216 GHz Electron Paramagnetic Resonance of Mycobacterium Tuberculosis Catalase-Peroxidase: The Role of the Arg418 Residue
The catalase-peroxidase protein from Mycobacterium tuberculosis contains a variety of unique structural features including a covalently-linked three amino acid adduct capable of hosting a tyrosine-based radical. Previous work has demonstrated that the Arg418 residue is essential for the catalse but not the peroxidase activity of the protein and crystallography has indicated the residue to be capable of adopting two conformations relative to the adduct-radical. In the present work the WT and Arg418Leu mutant proteins were investigated using high-field electron magnetic resonance spectroscopy. Different sets of g-values were found for each protein indicating different paramagnetic environments. Quantum chemical calculations of model structures were undertaken to elucidate the geometrical environment of the radical. It is proposed that the two sets of g-values correspond to the two conformations of the Arg418 residue. The implications for the catalytic mechanism are discussed.