Department of Biochemistry

Faculty of Medicine & Dentistry

University of Alberta

4-020 Katz Group - Rexall Centre for Pharmacy and Health Research

Edmonton, Alberta, Canada T6G 2E1

Tel: 780.492.2761

Lab Tel: 780.492.2558

Fax: 780.492.0886

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We seek an understanding of the structure and function of respiratory electron transfer enzymes at atomic resolution. Our strategy has been to select bacterial respiratory chain enzymes as model systems, to over-express them to high levels in the Escherichia coli inner membranes, and to subject them to intense biochemical, structural, and biophysical scrutiny. Our objectives are to: (a) obtain or utilize atomic-resolution structural data to generate models for respiratory energy conservation; (b) to use molecular genetics to probe redox-active cofactor communication and the influence of protein structure on cofactor function; and (c) to investigate the role of substrate binding sites in biological energy conservation. We focus on the following E. coli model systems:

Nitrate Reductase A (NarGHI) and DMSO Reductase (DmsABC) Nitrate reductase A (NarGHI) is an excellent model system to study protonmotive force generation by the redox loop mechanism. It has two substrate binding sites, one located in the cytoplasmic membrane, which releases protons into the periplasmic compartment as a result of quinol oxidation, and a nitrate reducing site that consumes cytoplasmically-localized protons as a result of nitrate reduction to nitrite. Catalytic turnover thus contributes to the protonmotive force across the cytoplasmic membrane. We are studying these two substrate-binding sites and the prosthetic groups that mediate electron transfer between them. Our efforts culminated in a 1.9Å resolution structure of the enzyme (in collaboration with Dr. Natalie Strynadka, UBC). We use electron paramagnetic resonance (EPR) to study NarGHI and other respiratory chain enzymes. Two spectrometers are located in the laboratory, a Bruker Elexys E500 equipped with a liquid helium cryogenic system is used to record spectra of hemes and [Fe-S] clusters, and a Bruker ESP300E equipped with a liquid nitrogen cryogenic system is used to record spectra of free radicals and molybdenum.

Bacterial Complex II Homologs Fumarate reductase (FrdABCD) and succinate dehydrogenase (SdhCDAB) are both excellent model systems for mitochondrial complex II. They are expressed anaerobically and aerobically, respectively, and have similar overall structures and prosthetic group compositions. Our focus with SdhCDAB is to understand the relationship between the identified ubiquinone binding site and the heme and [3Fe-4S] cluster to which it is in close juxtaposition. We are addressing these issues using a combination of site-directed mutagenesis and biochemical/ biophysical assays. In the case of FrdABCD, we are trying to determine the role of the menaquinol binding sites identified in the structure of the protein.

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