Feruloylation in Grasses： Current and Future Perspectives

In the cell walls of forage grasses, ferulic acid is esterified to arabinoxylans and participates with lignin monomers in oxidative coupling pathways to generate ferulate-polysaccharide-lignin complexes that cross-link the cell wall. The accumulation of ferulates and the cross-linking of arabinoxylans via diferulate esters are hypothesized to function in various processes in plants. The specific roles of arabinoxylan feruloylation as well as the nature, cellular localization, and substrate for arabinoxylans feruloylation of cell walls are reviewed. The various approaches that have been used for assessing the specific roles of feruloylation are described and assessed. I argue that, until recently, the specific role of feruloylation in these various processes has been established largely by indirect experiments and, although these studies reached similar conclusions about the potential importance of wall feruloylation, they suffer from a common problem： namely they depend on correlations between two processes and do not stem from a detailed understanding of the mechanisms of feruloylation. I also argue that the nature of arabinoxylan feruloylation remains uncertain.

Combinatorial Enzyme Approach for Production and Screening of Libraries of Feruloyl Oligosaccharides

Combinatorial chemistry involves the chemical or biological synthesis of diverse variation of the structures of a target molecule and the library is then screened for variants of desirable target properties. The approach has been a focus of research activity in drug discovery and biotechnology. This report is to demonstrate the application of enzyme technology using the concept of combinatorial chemistry as a novel approach for the bioconversion of plant fibers. Wheat insoluble fiber was subjected to combinatorial enzyme digestion to create structural variants of feruloyl oligosaccharides (FOS). Fractionation and screening resulted in the isolation of a fraction of bioactive FOS species showing antimicrobial activity. These results demonstrate the feasibility and usefulness of the combinatorial enzyme technique in the transformation of plant biomass to value-added products.

Breakdown of Corn Fiber by a Metagenomic Ferulolyl Esterase in Combination with Glycosyl Hydrolases

A feruloyl esterase (FAE-C6) gene of 957 bp was isolated from rumen microbial metagenome, subcloned into pET32b vector, and expressed in Escherichia coli. The enzyme purified in active form, consisted of 319 amino acid residues, with a molecular weight of 43.7 based on SDS-PAGE. Homology modeling showed that the FAE contained the catalytic triad composed of Ser154-Asp263His295 and a classical Gly-X-Ser154-X-Gly nucleophile motif commonly found in esterases. The FAE-C6 was characterized using corn fiber as substrate. Its combining action with glycoside hydrolases (C, X, A) individually and in various combinations was studied with focus on the difference in the effects on FA and sugar release. Glycoside hydrolases with endo-xylanase included in the enzyme mixture showed significant impact on increasing the FA yield. For the release of sugar, FAE enhanced the yield in all hydrolase combinations moderately and endo-xylanase was not the key factor in the enzyme formulation.