Tuesday, April 20, 2010
11-66

Synthetic enzyme mixtures for biomass conversion: The 'core set'

Goutami Banerjee, Suzana Car, John S. Scott-Craig, Melissa Borrusch, Nigat Aslam, and Jonathan D. Walton. Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824

Enzymes for releasing fermentable sugars from biomass feedstocks are one of the major costs in cellulosic ethanol production. Commercially available enzyme cocktails for conversion of plant biomass are complex mixtures of poorly defined activities and suboptimal ratios. The goal of this project is to rationalize enzyme mixtures by constructing defined mixtures for different  pretreatment/biomass combinations. Toward this goal, the first step is to define a ‘minimal enzyme set’ that is capable of releasing at least some significant amount of glucose and xylose from corn stover. The second phase involves the sequential and systematic addition of ‘accessory proteins’ to the minimal enzyme set. This serves to identify additive and synergistic proteins (see companion poster by Scott-Craig et al.). Our core set includes one endo-glucanase (EG1), two cellobiohydrolases (CBH1 and CBH2), β-glucosidase (BG), β-xylosidase (BX), and an endo-xylanase (XYN3). Mixtures of pure, single core enzymes were designed and analyzed statistically to obtain an optimal ratio for maximum glucan and xylan conversion. The resulting optimized ‘core set’ provided a starting point for the testing and optimization of additional ‘accessory enzymes’ for development of mixtures of higher specific activities.