Functional analysis of α-1,3-glucanase domain structure from Streptomyces thermodiastaticus HF3-3.

α-1,3-Glucanase from Streptomyces thermodiastaticus HF3-3 (Agl-ST) has been classified in the glycoside hydrolase (GH) family 87. Agl-ST is a multi-modular domain consisting of an N-terminal β-sandwich domain (β-SW), a catalytic domain, an uncharacterized domain (UC), and a C-terminal discoidin domain (DS). Although Agl-ST did not hydrolyze α-1,4-glycosidic bonds, its amino acid sequence is more similar to GH87 mycodextranase than to α-1,3-glucanase. It might be categorized into a new subfamily of GH87. In this study, we investigated the function of the domains. Several fusion proteins of domains with green fluorescence protein (GFP) were constructed to clarify the function of each domain. The results showed that β-SW and DS domains played a role in binding α-1,3-glucan and enhancing the hydrolysis of α-1,3-glucan. The binding domains, β-SW and DS, also showed binding activity toward xylan, although it was lower than that for α-1,3-glucan. The combination of β-SW and DS domains demonstrated high binding and hydrolysis activities of Agl-ST toward α-1,3-glucan, whereas the catalytic domain showed only a catalytic function. The binding domains also achieved effective binding and hydrolysis of α-1,3-glucan in the cell wall complex of Schizophyllum commune.