University of Natural Resources and Life Sciences, Vienna (BOKU) - Research portal

Logo BOKU Resarch Portal

Gewählte Doctoral Thesis:

Bernhard Gasselhuber (2016): Structural and Mechanistic Studies on Eukaryotic Catalase-Peroxidase.
Doctoral Thesis - Abteilung für Biochemie (DCH/BC), BOKU-Universität für Bodenkultur, pp 207. UB BOKU obvsg FullText

Data Source: ZID Abstracts
Abstract:
Bifunctional catalase-peroxidases (KatGs) have been shown to be part of Family I of the peroxidase-catalase superfamily and exhibit a peroxidatic activity as well as a highly efficient catalatic activity. By utilizing the robust extracellular KatG from the fungus Magnaporthe oryzae (grisea), we present the first high resolution crystal structure of a eukaryotic KatG in its ferric resting state as well as in the oxoiron(IV) state. The structures reveal several novelties compared to prokaryotic KatGs. Importantly, the two subunits of this homodimeric protein are crosswise intertwined by two highly conserved disulphide bridges, enhancing both the thermal and conformational stability of the eukaryotic representative. Beside heme b, KatGs carry a unique posttranslational modification very close to the active site, i.e. the so called covalent adduct autocatalytically formed between the three amino acids methionine, tyrosine and tryptophan (MYW adduct). It acts as an additional redox-active cofactor that is crucial for the catalatic reaction of KatGs. We confirm the essential role of the adduct as a radical site during hydrogen peroxide turnover and demonstrate that disruption of the adduct abolishes the catalase activity and converts the bifunctional enzyme to a monofunctional peroxidase. A conserved arginine residue far from the heme b but close to the covalent adduct additionally modulates the reactivity of the MYW adduct and in consequence the catalatic reaction of KatGs. Structural investigations confirm the pH dependent movement of the arginine side chain pointing either towards the adduct or away. This pH dependent interaction of the arginine with the adduct tyrosine is further supported by molecular dynamics simulations. Altogether, the structural and mechanistic findings allow to propose a mechanism of hydrogen peroxide dismutation that is in line with experimental data from both prokaryotic and eukaryotic catalase-peroxidases.

Betreuer: Obinger Christian
1. Berater: Oostenbrink Chris

© BOKU Wien Imprint