Enzymes that catalyze cyclization of β-1,2-glucans.

β-1,2-Glucans are physiologically important polymers for interactions such as symbiosis and pathogenesis between organisms and adaptation to environmental changes. However, rarity of β-1,2-glucans in nature limits exploration of related enzymes. Recently, many β-1,2-glucan-degrading enzymes have been found after identification of a novel phosphorylase acting on β-1,2-glucooligosaccharides. The expansion of the repertoire has reached revelation of the cyclization mechanism of cyclic β-1,2-glucan synthase and led to finding of new enzymes catalyzing cyclization of β-1,2-glucans in a manner different from cyclic β-1,2-glucan synthase. In this review, we mainly focus on newly found enzymes that catalyze cyclization of β-1,2-glucans along with existence of β-1,2-glucan-associated carbohydrates in nature and introduction of the repertoire of β-1,2-glucan-degrading enzymes. KEY POINTS: • Newly found domain which cyclizes β-1,2-glucan created a new glycoside hydrolase family. • Cyclization is performed with a unique mechanism. • α-1,6-Cyclized β-1,2-glucan is produced by an enzyme in another newly found family.