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Professor of Chemistry and of Biochemistry and Molecular Biology
Carsten Krebs

Professional Appointments

Professor of Chemistry

Professor of Biochemistry and Molecular Biology


332 Chemistry Building
University Park, PA 16802
(814) 865-6089


Bollinger Krebs Group

Honors and Awards

SBIC Early Career Award, 2012

Camille Dreyfus Teacher Scholar, 2006-2011

Beckman Young Investigator, 2005-2008

Pfizer Award in Enzyme Chemistry, 2008


Bioinorganic Chemistry - spectroscopic and kinetic studies on the mechanisms of iron-containing enzymes

Enzymes that contain the transition metal iron in their active sites exhibit great structural and functional diversity and play important roles in almost every aspect of life. The goal of our interdisciplinary research program is to combine biochemical, kinetic, and spectroscopic methods to study Fe-containing enzymes. The main technique used in our laboratory is 57Fe-Mössbauer spectroscopy. This technique provides information about oxidation state, spin state, coordination environment, and nuclearity of all chemically distinct iron species contained in a sample. In addition, it is possible to quantify all iron species. We combine this method with the rapid freeze quench (RFQ) method, and this allows us to monitor changes occuring at an iron site during a biochemical reaction. These studies (in conjunction with other techniques, such as stopped-flow absorption or RFQ EPR) provide detailed insight into the reaction mechanisms of iron-containing proteins.

Non-heme enzymes

Our main focus in this area involves enzymes that utilize a mononuclear or dinuclear non-heme-iron cofactor to activate dioxygen (or a partially reduced form thereof) to create potent reaction intermediates capable of performing difficult oxidation reactions. The Bollinger/Krebs joint group focuses on studying these reactions with a combination of kinetic, analytical, and various complementary spectroscopic methods by trapping and characterizing reaction intermediates.

Iron-sulfur cluster enzymes

Our main focus in this area is the study of the ‘Radical-SAM’ enzymes. These enzymes utilize a reduced [4Fe-4S] cluster to cleave S-adenosylmethionine (SAM) to methionine and a 5’-deoxyadenosylradical (5’-dAdo·) intermediate. The 5’-dAdo· is then used for various purposes. We study several "Radical SAM" enzymes (in most cases in collaboration with Squire Booker's group) by using 57Fe-Mössbauer spectroscopy.

Selected Publications

Zhang, B.; Arcinas, A. J.; Radle, M. I.; Silakov, A.; Booker, S. J.; Krebs, C. “The First Step in Catalysis of the Radical S-Adenosylmethionine Methylthiotransferase MiaB Yields an Intermediate with a [3Fe-4S]0-like Auxiliary Cluster” J. Am. Chem. Soc. 2020, accepted.

Dunham, N. P.; Del Río Pantoja, J. M.; Zhang, B.; Rajakovich, L. J.; Allen, B. D.; Krebs, C.; Boal, A. K.; Bollinger, J. M., Jr. “Hydrogen Donation but not Abstraction by a Tyrosine (Y68) During Endoperoxide Installation by Verruculogen Synthase (FtmOx1)” J. Am. Chem. Soc.  2019, 141, 9964-9979.

Blaesi, E. J.; Palowitch, G. M.; Hu, K.; Kim, A. J.; Rose, H. R.; Alapati, R.; Lougee, M. G.; Kim, H. J.; Taguchi, A. T.; Tan, K. O.; Laremore, T. N.; Griffin, R. G.; Krebs, C.; Matthews, M. L.; Silakov, A.; Bollinger, J. M., Jr.; Allen, B. D.; Boal, A. K. “Metal-Free Class Ie Ribonucleotide Reductase from Pathogens Initiates Catalysis with a Tyrosine-Derived Dihydroxyphenylalanine Radical” Proc. Natl. Acad. Sci., U. S. A., 2018, 115, 10022-10027. 

Dunham, N. P.; Chang, W.-c.; Mitchell, A. J.; Martinie, R. J.; Zhang, B.; Bergman, J. A.; Rajakovich, L. J.; Wang, B.; Silakov, A.; Krebs, C.; Boal, A. K.; Bollinger, J. M., Jr. “Two Distinct Mechanisms for C-C Desaturation by Iron(II)- and 2-(Oxo)glutarate-Dependent Oxygenases: Importance of alpha-Heteroatom Assistance” J. Am. Chem. Soc. 2018, 140, 7116–7126.

Pan, J.; Bhardwaj, M.; Zhang, B.; Chang, W.-c.; Schardl, C. L.; Krebs C.; Grossman, R. B.; Bollinger, J. M., Jr. “Installation of the Ether Bridge of Lolines by the Iron- and 2-Oxoglutarate-Dependent Oxygenase, LolO: Regio- and Stereochemistry of Sequential Hydroxylation and Oxacyclization Reactions” Biochemistry 2018, 57, 2074-2083.

Kenney, G. E.; Dassama, L. M. K.; Pandelia, M.-E.; Gizzi, A. S.; Martinie, R. J.; Gao, P.; DeHart, C. J.; Schachner, L. F.; Skinner, O. S.; Ro, S. Y.; Zhu, X.; Sadek, M.; Thomas, P. M.; Almo, S. C.; Bollinger, J. M., Jr.; Krebs, C.; Kelleher, N. L.; Rosenzweig, A. C. “The Biosynthesis of Methanobactin” Science  2018, 359, 1411-1416.

Martinie, R. J.; Pollock, C. J.; Matthews, M. L.; Bollinger, J. M., Jr.; Krebs, C.; Silakov, A.  “Vanadyl as a Stable Structural Mimic of Reactive Ferryl Intermediates in Mononuclear Nonheme-Iron Enzymes” Inorg. Chem.  2017, 56, 13382–13389.

Mitchell, A. J.; Dunham, N. P.; Martinie, R. J.; Bergman, J. A.; Pollock, C. J.; Hu, K.; Allen, B. D.; Chang, W.-c.; Silakov, A.; Bollinger, J. M., Jr.; Krebs, C.; Boal, A. K.  “Visualizing the Reaction Cycle in an Iron(II)- and 2-(Oxo)-glutarate-Dependent Hydroxylase” J. Am. Chem. Soc. 2017, 139, 13830–13836.

Tamanaha, E.; Zhang, B.; Guo, Y.; Chang, W.-c.; Barr, E. W.; Xing, G.; St.Clair, J.; Ye, S.; Neese, F.; Bollinger, J. M., Jr.; Krebs, C.  “Spectroscopic evidence for the two C-H-cleaving intermediates of Aspergillus nidulans isopenicillin N synthase” J. Am. Chem. Soc. 2016, 138, 8862-8874.

Rajakovich, L. J.; Nørgaard, H.; Warui, D. M.; Chang, W.-c.; Booker, S. J.; Krebs, C.; Bollinger, J. M., Jr.; Pandelia, M.-E. “Rapid Reduction of the Diferric-Peroxyhemiacetal Intermediate in Aldehyde-Deformylating Oxygenase by a Cyanobacterial Ferredoxin: Evidence for a Free-Radical Mechanism” J. Am. Chem. Soc.  2015, 137, 11695-11709.

Bollinger, J. M., Jr.; Chang, W.-c.; Matthews, M. L.; Martinie, R. J.; Boal, A. K.; Krebs, C. “Mechanisms of 2-Oxoglutarate-Dependent Oxygenases: The Hydroxylation Paradigm and Beyond” in “2-Oxoglutarate-Dependent Oxygenases” Hausinger, R. P. and Schofield, C. J.; The Royal Society of Chemistry, London, 2015, 95-122.

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, 1140-1144.

Krebs, C., Bollinger, J. M., Jr.; Booker, S. J. "Cyanobacterial alkane biosynthesis expands the functional and mechanistic repertoire of the "di-iron-carboxylate" proteins," Current Opinion Chem. Biol., 2011, 15, 291-303.

van der Donk, W. A.; Krebs, C.; Bollinger, J. M., Jr. "Substrate activation by iron superoxo intermediates," Current Opinion Struct. Biol., 2010, 20, 673–683.

Krebs, C.; Galonić Fujimori, D.; Barr, E. W.; Walsh, C. T.; Bollinger, J. M., Jr. "Non-heme Fe(IV)-Oxo Intermediates," Acc. Chem. Res., 2007, 40, 484-492.

Jiang, W.; Yun, D.; Saleh, L.; Barr, E. W.; Xing, G.; Hoffart, L. M.; Maslak, M.-A.; Krebs, C.*; Bollinger, J. M., Jr.* "A Stable Manganese(IV)/Iron(III) Cofactor Initiates Substrate Radical Production in Chlamydia trachomatis Ribonucleotide Reductase," Science, 2007, 316, 1188-1191.

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 a-Ketoglutarate-Dependent Dioxygenase: A High-Spin Fe(IV) Complex in Taurine/a-Ketoglutarate Dioxygenase (TauD) from Escherichia coli," Biochemistry 2003, 42, 7497-7508.