Activity of squalene-hopene cyclases in bicontinuous microemulsions

• AacSHC is active in bicontinuous microemulsions despite the presence of organic solvents.
• AacSHC has a significantly enhanced selectivity in bicontinuous microemulsions.
• AacSHC does not change its conformation in an environment containing surfactant and organic solvent.

The paper at hand deals with biocatalysis in bicontinuous microemulsions. The latter consist of a dynamic network of oil and water domains separated by a monolayer of surfactant molecules, i.e. the interfacial layer. A microemulsion with the composition buffer – n-octane – nonionic surfactant was tested as reaction medium for an enzyme-catalysed reaction with a focus on the conversion of hydrophobic substrates, which are difficult to convert in aqueous buffer solutions. For the study at hand, we chose to investigate the activity of the squalene-hopene cyclase from Alicyclobacillus acidocaldarius (AacSHC) towards its natural substrate squalene in bicontinuous microemulsions. Firstly, the study revealed that the activity of AacSHC depends linearly on the enzyme concentration. Secondly, a hyperbolic curve was found for the dependence of the activity on the substrate concentration and a saturation of the AacSHC at substrate concentrations above 20 mM was observed. Thirdly, the composition of the interfacial layer was found to have no significant influence on the activity or on the conformation of AacSHC. Surprisingly and unexpectedly, a distinctly enhanced selectivity towards hopene was discovered in the microemulsion. To conclude, bicontinuous microemulsions were found to be a suitable reaction medium for biocatalytic reactions with the enzyme AacSHC.

Squalene-hopene cyclases from Alicyclobacillus acidocaldarius (AacSHC) in a bicontinuous microemulsion can convert the substrate either in the aqueous phase if small amounts of substrate are present (left) or at the interfacial layer if a contact between both is enabled (right).Figure optionsDownload as PowerPoint slide