Enzymatic conversion of xylan into valuable products.
Xylan is the second most abundant plant polysaccharide in nature, composed of a highly diverse group of plant biopolymers where the xylan backbone is variable, branched and decorated with a number of carbohydrates including uronic acid, arabinose, and other compounds. This considerable chemical and structural variability interferes with efficient utilization. This Forest Service research focuses on identifying and characterizing enzymes specific to these various compositions and conformations to build an enzyme biocatalyst tool-set enabling specific conversion of xylan to desired materials for further use; for example, in the production of biofuels, green chemicals, and the conversion of xylans to designed oligoxylosides for use as nutraceuticals in diet supplementation as prebiotics. Such enzymes also can be used as animal feed amendments to increase the release of metabolizable sugars. The researchers take a bioinformatics approach leveraging the enormous amount of genomics information that has been collected to identify candidate enzymes by performing alignments and observing those that differ in regions believed to determine the catalytic specificity in known enzymes. Genes encoding candidate enzymes are then recovered using molecular genetics and constructs for expression are developed by rational design. Enzyme products expressed from these recombinant genes are then biochemically characterized against a variety of xylan and xylooligosaccharide substrates. Those with novel catalytic specificities are further defined by X-ray crystallography in order to determine the molecular features enabling the novel function. The researchers have identified glycosyl hydrolases whose activities are both dependent and independent of an uronic acid moiety, those showing a preference for arabinose decorated xylan, as well as enzymes that catalyze the specific removal of substitutions such as arabinose from the xylan backbone. Each of these contributes to a set of enzymes that will allow the realization of the considerable economic potential tied up in xylan.
Forest Service Partners