Ether Oxidation by an Evolved Fungal Heme-Peroxygenase: Insights into Substrate Recognition and Reactivity.

Raul Mireles,Joaquin Ramirez-Ramirez,Miguel Alcalde,Marcela Ayala

doi:10.3390/jof7080608

Abstract

Ethers can be found in the environment as structural, active or even pollutant molecules, although their degradation is not efficient under environmental conditions. Fungal unspecific heme-peroxygenases (UPO were reported to degrade low-molecular-weight ethers through an H2O2-dependent oxidative cleavage mechanism. Here, we report the oxidation of a series of structurally related aromatic ethers, catalyzed by a laboratory-evolved UPO (PaDa-I) aimed at elucidating the factors influencing this unusual biochemical reaction. Although some of the studied ethers were substrates of the enzyme, they were not efficiently transformed and, as a consequence, secondary reactions (such as the dismutation of H2O2 through catalase-like activity and suicide enzyme inactivation) became significant, affecting the oxidation efficiency. The set of reactions that compete during UPO-catalyzed ether oxidation were identified and quantified, in order to find favorable conditions that promote ether oxidation over the secondary reactions.

Highlights

The ether functional group is commonly found in nature as metabolites, structural polymers, oil-derivatives or bioplastics, among others
We found that aromatic ethers are not efficiently transformed by PaDa-I; the magnitude of secondary, unproductive reactions occurring simultaneously during aromatic ether oxidation was quantified, in order to adjust reaction conditions so that ether oxidation was favored
In order to study if the chemical nature of substituents in aromatic ethers influenced its oxidation by PaDa-I, a series of five compounds with increasing polarity was selected, as shown in Scheme 1A

Summary

Introduction

The ether functional group is commonly found in nature as metabolites, structural polymers, oil-derivatives or bioplastics, among others. They can be found as active molecules in many man-made products, such as agrochemicals, cosmetics, detergents or drugs [1,2]. Some of them can be identified as pollutants due to their characteristic capability to remain chemically intact and still active in environmental conditions [5] (EPA, 2009). Their recalcitrant character is mainly due to the high stability of the ether bond. The energy needed for C–O bond dissociation in ethyl propyl ether (84.8–85.3 kcal/mol) is similar to that required for a

Methods

Results

Conclusion