Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Matthew D. Liptak


IsdG is a member of the heme acquisistion pathway of Staphylococcus aureus that catalyzes heme degradation leading to staphylobilin and formyl-oxo-bilin products. IsdG also plays role in heme biosynthesis. Monooxygenation of heme via IsdG forms a meso-hydroxyheme, which is also formed by eukaryotic heme oxygenases. Recent findings indicated the involvement of a ferryl=oxoheme intermediate in the heme degradation mechanism of IsdG. We employed spectroscopic characterization techniques to analyze an analogue for this ferryl form to gain insight into the mechanism of heme hydroxylation by IsdG. The formation of a sufficiently long-lived, unique ferryl=oxoheme after one minute of reaction between heme bound IsdG and 10 equivalents of meta chloroperbenzoic acid (mCPBA) was characterized using UV/Vis absorption, magnetic circular dichroism (MCD) and electron paramagnetic resonance (EPR) spectroscopies. The MCD and EPR data indicated the presence of a ferryl=oxo center with S=1 and an organic radical. 13C-enriched samples were prepared and characterized using EPR spectroscopy. These experiments revealed the presence of a protein radical, not a porphyrin radical. When interpreted within the framework of hybrid quantum mechanics/molecular mechanics and time-dependent density functional theory calculations, analysis of the UV/Vis Abs spectrum suggested the presence of a deprotonated oxo ligand. Thus, the ferryl=oxoheme analogue of IsdG is assigned to as Compound ES with a Trp radical. The role second sphere interactions for Asn7 and Trp67 residues is further studied through spectroscopic analysis of the changes to the ferryl=oxoheme lifetime and its electronic structure. These data have important implications for the enzymatic mechanism of IsdG.



Number of Pages

150 p.

Available for download on Friday, December 06, 2024