Oleate hydratases open a biocatalytic access to hydroxy fatty acids by hydration of unsaturated fatty acids. Their practical applicability, however, is hampered by their low stability. In this study we report the immobilization of the oleate hydratase from Rhodococcus erythropolis PR4 on functionalized porous, spherical polymer beads. Different carrier materials promoting covalent, hydrophobic, ionic and his-tag affinity were screened and immobilization yields typically >95 % were observed. The highest activity recovery of 32 % was achieved by immobilization via ionic interaction with quaternary ammonium functionalized beads. Biochemical properties of the enzyme immobilized via ionic interaction remain unchanged upon immobilization. The immobilized enzyme was applied for synthesis of 10-hydroxystearic acid remaining stable under process conditions. Conversion of up to 100 mM oleic acid gave 10-hydroxystearic acid achieving a TON of up to 19,000. Successful recycling of the biocatalyst for up to ten cycles further demonstrate its potential for the synthesis of 10-hydroxystearic acid.

Astonishing progress has been achieved in unlocking new-to-nature biocatalysis in the past decades. The progress in protein engineering enabled research to efficiently incorporate artificial structural elements into enzyme design. Recent trends include cofactor mimetics, artificial metalloenzymes and non-canonical amino acids. In this perspective article, we present the state-of-the-art, discuss recent examples and our view on what we call artificial biocatalysis. Although these artificial systems undoubtedly increase the scope of biocatalysis, their applicability remains challenging. Fundamental questions regarding the impact of this research field are addressed in this perspective.