Immobilization of an integral membrane protein for biotechnological phenylacetaldehyde production

• The production of SOI from a Rhodococcus strain was optimized.
• We could covalently immobilize the membrane-embedded SOI on SBA-15 silica carriers.
• Linkage of SOI to the carriers improved its stability toward organic phases.
• For the first time, we applied a non-toxic flexibilizer as an organic phase.
• The SBA-15-bound SOI in a two-phase system yielded 1.6–2.0× higher product amounts.

Styrene oxide isomerase (SOI) has previously been shown to be an integral membrane protein performing a highly selective, hydrolytic ring opening reaction of epoxides to yield pure aldehydes. Earlier studies had also shown a high sensitivity of SOIs toward their product phenylacetaldehyde which caused an irreversible inhibition and finally complete loss of activity at higher aldehyde concentrations. Here we report on the covalent immobilization of a styrene oxide isomerase (SOI) on SBA-15 silica carriers. The production of the SOI from a Rhodococcus strain was optimized, the enzyme was enriched and immobilized, and finally the biocatalyst was applied in aqueous as well as in two-phase systems. Linkage of the protein to epoxide or amino groups on the SBA-based carriers led to relatively poor stabilization of the enzyme in an aqueous system. But, improved stability was observed toward organic phases like the non-toxic phthalate-related 1,2-cyclohexane dicarboxylic acid diisononyl ester (Hexamol DINCH) which here to our knowledge was used for the first time in a biotechnological application. With this two-phase system and the immobilized SOI, 1.6–2.0× higher product yields were reached and the lifetime of the biocatalyst was tremendously increased.