Mechanisms of (regio)-chemoselectivity of iron-enzymes that catalyze the non-canonical decarboxylation of fatty acids in hydrocarbon biosynthesis

Abstract

The decline in fossil resources along with massive energy consumption have led to an increasing global warming crisis. Climate change has generated a huge debate and serious concerns regarding the continued dependence on fossil fuels and petrochemicals. Hydrocarbon-based biofuels can be a suitable replacement for fossil-based ones, while hydrocarbons also feature prominently as chemical building blocks in the production of a range of products, particularly polymers and plastics. Metalloenzymes play a crucial role in the hydrocarbons production, and the last decade has witnessed the discovery of enzymes that catalyze the decarboxylation of fatty acids into hydrocarbons, employing non-canonical oxidative mechanisms that lead to C-C bond scission en route. There is substantial diversity in structure, mode of action, need for cofactors and substrate scope among these metalloenzymes, which are generally divided between: heme-monoxygenases and iron-dependent mono- and dinuclear oxygenases. The comprehension of such mechanisms is essential for the successful implementation of these enzymes in cell-free and cell factory biotechnological systems through synthetic biology approaches. In this sense, recently, our group contributed to the discovery and understanding of a new decarboxylase from the heme-protein family that has superior functional aspects of turnover, stability, substrate scope and performs the catalysis through mechanisms distinct from those reported to date. In this project, we will be continuing this research, focusing on the mechanistic study of iron-dependent non-heme enzymes. These are decarboxylases that act in the absence of a cofactor, producing mainly 1-undecene (UndA). Given this, we will try to determine the catalytic mechanisms by which UndAs activate dioxygen for the hydrocarbon biosynthesis. Through a multidisciplinary approach, we intend to answer the following questions: Are UndAs chemoselective for hydroxylation (canonical)? Are UndAs specific for different fatty acids' length? Does oligomerization play a role in catalysis? Are there any natural redox partners? Does the iron-dependent core hold one or two irons? At the end of the project, we will be able to have a detailed understanding of the mechanisms of heme and non-heme enzymes in the non-canonical decarboxylation of fatty acids, in addition to contributing to the advancement of biological routes to obtain biohydrocarbons. (AU)