Enzymes are the tiny helpers of industrial biotechnology. Despite their microscopic size, they need to be tough and diligent because we want them to catalyze a broad range of reactions, ideally with the speed of light for ever after. In reality, however, many enzymes are like sensitive creatures, who need most careful attention and special treats to get their nicest behavior. Otherwise they might fade away like a tender flower in the blinking sun and send the biotechnologists into terrible trouble. One strategy to find frugal enzymes is to look at thermophilic organisms. They sometimes harbor a treasure of more stable proteins because they are used to withstand somewhat unfriendly conditions such as high temperatures.

The thermophilic fungus Thermothelomyces thermophila is a treasure chest that is currently being investigated by a team of Dutch and Italian researchers in the frame of the ROBOX project that is particularly devoted on the development of possibly robust methods for the oxidation of industrially relevant compounds. One of the notoriously difficult reactions to be performed in chemical synthesis is the selective oxidation of compounds that is fuelled by air. Enzymes very often outperform chemical strategies in certain aspects. The so-called Baeyer-Villiger oxidation is a typical example for a reaction where chemical processes are faced with severe environmental and safety concerns: Enzymes are a pretty good alternative to selectively insert an oxygen into a C-C bond.

PokeMO: a promising starlet in the universe of Baeyer-Villiger Monooxygenases

The proteins whose destiny it is to catalyze Baeyer-Villiger type reactions are called Baeyer-Villiger Monooxygenases, in short BVMOs. Numerous BVMOs have been discovered and studied in the recent past. What remained problematic, however, was their poor solvent tolerance and thermostability. A more robust BVMO was urgently needed, most importantly one with an affinity for bulky substrates such as steroids, which are functionalized by only few BVMOs. The smart clue of the researchers was to built on the correlation between sequence similarity and substrate scope, which was recently unraveled at TUWien and to combine this knowledge with the genetic information about the thermophilic fungus T. thermophila. The identified sequence was then produced in E. coli using codon-optimization and fusion to a reductase that is needed to complete the catalytic cycle. Luckily, the fungal protein liked to be produced by the bacterial host very much and furthermore revealed its crystal structure to the structural biologists. As a catalyst, it outperformed other BVMOs with respect to stability and the ability to functionalize bulky compounds. PokeMO (polycyclic ketone monooxygenase) is a new BVMO prototype with potential to become an industrial biocatalyst.

Check out another article at the acib science blog in the frame of the ROBOX project! Robust enzymes – the main requirement for industrial applications