Unravelling the structure-function relationship of heme proteins - Spectroscopic studies of their redox-active sites
25 September 2020
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Department of Physics
Sabine Van Doorslaer
ONLINE PhD defence Kevin NYS - Faculty of Science, Department of Physics
Heme-containing proteins are omnipresent in all kingdoms of life and display a striking versatility. While the function of heme proteins is largely determined by the protein fold dictating the active site architecture, accessibility and redox properties, there is no one-on-one relationship linking a particular protein structure with a specific function. In this work, I studied two types of heme proteins, observing how structural elements and subtle changes are able to tune the functional role. To this end, optical spectroscopy and electron paramagnetic resonance were employed as they are able to selectively probe the redox-active sites of heme proteins.
Dye-decolorizing peroxidases are heme-containing oxidoreductases of bacterial and fungal origin. They catalyze the hydrogen-peroxide-mediated oxidation of bulky textile dyes and lignin model compounds. A combined biochemical and biophysical approach was used here providing better understanding of the catalytic properties of this protein class, paving the way for applications in waste water treatment and biomass conversion. The roles of the distal amino acid residues in a subclass of dye-decolorizing peroxidases were elucidated and the accessibility of the active site was thoroughly examined. This also resulted in some hands-on advice for future EPR spectroscopic studies on heme proteins.
Moreover, a persistent organic radical in the resting state of a dye-decolorizing peroxidase was observed and characterized in this work, utilizing a highly fruitful strategy which combines computational predictions and spectroscopic experiments. The discovery of a dyad motif provided the first report of a stable radical in the resting state of a heme peroxidase.
Another heme protein concerned in this work is hemoglobin. While the latter is commonly known for its role in oxygen transport, it is intriguing that hemoglobin is also found in insects which breathe through a tracheal respiratory system. I performed a spectroscopic study on hemoglobin from the European honeybee and the malaria mosquito, showing some surprising differences in their heme cavity, ligand affinity and proposed function despite a similar living environment.