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An alternative strategy for structural glucanomics using β-gluco-oligosaccharides from the brown algae Ecklonia stolonifera as models
- Sumiyoshi, Wataru, Miyanishi, Nobumitsu, Nakakita, Shin-ichi, Tsutsui, Shoko, Yamada, Keita, Nakakita, Yukari, Yoshioka, Shin, Asao, Masakatsu, Hirabayashi, Jun
- Bioactive carbohydrates and dietary fibre 2015 v.5 no.2 pp. 137-145
- Ecklonia, acid hydrolysis, beta-glucans, dietary fiber, digestion, fluorescence, gel chromatography, models, oligosaccharides
- 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 (<4000Da, 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.