Project Abstract. Mononuclear nonheme iron (mnhFe) enzymes perform an array of chemically diverse
reactions that are vital to many different aspects of human health including: antibiotic biosynthesis, production
of key metabolites, and DNA repair. Thus, the misregulation and dysfunction of mnhFe enzymes have been
implicated in a number of disorders including neurodegeneration, cancers, diabetes, and cardiovascular
diseases. A large class of mnhFe enzymes contains a reduced Fe(II) ion that activates dioxygen, forming a highly
reactive FeIII-O2– species. Once formed, this FeIII-O2– intermediate can promote a large number of different
reactions leading to an enormous diversity in chemical reactivity. Despite the surprising similarities in active-site
(and sometimes substrate) structures, each enzyme promotes a highly specific reaction and yields a highly
specific product. The factors leading to such high reaction specificity from these similar active-site structures are
not fully understood. The overarching goal of the work proposed herein is to understand how the FeIII-O2–
intermediate in two mnhFe enzymes, cysteine dioxygenase (CDO) and isopenicillin-N-synthase (IPNS), can
selectively promote two vastly different reactions on structurally similar substrates: sulfur oxygenation (CDO) vs
C-H atom abstraction (IPNS).
Both CDO and IPNS modify a thiol-containing substrate once it is coordinated to the iron-center. We hypothesize
that the differential reactivity in these two enzymes is promoted by the orientation of the nominal S(3p)-type
orbital of the coordinated substrate, which will turn on or off a thermodynamically favored S-based oxygenation
reaction. To explore this hypothesis, we will prepare a library of structurally related metallopeptides that will
promote either CDO- or IPNS-like chemistries. The major difference between these peptides will be the
orientation of the S(3p)-type orbital relative to the vector of attack of the superoxo ligand of the FeIII-O2–
intermediate. Because the geometric and electronic structures of these peptides will all be nearly identical, all
differences in reactivity will be attributable to the S(3p) orbital orientation.
This research makes use of a large number of tools encountered in bioinorganic chemistry, thus providing an
excellent training platform for undergraduate researchers. In addition to biomimietic metallopeptide design and
synthesis, these systems will be subjected to mechanistic, spectroscopic (electronic absorption, EPR, (M)CD,
X-ray absorption, vibrational and Mössbauer spectroscopies), and high-level computational studies. The use of
metalloenzyme mimics in our investigations is especially noteworthy; few studies have been performed where
insight into specific biochemical processes are revealed through metallopeptide based metalloenzyme mimics.
Therefore, completion of this project will not only reveal interesting aspects of mnhFe biochemistry, but will also
expand the limits of investigations concerning metallopeptide based metalloenzyme mimics.
