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Special Guest Speaker
Dr. Christopher Colbert
Chemistry and Biochemistry
North Dakota State University
Understanding Structure and Mechanism of Metalloproteins
to Identify Novel Bio-Based Solutions
Metalloproteins comprise approximately one-third of all proteins, and are
critical for many of the biochemical processes responsible for life. Our longterm goal is to elucidate how cells import, incorporate, and utilize metals within
proteins by using a combination of structural, biophysical, biochemical and
molecular biology approaches. I will present two distinct projects in which we
investigate how iron is used for biochemical processes involved in regulation
of enzyme catalysis and gene expression to address challenges faced by
modern human societies.
Project 1: Rieske oxygenases are a diverse class of non-heme, mononuclear
iron-containing enzymes capable of the stereo- and regio-selective insertion of
molecular oxygen into aromatic substrates. These enzymes are important in
the bioremediation of polyaromatic hydrocarbons and polychlorinated biphenyls (PCBs). However, only
a few, such as biphenyl 2,3-dioxygenase from Pandoraea pnomenusa B-356 (BPDO), can potently
degrade a large variety of PCB congeners. We have elucidated the structural basis for the broad PCB
oxidation properties of BPDO, based on information from our structural studies combined with activity
assays of selected mutants. These properties are probably rooted in the enzyme’s evolutionary
interaction with secondary plant metabolites such as flavonoids. Our recent unpublished results
suggest that the potent aromatic oxidizing properties of BPDO can be directed toward plant byproducts
to make hydroxylated compounds with potentially two or three chiral centers, which may be exploited
in natural product synthesis.
Project 2: Cell-Surface Signaling (CSS) pathways in Gram-negative bacteria allow the cell to respond
to extracellular stimuli. CSS pathways often involve three distinct proteins, 1) an outer membrane
extracellular receptor, responsible for sensing the stimuli, 2) an inner membrane sigma factor regulator
that transduces the signal from the periplasm to the cytoplasm, and a cytosolic sigma factor, which
performs transcriptional regulation of stimulus response genes. A CSS pathway facilitates strict control
of intracellular iron levels. Binding of an extracellular iron-laden siderophore to an outer membrane
TonB-dependent transporter (TBDT) triggers CSS by inducing proteolytic degradation of the inner
membrane sigma regulator. This releases the transcription factor to up-regulate transcription of the
TBDT. We are investigating the Pseudomonas putida WCS358 pseudobactin BN7/8 system to
understand this conserved process. Our studies reveal unique structural features with novel
mechanistic implications for CSS. This information will guide future efforts to improve delivery of
antibiotics to Gram-negative bacteria.
February 20, 2017
3:00 PM
ENV 125