Spheroplasts preparation boosts the catalytic potential of a squalene-hopene cyclase

Squalene-hopene cyclase are membrane-bound enzymes used to produce bioactive compounds at industrial scale. Here, the authors show squalene-hopene cyclase spheroplasts, obtained by removing the outer cell membrane, having a higher catalytic activity than the enzymes and the whole cells, and their cross-linking for recycling and reuse. Squalene-hopene cyclases are a highly valuable and attractive class of membrane-bound enzymes as sustainable biotechnological tools to produce aromas and bioactive compounds at industrial scale. However, their application as whole-cell biocatalysts suffer from the outer cell membrane acting as a diffusion barrier for the highly hydrophobic substrate/product, while the use of purified enzymes leads to dramatic loss of stability. Here we present an unexplored strategy for biocatalysis: the application of squalene-hopene-cyclase spheroplasts. By removing the outer cell membrane, we produce stable and substrate-accessible biocatalysts. These spheroplasts exhibit up to 100-fold higher activity than their whole-cell counterparts for the biotransformations of squalene, geranyl acetone, farnesol, and farnesyl acetone. Their catalytic ability is also higher than the purified enzyme for all high molecular weight terpenes. In addition, we introduce a concept for the carrier-free immobilization of spheroplasts via crosslinking, crosslinked spheroplasts. The crosslinked spheroplasts maintain the same catalytic activity of the spheroplasts, offering additional advantages such as recycling and reuse. These timely solutions contribute not only to harness the catalytic potential of the squalene-hopene cyclases, but also to make biocatalytic processes even greener and more cost-efficient.

Automated summary

The researchers have found that spheroplasts of squalene-hopene cyclase, obtained by removing the outer cell membrane, exhibit higher catalytic activity compared to the enzymes and whole cells. They also introduce a concept of crosslinking the spheroplasts for recycling and reuse. These findings provide a potential solution for the production of bioactive compounds in a sustainable and cost-efficient manner.