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 (GH43), but their functions are unknown. Here, a laminin_G_3 module and a GH43 module derived from a Ruminiclostridium josui modular arabinofuranosidase Abf43A-Abf43B-Abf43C were produced individually as RjLG3 and RjGH43_22, respectively, or combined as RjGH43-1 to gain insights into their activities. Isothermal calorimetry analysis showed that RjLG3 has high affinity toward 3 -α-l-arabinofuranosyl-(1,5)-α-l-arabinotriose but not for α-1,5-linked arabinooligosaccharides, which suggests that RjLG3 interacts specifically with a branched arabinofuranosyl residue of an arabinooligosaccharide but not an arabinofuranosyl residue at the end of α-1,5-linked arabinooligosaccharides. RjGH43-1 (with CBM) shows higher activity toward sugar beet arabinan than RjGH43_22 (without CBM), which suggests that the LG3 module in RjGH43-1 plays an important role in substrate hydrolysis as a carbohydrate-binding module.