Abstract
Type I Baeyer–Villiger monooxygenases (BVMOs) are flavin-dependent monooxygenases that catalyze the oxidation of ketones to esters or lactones, a reaction otherwise performed in chemical processes by employing hazardous and toxic peracids. Even though various BVMOs are extensively studied for their promising role in industrial biotechnology, there is still a demand for enzymes that are able to retain activity at high saline concentrations. To this aim, and based on comparative in silico analyses, we cloned HtBVMO from the extremely halophilic archaeon Haloterrigena turkmenica DSM 5511. When expressed in standard mesophilic cell factories, proteins adapted to hypersaline environments often behave similarly to intrinsically disordered polypeptides. Nevertheless, we managed to express HtBVMO in Escherichia coli and could purify it as active enzyme. The enzyme was characterized in terms of its salt-dependent activity and resistance to some water–organic-solvent mixtures. Although HtBVMO does not seem suitable for industrial applications, it provides a peculiar example of an alkalophilic and halophilic BVMO characterized by an extremely negative charge. Insights into the behavior and structural properties of such salt-requiring may contribute to more efficient strategies for engineering the tuned stability and solubility of existing BVMOs.
Highlights
The transformation of ketones to esters or lactones by peracids is known as Baeyer–Villiger oxidation
We looked for putative Baeyer–Villiger monooxygenases (BVMOs), focusing on organisms that are unusual for this enzyme class, e.g., extremophiles
We identified a putative BVMO from the extremely halophilic archaeon Haloterrigena turkmenica: HtBVMO
Summary
The transformation of ketones to esters or lactones by peracids is known as Baeyer–Villiger oxidation. Organic peracids are strong oxidants and display poor selectivity. Their use may lead to the formation of the corresponding carboxylic acid salt as waste, which has to be recycled or disposed of [2]. Among the alternative methods, which aim to bypass both the environmental and safety issues associated with the chemical approach, the use of Baeyer–Villiger monooxygenases (BVMOs) as biocatalysts for Baeyer–Villiger oxidations represents one of the most attractive approaches. BVMOs are flavoenzymes, which utilize molecular oxygen, instead of a peracid, as the stoichiometric oxidant and often exhibit a Catalysts 2020, 10, 128; doi:10.3390/catal10010128 www.mdpi.com/journal/catalysts
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
