β-Glucan (Yeast; Alkali Soluble)

Plant cell walls are highly dynamic structures that are composed predominately of polysaccharides. As such, endogenous carbohydrate active enzymes (CAZymes) are central to the synthesis and subsequent modification of plant cells during morphogenesis. The endo-glucanase 16 (EG16) members constitute a distinct group of plant CAZymes, angiosperm orthologs of which were recently shown to have dual β-glucan/xyloglucan hydrolase activity. Molecular phylogeny indicates that EG16 members comprise a sister clade with a deep evolutionary relationship to the widely studied apoplastic xyloglucan endo-transglycosylases/hydrolases (XTH). A cross-genome survey indicated that EG16 members occur as a single ortholog across species and are widespread in early diverging plants, including the non-vascular bryophytes, for which functional data were previously lacking. Remarkably, enzymological characterization of an EG16 ortholog from the model moss Physcomitrella patens (PpEG16) revealed that EG16 activity and sequence/structure are highly conserved across 500 million years of plant evolution, vis-à-vis orthologs from grapevine and poplar. Ex vivo biomechanical assays demonstrated that the application of EG16 gene products caused abrupt breakage of etiolated hypocotyls rather than slow extension, thereby indicating a mode-of-action distinct from endogenous expansins and microbial endo-glucanases. The biochemical data presented here will inform future genomic, genetic, and physiological studies of EG16 enzymes.

The fungal cell wall is the first point of contact between fungal pathogens and host organisms. It serves as a protective barrier against biotic and abiotic stresses and as a signal to the host that a fungal pathogen is present. The fungal cell wall is made predominantly of carbohydrates and glycoproteins, many of which serve as binding receptors for host defence molecules or activate host immune responses through interactions with membrane-bound receptors. Plant defensins are a large family of cationic antifungal peptides that protect plants against fungal disease. Binding of the plant defensin NaD1 to the fungal cell wall has been described but the specific component of the cell wall with which this interaction occurred was unknown. The effect of binding was also unclear, that is whether the plant defensin used fungal cell wall components as a recognition motif for the plant to identify potential pathogens or if the cell wall acted to protect the fungus against the defensin. Here we describe the interaction between the fungal cell wall polysaccharides chitin and β-glucan with NaD1 and other plant defensins. We discovered that the β-glucan layer protects the fungus against plant defensins and the loss of activity experienced by many cationic antifungal peptides at elevated salt concentrations is due to sequestration by fungal cell wall polysaccharides. This has limited the development of cationic antifungal peptides for the treatment of systemic fungal diseases in humans as the level of salt in serum is enough to inactivate most cationic peptides.

The purpose of this study was to investigate and compare adjuvant effects of soluble β-glucans from barley and Saccharomyches cerevisia in induction of antigen specific humoral immune responses. Mice were immunized with conalbumin at a relatively low concentration in the presence of beta glucans. Anti-conalbumin antibodies in the sera of immunized and control mice were quantified by ELISA. At high doses, both of glucans increased effectively levels of circulating IgM and IgG antibodies which were specific for conalbumin. However, coadministration of glucan from barley at 1 μg dose resulted in lower yield in IgG1, IgG2a, IgG2b, and IgA levels in comparison to that of yeast-derived glucan at the same dose. We also found that antigen (conalbumin) specific antibody levels enhanced by β-glucan from Saccharomyches cerevisia were always higher than those of the glucan from barley. Based on these findings, we concluded that (1,3),(1,6)-β-D-glucan from yeast cell wall might have superior immunostimulant activity in induction of antigen specific humoral immune responses over (1,3),(1,4)-β-D-glucan from barley.