained will inform combinatorial design of new antibiotic and anticancer drugs.

1. Krebs, C., Galonic, D.; Walsh, C. T.; Bollinger, J. M., Jr. “Non-Heme Fe(IV)-Oxo Intermediates,” Acc. Chem. Res., 2007, 40, 484-492.

2. Price, J. C.; Barr, E. W.; Tirupati, B.; Bollinger, J. M., Jr.; Krebs, C.; “The First Direct Characterization of a High-Valent Iron Intermediate in the Reaction of an Ketoglutarate-Dependent Dioxygenase: A High-Spin Fe(IV) Complex in Taurine:-Ketoglutarate Dioxygenase (TauD) from Escherichia coli,” Biochemistry, 2003, 42, 7497-7508.

3. Price, J. C.; Barr, E. W.; Glass, T. E.; Krebs, C.; Bollinger, J. M., Jr.; “Evidence for Hydrogen Abstraction from C1 of Taurine by the High-Spin Fe(IV) Intermediate Detected during Oxygen Activation by Taurine:-Keto-glutarate Dioxygenase (TauD),” J. Am. Chem. Soc., 2003, 125, 13008-13009.

4. Hoffart, L. M.; Barr, E. W.; Guyer, R. B.; Bollinger, J. M., Jr.; Krebs, C. “Direct spectroscopic detection of a C-H-cleaving high-spin Fe(IV) complex in a prolyl-4-hydroxylase,” Proc. Natl. Acad. Sci. USA, 2006, 103, 14738-14743.

5. Galonic, D. P.; Barr, E. W.; Walsh, C. T.; Bollinger, J. M., Jr.; Krebs, C. “Two Interconverting Fe(IV) Intermediates in Aliphatic Chlorination by the Halogenase CytC3,” Nat. Chem. Biol., 2007, 3, 113-116.

6. Matthews, M. L.; Neumann, C. S.; Miles, L. A.; Grove, T. L.; Booker, S. J.; Krebs, C; Walsh, C. T.; Bollinger, J. M., Jr. “Substrate positioning controls the partition between halogenation and hydroxylation in the aliphatic halogenase, SyrB2,” Proc. Natl. Acad. Sci. USA, 2009, 106, 17723-17728.

7. Matthews, M.L.; Chang, W.-c.; Layne, A.P.; Miles, L.A.; Krebs, C.; Bollinger, J.M., Jr. “Direct Nitration and Azidation of Aliphatic Carbons by an Iron-dependent Halogenase,” Nat. Chem. Biol. 2014, 10, 209-215.

8. Wang, C.; Chang, W. C.; Guo, Y.; Huang, H.; Peck, S.C.; Pandelia, M.E.; Lin, G.M.; Liu, H.W.; Krebs, C.; Bollinger, J.M., Jr. “Evidence that the Fosfomycin-Producing Epoxidase, HppE, Is a Non-Heme-Iron Peroxidase,” Science 2013, 342, 991-995.

9. Chang, W.-c.; Guo, Y.; Wang, C.; Butch, S. E.; Rosenzweig, A. C.; Boal, A. K.; Krebs, C.; Bollinger, J.M., Jr. “Mechanism of the C5 Stereoinversion Reaction in the Biosynthesis of Carbapenem Antibiotics,” Science 2014, 343, 1140-1143.