High hydrolytic activity of the metagenomic lipase LipC12 in deep eutectic solvents

Deep eutectic solvents (DESs) have been shown to increase the activity of lipases in biocatalytic processes, especially when added at intermediate concentrations. We evaluated the effect of DESs on the hydrolysis of pnitrophenyl palmitate (p-NPP) by a metagenomic lipase, LipC12. The hydrogen bond acceptor was choline chloride (ChCl), while sorbitol (Sor), xylitol (Xyl), Glycerol (Gly), ethylene glycol (EG), triethylene glycol (TEG) and urea (U) were tested as hydrogen bond donors. The best results were obtained at 25% (v v-1) DES, with the increases in hydrolytic activity, compared to activity in buffer, being 18-fold for ChCl:Sor (2:1), and 10- to 12fold for ChCl:Gly (1:2), ChCl:EG (1:2) and ChCl:Xyl (2:1). Dynamic Light Scattering analysis suggests that protein disaggregation played a key role in this activation: the hydrodynamic radius of LipC12 was 157 nm in buffer, but ranged from about 1 to 7 nm in DESs at different concentrations. The addition of 100 mM NaCl to the DEScontaining media (at 25% v v-1 DES) slightly improved LipC12 activity. Addition of the hydrogen-bond donor alone also increased the p-NPP hydrolyzing activity with 30% (w v-1) sorbitol or xylitol giving 4.5-fold higher activities, compared to activity in buffer. Our fold-improvements in activity are the highest yet reported for the pNPP-hydrolyzing activity of lipases and suggest that more studies are required, especially with other biocatalytic reactions such as esterification and transesterification.