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Functional and structural analysis of catalase-phenol oxidase from scytalidium thermophilum

Yüzügüllü, Yonca
Scytalidium thermophilum produces a novel phenol oxidase, which has turned out to be a bifunctional catalase-phenol oxidase (CATPO) during the course of this work, by other researchers of our group. Therefore, in the beginning of the studies, substrate specificity and inhibitor assays were conducted on the crude enzyme, followed by production, purification, cloning, expression, and mutagenesis and crystallography studies for further functional and structural analysis of CATPO. Accordingly, substrate specificity and inhibitory tests applied for crude enzyme characterisation presented the similarity of the phenol oxidase nature of CATPO essentially to catechol oxidase. Production studies were performed to investigate the effects of different factors including induction time, growth temperature, exogenous iron and hydrogen peroxide addition. In view of that, CATPO is constitutively produced in a growth associated manner. However, some phenolic compounds enhance its production. In this study, 15 phenolic compounds were tested for their ability to affect CATPO production. Of the phenolic compounds tested, catechol, resorcinol and vanillic acid caused repression of CATPO production. On the other hand, caffeic acid, myricetin and resveratrol enhanced CATPO production. As a biocatalyst, the efficiency of CATPO was examined and found to be a good candidate for getting pharmaceutically important drug intermediates. Its dual mechanism was analysed through side-directed mutagenesis. Two conserved residues (His101 and Val142) were mutated to discriminate catalase and phenol oxidase activities. Spectroscopic and mutagenesis studies exhibited the presence of heme d centre. Lastly, its structure was analysed by X-ray crystallography and found to have a tetrameric structure.