Modulation of cellulase activity by charged lipid bilayers with different acyl chain properties for efficient hydrolysis of ionic liquid-pretreated cellulose

摘要

The stability of cellulase activity in the presence of ionic liquids (ILs) is critical for the enzymatic hydrolysis of insoluble cellulose pretreated with ILs. In this work, cellulase was incorporated in the liposomes composed of negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) and zwitterionic phosphatidyicholines (PCs) with different length and degree of unsaturation of the acyl chains. The liposomal cellulase-catalyzed reaction was performed at 45 degrees C in the acetate buffer solution (pH 4.8) with 2.0 g/L CC31 as cellulosic substrate. The crystallinity of CC31 was reduced by treating with 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) at 120 degrees C for 30 min. The liposomal cellulase continuously catalyzed hydrolysis of the pretreated CC31 for 48 h producing glucose in the presence of 15 wt% [Bmim]Cl. The charged lipid membranes were interactive with [Bmim](+), as elucidated by the [Bmim]Cl-induced alterations in fluorescence polarization of the membrane-embedded 1,6-diphenyl-1,3,5-hexatriene (DPH) molecules. The charged membranes offered the microenvironment where inhibitory effects of [Bmim]Cl on the cellulase activity was relieved. The maximum glucose productivity G(p) of 10.8 mmol-glucose/(h mol-lipid) was obtained at the reaction time of 48 h with the cellulase incorporated in the liposomes = 5.0 mM) composed of 50 mol% POPG and 1,2-dilauroyl-sn-glycero-3-phosohocholine (DLPC) with relatively short and saturated acyl chains. (C) 2016 Elsevier B.V. All rights reserved.