Exploiting the Benefits of Homogeneous and Heterogeneous Biocatalysis: Tuning the Molecular Interaction of Enzymes with Solvents via Polymer Modification

The modification of enzymes with polymers holds tremendous promise as an approach to tune the molecular interactions of enzymes in diverse solvent environments. Here, we demonstrate the use of polymer modification to specifically modulate the thermoresponsive interactions of enzymes with non-native solvents. To demonstrate this approach, Bacillus subtilis lipase A (LipA) was modified with random copolymers of poly­(acryloylmorpholine-co-N-isopropyl acrylamide) (PAN). Modification of LipA with PAN permitted the reversible phase separation of LipA–PAN from 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]­[PF6]) in a temperature-dependent manner. By varying the compositions of the copolymer, the temperature dependence of this phase separation could be quantitatively controlled between 16 and 76 °C. Above the temperature of the phase transition, the enzyme was soluble in the ionic liquid (IL), resulting in enhanced transesterification activity (i.e., a 21-fold increase over unmodified LipA), whereas below the temperature of the phase transition, the enzyme could be readily separated and recycled. Remarkably, when recycled via sequential dissolution and precipitation as many as 10 times, the enzyme did not lose any activity. Using this approach, we also showed that the enzyme could be extracted into buffer as well as reversibly shuttled between buffer and the IL in response to changes in temperature. This approach ultimately permits the advantages of homogeneous and heterogeneous biocatalysis in non-native solvents to be exploited and may be readily extended to other enzymes, solvents, and external stimuli. Such an approach may further find application in other fields, including bioseparations, self-assembly, and drug delivery