Conjugation of Candida rugosa lipase with hydrophobic polymer improves esterification activity of vitamin E in nonaqueous solvent

We described a novel polymer-lipase conjugate for high-efficient esterification of vitamin E using vitamin E and succinic anhydride as the substrates in nonaqueous media. In this work, the monomer, N -isopropylacrylamide (NIPAM), was grafted onto Candida rugosa lipase (CRL) to synthesize poly(NIPAM) ( p NIPAM)-CRL conjugate by atom transfer radical polymerization via the initiator coupled on the surface of CRL. The result showed that the catalytic efficiencies of p NIPAM-CRL conjugates (19.5 – 30.3 L·s -1 ·mmol -1 ) were at least 7-times higher than that of free CRL (2.36 L·s -1 ·mmol -1 ) in DMSO. It was attributed to a significant increase in K cat of the conjugates in nonaqueous media. The synthesis catalyzed by p NIPAM-CRL conjugates was influenced by the length and density of the grafted polymer, water content, solvent polarity and molar ratio of the substrates. In the optimal synthesis, the reaction time was shortened at least 7-times, and yields of vitamin E succinate by p NIPAM- g -CRL and free CRL were obtained to be 75.4% and 10.1 % at 55°C after the reaction for 1.5 h. The result argued that conjugation with p NIPAM induced conformational change of the lid on CRL based on hydrophobic interaction, thus providing a higher possibility of catalysis-favorable conformation on CRL in nonaqueous media. Moreover, p NIPAM conjugation improved the thermal stability of CRL greatly, and the stability improved further with an increase of chain length of p NIPAM. At the optimal reaction conditions (55°C and 1.5 h), p NIPAM- g -CRL also exhibited good reusability in the enzymatic synthesis of vitamin E succinate and kept ∼ 70% of its catalytic activity after ten consecutive cycles. The research demonstrated that p NIPAM- g -CRL was a more competitive biocatalyst in the enzymatic synthesis of vitamin E succinate and exhibited good application potential under harsh industrial conditions.