An alternative strategy for structural glucanomics using β-gluco-oligosaccharides from the brown algae Ecklonia stolonifera as models

Studies of β-glucans are often hampered by their structural diversity and complexity, which is problematic because interest in their effects on animal cells has increased in recent years. Herein, we present a comprehensive strategy for structural characterization of branched β-glucans, and as a proof-of-concept study, characterized laminarin and acid-soluble β-gluco-oligosaccharides (<4000 Da, void volume elute fraction of gel filtration on Bio-gel P-2) from the brown algae, Ecklonia stolonifera. The strategy involves quantitative fluorescence detection-high performance liquid chromatography that enables the characterization of di- and oligosaccharides after acid hydrolysis of the glucan. We found that laminarin is composed of β1-3 (72% in mol) and β1-6 (28%) anomeric bonds, whereas the E. stolonifera glucan is composed of β1-3 (57%) and β1-6 (43%) anomeric bonds. This composition is distinct from that of other brown algae β-glucans, for which the β1-6 bond content is much smaller. We also performed a detailed structural analysis of the 11 major β-gluco-oligosaccharides prepared by mild acid hydrolysis and β1-3-specific laminarinase digestion. All 11 oligosaccharides contained branches joined to the backbone by β1-6 bonds. Five of the oligosaccharides had extended branches; in this regard, the E. stolonifera glucan is unlike other characterized β-glucans. Our strategy should enable structural characterizations of β-branched glucans, for which no practical approach has been available until now.