Impacts of the oxidizable scaffold of catalase-peroxidase (KatG): Modulation of a heme peroxidase for catalytic versatility

Abstract

Catalase-peroxidase (KatG) is an antioxidant protein that plays a key role in the degradation of H2O2 for pathogenic and non-pathogenic bacteria and lower eukaryotes. Despite having the general structure of a heme peroxidase, KatG displays functionality distinct from a typical heme peroxidase. Two prominent examples are robust catalase activity and activation of antitubercular pro-drug isoniazid. Alongside other variations from the typical heme peroxidase scaffold, the astounding abundance of oxidizable residues within the protein structure of KatG, especially within the active-site containing N-terminal domain, seem to play a central role in the conversion of a heme peroxidase to a multifunctional enzyme. The plethora of redox-active residues within its protein structure has at least facilitated a mechanism by which KatG has converted protein oxidation from a detrimental phenomenon to a net catalytic benefit. In particular, oxidation of three active-site residues results in the formation of a KatG-unique post-translational modification (i.e., MYW adduct) near the heme center. Redox cycling of this MYW adduct between its fully-covalent and free-radical states supports robust catalase activity from an otherwise poorly catalase-active, heme-peroxidase active site. Simultaneously, the oxidation of the many Tyr, Trp, and Met positioned throughout the KatG scaffold provide hole-hopping pathways supports a unique peroxidase mechanism that functions to preserve the active site for catalase activity. The work presented here aims to better understand the heme intermediates involved in peroxidase and catalase mechanisms of KatG (Chapters 2 and 3) in addition to investigating other functionalities of the enzyme including the biosynthesis of the MYW adduct of KatG and isoniazid activation (Chapters 4 and 5). Understanding the relationship between structure and function of KatG is likely to inform the processes and mechanisms by which enzymes, particularly oxidoreductases, gain novel catalytic function. This work was supported by a grant from the National Science Foundation (MCB 1616059).