Understanding the Structure and Function of Enzymes in ILs for Improved Biocatalysis

Evaluating the degree to which an enzyme is able to maintain its structure and function in non-native solvents has widespread relevance, particularly to the field of biocatalysis. Ionic liquids (ILs) represent one such category of non-native solvents that have been gaining ground in recent decades as important solvents for biocatalysis, due to their low flammabilities and vapor pressures and highly tunable solvent properties. The discovery that some enzymes are able to maintain a level of function/activity in ILs has led to large-scale interest in determining the extent of the broadened landscape of viable biotransformations. Despite this interest, however, progress has been hindered due to a lack of a molecularly detailed understanding of how to rationally design enzymes to have increased stability in ILs. Molecular simulation has proven to be an invaluable tool at providing insight into the atomic level interactions of enzymes with ILs. Included in this poster are results from molecular dynamics (MD) simulations of multiple different enzyme/IL systems of interest: (1) a newly discovered family of enzymes called lytic polysaccharide monooxygenases (LPMOs) are simulated in three aqueous ILs at 0, 10, and 20 weight percent to evaluate their potential to aid cellulases in the decomposition of cellulose for conversion into fuels and chemicals, and (2) Bacillus subtilis lipase A is simulated in aqueous [BMIM][Cl] at 0, 5, 10, and 20 volume percent to evaluate its potential to maintain stability and activity in ILs for general biocatalysis applications. Structural and dynamic analyses indicate LPMO enzymes are predicted to be highly stable across the range of IL solutions tested; however, key areas that deviated from the crystal structures are identified as a basis for future rational design efforts to increase stability in ILs through surface charge modifications. Additionally, preferred binding sites for IL ions on the surface of lipase A are identified and compared to experimental crystallographic data¹ as a means to stabilize against IL-induced inactivation.

References

[1] Nordwald, E.; Plaks, J.; Snell, J.; Sousa, M.; Kaar, J. Crystallographic Investigation of Imidazolium Ionic Liquid Effects on Enzyme Structure. Chembiochem 2015, 16, 2456-2459.