Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2014
Publication Date: 8/19/2014
Publication URL: http://handle.nal.usda.gov/10113/60434
Citation: Bowman, M.J., Dien, B.S., Vermillion, K., Mertens, J.A. 2014. Structural characterization of (1-2)-ß-xylose-(1-3)-alpha-arabinose-containing oligosaccharide products of extracted switchgrass (Panicum virgatum, L.) xylan after exhaustive enzymatic treatment with alpha-arabinofuranosidase and ß-endo-xylanase. Carbohydrate Research. 398:63-71.
Interpretive Summary: Switchgrass is a perennial grass presently used as for forage and being developed as a bioenergy crop for conversion to biofuels. Up to 40% of switchgrass cell wall associated carbohydrates are xylan. Switchgrass xylan structural features were identified in three cultivars that have not been previously reported. These structures are not readily hydrolyzed by enzymes implying that this chemical bond may be partially responsible for xylan recalcitrance. Identification of the presence of this variation is relevant to commercial enzyme producers for designing improved enzymatic combinations to more effectively hydrolyze xylan to improve bioconversion yields.
Technical Abstract: Switchgrass (Panicum virgatum, L.) is a potential dedicated biomass crop for use in biocatalytic conversion systems to biofuels. Nearly 30% of switchgrass cell wall material is xylan. The complete depolymerization of xylan is desirable both as an additional carbon source for microbial fermentation and to reduce inhibitory effects xylooligomers may have on cellulolytic glycoside hydrolase enzymes. To identify structural features of switchgrass xylan that are not distinguishable by mass spectrometry alone, a alpha-arabinofuranosidase enzyme was used to remove the arabinose side-chains from alkali-extracted switchgrass xylan from three cultivars with simultaneous hydrolysis by beta-endo-xylanase to enrich for oligosaccharide products with extended branching. The two most abundant enzymatic digestion products were separated and characterized by LC-MSn, linkage analysis, and NMR. These two oligosaccharides were present in all three switchgrass cultivars and found to contain (1'2)-beta-xylose-(1'3)-alpha-arabinose side chains, a linkage not previously reported in switchgrass.