Function of a laminin_G_3 module as a carbohydrate‐binding module in an arabinofuranosidase from Ruminiclostridium josui

Laminin_G_3 modules can exist together with family‐43 catalytic modules of glycoside hydrolase ( GH 43), but their functions are unknown. Here, a laminin_G_3 module and a GH 43 module derived from a Ruminiclostridium josui modular arabinofuranosidase Abf43A‐Abf43B‐Abf43C were produced individually as Rj LG 3 and Rj GH 43_22, respectively, or combined as Rj GH 43‐1 to gain insights into their activities. Isothermal calorimetry analysis showed that Rj LG 3 has high affinity toward 3 2 ‐α‐ l ‐arabinofuranosyl‐(1,5)‐α‐ l ‐arabinotriose but not for α‐1,5‐linked arabinooligosaccharides, which suggests that Rj LG 3 interacts specifically with a branched arabinofuranosyl residue of an arabinooligosaccharide but not an arabinofuranosyl residue at the end of α‐1,5‐linked arabinooligosaccharides. Rj GH 43‐1 (with CBM ) shows higher activity toward sugar beet arabinan than Rj GH 43_22 (without CBM ), which suggests that the LG 3 module in Rj GH 43‐1 plays an important role in substrate hydrolysis as a carbohydrate‐binding module.