The broad focus of our research is to discover the mechanisms of enzymes bearing metal cofactors. Specifically, we work with several different groups of enzymes which mainly rely on iron and molecular oxygen to accomplish interesting chemistry.

One such family is the iron(II) and 2-oxoglutarate (2OG) dependent enzymes, which are the most common type of nonheme mononuclear iron dependent enzymes. They are present in all three domains of life and highly represented in the biosynthetic pathways for many molecules of varied medicinal and pharmaceutical interests. They use 2OG, a simple common metabolite, and molecular oxygen to generate a reactive, Fe(IV)-oxo intermediate called a ferryl. The ferryl can target a specific, unactivated C-H bond on the prime substrate for hydrogen atom transfer, generating a substrate radical. Most commonly, the radical will recombine with the ferryl oxygen to complete a hydroxylation reaction. However, the substrate radical can also be processed in alternative ways to achieve any of a variety of other oxidative outcomes. Over the last few decades, our lab has been a key player in this area of research, pioneering initial characterization of the ferryl intermediate and the reaction kinetics. We have since delineated reaction pathways leading to halogenation, desaturation, stereoinversion, oxacyclization, and endoperoxide insertion. Current work continues to expand understanding of the exquisite mechanistic control exhibited in these systems.

Enzymes which utilize two iron centers represent another thrust of our research.  Coupling two redox centers allows dinuclear oxygenases to catalyze a variety of oxidative transformations (such as the cleavage of unactivated O-H, C-H, C-C, C-P and N-H bonds). Consequently, these enzymes also play important roles in a number of biological pathways and are essential in the biosynthesis of certain antibiotics and anti-cancer theraputics. In other cases, dinuclear oxygenases act as valuable drug targets, necessitating study of their structure and mechanisms. The canonical dinuclear oxygenase has a ferritin-like fold and employs a diferrous cofactor to carry out one- or two-electron oxidations of their organic substrates. This includes enzymes such as soluble methane monooxygenase, class I-a ribonucleotide reductase and stearoyl- acyl carrier protein D9-desaturase. In recent years the repertoire of dinuclear oxygenases has expanded to include other structural classes, such as the heme oxygenase-like diiron oxygenases (HDOs) and HD-domain mixed-valent diiron oxygenases (HD-MVDOs). Different dimetal cofactors have also been identified. HD-MVDOs enrich and use a Fe2II/III cofactor to carry out 4-electron oxidative cleavages of substrates such as myo-inositol (MIOX) and organic phosphonates (PhnZ and TmpB). Meanwhile, different classes of ribonucleotide reductases (RNRs) have been shown to use iron-manganese and even dimanganese cofactors.

Ribonucleotide reductases are another major research area for our lab, named for their role in the de novo biosynthesis of 2’-deoxyribonucleotides (dNTPs), utilized for DNA replication and repair in all organisms.  RNRs can be divided into three main classes based on the identity of the metallocofactor that they use to initiate chemistry. We primarily focus on class I RNRs, the primary source of dNTPs in aerobic organisms, and characterization of their active cofactors.  While most characterized class I RNRs utilize a dinuclear metallocofactor and/or Tyr-derived radical, more recent discoveries have identified strategies employed by bacteria to limit their dependence on transition metals, such as use of Mn instead of Fe (class Ib-d) or ability to turnover with no metals present (class Ie). Historically, our lab and our collaborators have been key players in this area, and the focus our current enterprise includes the discovery and characterization of novel class I RNR cofactors.

Research at the intersection of chemistry and biology is necessarily interdisciplinary, and bioinorganic chemistry at Penn State is made strong by a high number of collaborations both internal and external. In order to explore fundamental mechanistic questions about the enzymes we study, we employ a wide variety of techniques including, but not limited to, cloning and other DNA manipulation techniques, protein overexpression and purification, chemical synthesis of substrates and substrate analogues, mass spectrometry, EPR and Mossbauer spectroscopy, X-ray crystallography, and rapid kinetics techniques such as freeze and chemical quench and stopped flow UV-vis spectroscopy.