The Role of Geometric Structure in Avoidance of Oxygen Rebound to Enable Aliphatic Halogenation and Oxacyclization by Non-heme Fe(IV)-oxo (ferryl) Complexes

The iron and 2-oxo-glutarate dependent (Fe/2OG) oxygenases catalyze a wide range of reactions such as hydroxylation, halogenation, stereoinvesion, ring expansion, desaturation and cyclization. Our published work demonstrates the ability of many representatives of Fe/2OG oxygenases to divert reactivity from one outcome to another depending on the presented substrate analogs and modifications in the immediate amino acid surrounding. Moreover, in such cases as oxacyclases and desaturases, the same enzyme is able to perform two or more sequential transformations on the substrate with different outcomes. All transformations above involve H• abstraction by Fe(IV)-O intermediate. It is not understood how enzymes of this family divert the reaction to non-hydroxylated outcomes following the installation of the Fe(III)-OH and substrate-carbon radical. Our primary hypothesis is that the structural plasticity of the metallocofactor allows perturbing the potential landscape of different reaction pathways in favor of the desired outcome. To address this hypothesis, we will elucidate the reaction mechanisms of representatives of two subclasses of these enzymes, halogenases and oxacyclases. We will employ advanced spectroscopic and crystallographic methods to establish precise metrics of substrate - metallocofactor structural relationship that will ultimately provide a unified atom- level understanding of the divergent reactivity of Fe/2OG oxygenases. Fe/2OG oxygenases are implicated in biosynthetic pathways for a large number of important natural products such as drugs and antibiotics. Gaining a predictive understanding of the reaction mechanisms will provide unprecedented control over the reaction outcomes and set the stage for re-engineering these systems to perform customized reactions expanding the library of available natural products for specific medicinal and scientific needs.