Runda, M. E. | bioRxiv Science

bioRxiv2024

Protein fusion strategies for a multi-component Rieske oxygenase

Rieske oxygenases (ROs) are enzyme systems involved in microbial biodegradation or late-stage modifications during natural product biosynthesis. A major obstacle to working with ROs is their dependence on multi-component electron transfer chains (ETCs). Thereby, electrons from NAD(P)H are shuttled directly via a reductase (Red) or indirectly via an additional ferredoxin (Fd) to a terminal oxygenase (Oxy) for oxygen activation and subsequent substrate conversion. The present work evaluates potential fusion strategies to simplify the ETC of the three-component cumene dioxygenase (CDO) from Pseudomonas fluorescence. In in vitro reactions, the fusion of CDO-Red to CDO-Fd is the most suitable for activation of CDO-Oxy with product formation of approximately 22 mM (72 % conversion). Furthermore, protein fusion to CDO-Oxy was found to be feasible, highlighting the versatility of the redox partner fusion approach. Overall, this study aims to contribute to the research field of ROs by providing a promising strategy to simplify their multi-component nature.

biochemistry↗

bioRxiv2024

Developing Hybrid Systems to Address O2 Uncoupling in Multi-Component Rieske Oxygenases

Rieske non-heme iron oxygenases (ROs) are redox enzymes that are essential for microbial biodegradation and natural product synthesis. These enzymes utilize molecular oxygen for oxygenation reactions, making them very useful in applied enzymology due to their broad reaction scope and high selectivities. The mechanism of oxygen activation in ROs involves electron transfers between redox centers of associated protein components, forming an electron transfer chain (ETC). Although the ETC is essential for electron replenishment, it carries the risk of reactive oxygen species (ROS) formation due to electron loss during oxygen activation. Our previous study linked ROS formation to O2 uncoupling in the flavin-dependent reductase of the three-component cumene dioxygenase (CDO). In the present study, we extend this finding by investigating the effects of ROS formation on the multi-component CDO system in a cell-free environment. In particular, we focus on the effects of hydrogen peroxide (H2O2) formation in the presence of a NADH cofactor regeneration system on the efficiency of CDO catalytic efficacy in vitro. Based on this, we propose the implementation of hybrid systems with alternative (non-native) redox partners for CDO, which are highly advantageous in terms of reduced H2O2 formation and increased product formation. The hybrid system consisting of the RO-reductase from phthalate dioxygenase (PDR) and CDO proved to be the most promising for the oxyfunctionalization of indene, showing a 4-fold increase in product formation (20 mM) over 24 h at a 3-fold increase in production rate compared to CDO-WT.

biochemistry↗