Abstract
BackgroundThe conversion of plant biomass to ethanol via enzymatic cellulose hydrolysis offers a potentially sustainable route to biofuel production. However, the inhibition of enzymatic activity in pretreated biomass by lignin severely limits the efficiency of this process.ResultsBy performing atomic-detail molecular dynamics simulation of a biomass model containing cellulose, lignin, and cellulases (TrCel7A), we elucidate detailed lignin inhibition mechanisms. We find that lignin binds preferentially both to the elements of cellulose to which the cellulases also preferentially bind (the hydrophobic faces) and also to the specific residues on the cellulose-binding module of the cellulase that are critical for cellulose binding of TrCel7A (Y466, Y492, and Y493).Conclusions Lignin thus binds exactly where for industrial purposes it is least desired, providing a simple explanation of why hydrolysis yields increase with lignin removal.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0379-8) contains supplementary material, which is available to authorized users.
Highlights
The conversion of plant biomass to ethanol via enzymatic cellulose hydrolysis offers a potentially sustainable route to biofuel production
The simulation investigates the binding of Cel7A to cellulose prior to the enzyme hydrolyzing a glucan chain, and how this binding is affected by the presence of lignin
In the starting structure of the system, i.e., prior to the simulation (Fig. 1), no enzymes are bound to the biomass, but there is extensive cellulose–lignin association derived from previous simulations of pretreated biomass [40] which remained virtually unchanged after the addition of the enzymes in the current study
Summary
The conversion of plant biomass to ethanol via enzymatic cellulose hydrolysis offers a potentially sustainable route to biofuel production. The inhibition of enzymatic activity in pretreated biomass by lignin severely limits the efficiency of this process. A significant barrier to cost-effective cellulosic biofuel production is the current inefficient hydrolysis of cellulose glycosidic bonds to fermentable sugars by cellulase enzymes [2,3,4]. Various lignin-related inhibitory processes have been proposed, including cellulose association with lignin, blocking enzymatic access to cellulose [15,16,17,18], and the unproductive binding of the enzymes to lignin [19,20,21,22,23]. An atomic-detailed characterization of how cellulases become inhibited by lignin is currently lacking
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