HEMICELLULASES FOR MEDIATING BIOMASS SACCHARIFICATION

Authors: Jordan, Douglas; Li, Xin Liang; Dien, Bruce; Cotta, Michael

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/13/2006
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Glycosidic bonds are among the strongest chemical bonds that link monomeric residues of biopolymers, requiring large energy inputs to overcome activation-energy barriers for cleavage. Harnessing the catalytic power of glycoside hydrolases and auxiliary hydrolytic enzymes for saccharification of herbaceous biomass holds potential for lowering energy inputs tremendously. Additionally, enzymatic saccharification offers the potential advantage of providing monosaccharides in high yield, avoiding side products which occur in nonenzymatic processes that employ harsh chemical and physical treatments; not only are the side products wasteful by reducing yield, some (e.g., furans) poison subsequent fermentations. Thus, enzymes could provide cost-efficient avenues for supplying high quality feedstocks of monosaccharides for fermentation to fuel ethanol and other bioproducts. Much of the catalytic power of enzymes resides in the match between the enzyme active site and its substrate, necessitating recruitment of individual enzymes for each type of substrate. To this end, progress has been made in developing catalytically efficient and robust cellulases, glycoside hydrolases that act on bonds joining glucose residues in the varied forms of cellulose, the most abundant biopolymer. Hemicellulose (xylans), the second most abundant biopolymer, composes a significant portion of plant cell walls. Consequently, enzymatic saccharification of herbaceous biomass in high yield requires specific glycoside hydrolases and auxiliary enzymes that act upon hemicellulose to release constituent monosaccharides. Moreover, it has been found that complete hydrolysis of hemicellulose from herbaceous biomass leads to greater yield of glucose from cellulose by cellulase action. For these reasons, our laboratories have focused on identification of catalytically efficient and robust enzymes that act on hemicellulose. This presentation will review our progress in discovery of hemicellulases and their suitability for saccharification of biomass. One example, from our laboratories, is the discovery of a catalytically efficient beta-D-xylosidase that has associated alpha-L-arabinofuranosidase activity. A second example, from our laboratories, is the induction of glycoside hydrolases and auxiliary enzymes in two fungal species, which are effective in saccharifying biomass when used in combination.