Enzymatic Mechanism of Oxalate Decarboxylase Revealed by Biophysical and Structural Studies

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With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Alexander Angerhofer from the University of Florida to investigate the degradation of oxalic acid by an enzyme known as oxalate decarboxylase which is found in soil bacteria and fungi. Overloading the body with oxalic acid can lead to kidney stones and other adverse health effects in animals and humans. As a plant product oxalic acid is present in many plant-derived foods in appreciable quantities. A way to keep the amount of oxalic acid low is to decompose it by chemical reactions catalyzed by enzymes. The research of Dr. Angerhofer is focused on the elucidation of the mechanism by which the enzyme oxalate decarboxylase breaks down oxalic acid. More specifically, Dr. Angerhofer will test the hypothesis that to decompose oxalic acid, this protein transfers electrons over a long distance, about 2 nm, between two manganese ions, one of which is located at the active site for the chemical transformation of oxalic acid. This study will involve use of a combination of advanced biochemical methods of protein engineering with structural and spectroscopic methods, including X-ray crystallography, electron paramagnetic resonance, and optical spectroscopy. The results of this research will enhance our fundamental knowledge of reactions that involve bio-active manganese and will ultimately aid in devising strategies to mitigate the presence of oxalic acid in plants. The project supports the training of a growing and diverse science and technology workforce in the state of Florida by involving students in research that helps them acquire scientific and professional skills useful in the bio-economy of the 21st century. The training of undergraduate students is supported through a course-based undergraduate research experience at the University of Florida and through the University Research Scholars Program, which brings gifted freshmen students to the cutting edge of modern research.This award supports the research of Dr. Angerhofer focused on the study of the molecular mechanisms by which the bacterial enzyme oxalate decarboxylase catalyzes the cleavage of the kinetically inert carbon-carbon bond in oxalic acid. It has been proposed that long-range electron transfer between the manganese ions situated at the N- and the C-terminal ends of the proteins subunits plays an important catalytic role. X-ray crystallography, molecular dynamics simulations, electrochemistry, and an array of advanced electron paramagnetic resonance (EPR) technologies, in combination with site-directed mutagenesis will be applied to the problem. The activity of manganese ions in the protein and a chain of electron transfer-active amino acids will be studied. Genetic code expansion methods will be used to introduce unnatural amino acids into the enzyme at specific target sites where they can be used to probe a long-range electron transfer pathway that may exist in the quaternary structure of the enzyme. The planned experiments will yield important structural and kinetic information about substrate and oxygen co-factor binding to the enzyme. The hypothesis that will be tested is that via long-range electron transfer dioxygen promotes catalysis by generating the +3 oxidation state on the active-site Mn ion situated at the N-terminal end, which in turn drives the reaction. The proposed work will elucidate how proteins tune and utilize the redox potential of mono-nuclear Mn centers for catalysis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.