Carrier immobilization and auto-exposition favoring reuse of silyletherase SilE-R from Brassica sp. with high activity and enantiospecificity.

Objectives: Investigation of immobilization methods promoting the use of silyletherases from Brassica sp. for the efficient and enantiospecific hydrolysis of silyl-protected hydroxyl functions.

Results: Different supports for adsorptive and covalent binding of the silyletherase SilE-R as well as exposure of the enzyme on the surface of Bacillus subtilis endospores, so-called SporoBeads, were evaluated. While the highest protein loading of 26 mg enzyme per gram was obtained by adsorptive binding, the best combination of specific activity and enantiospecificity was obtained when SilE-R was exposed on SporoBeads. Protein loading was estimated at 2.6 mg per gram of spore, which was in the same range as after covalent binding to a carrier. In six repeated reaction cycles, SporoBeads exposing SilE-R lost less than 10% of their catalytic activity. The enantiomeric excess could not be increased even with short reaction times, but remained constant over all repeated cycles.

Conclusion: The exposure of silyletherases on SporoBeads has been identified as a promising approach for the synthetic application of this novel type of enzyme, although some properties relevant for catalytic applications need to be further improved.