17-18: The “hydrolytic boosting effect” of GH61 addition is heavily influenced by the ease of accessibility and the nature of the cellulosic substrate

The development of a renewable, biomass based, fuels and chemicals “Biorefinery” process will be crucial if we are to transition to a more environmentally friendly economy. However, the limited efficacy of “cellulase mixtures” to breakdown the polysaccharides within lignocellulose into sugar platform is still a bottleneck! Although the catalytic activities of cellulases on soluble substrates are comparable with other polysaccharides, such as amylases when hydrolysing starch, the hydrolytic potential of cellulase enzymes towards pretreated lignocellulosic substrates is dramatically lower. This is primarily due to the limited accessibility of the enzymes to most of the glycosidic bonds. We and other workers have shown that accessory enzymes can increase cellulose accessibility and significantly enhance the hydrolytic potential of cellulases. One of these accessory enzymes, GH61, has been shown to enhance cellulose accessibility by cleavage of the highly ordered cellulose via a redox reaction. While progress has been made in better defining GH61’s protein structure and catalytic mechanism, the dynamics/synergies of this enzyme when it acts cooperatively with a “cellulase mixture” during hydrolysis of  “realistic”, industrially relevant pretreated lignocellulosic substrates, it is still not completely understood. The presentation will describe the synergistic cooperation between GH61 and cellulases during the hydrolysis of model and pretreated substrates and the influence that the physicochemical characteristics of these substrates has on the ability of GH61 to enhance the hydrolytic potential of the cellulase mixture. It was apparent that the “boosting effect” resulting from GH61 addition is less influential on highly accessible cellulose.