A starch-binding domain identified in α-amylase (AmyP) represents a new family of carbohydrate-binding modules that contribute to enzymatic hydrolysis of soluble starch

• A starch binding domain (SBD) was identified in the α-amylase (AmyP) of glycoside hydrolase subfamily GH13_37.
• SBD and its homologues form a novel carbohydrate-binding module family (CBM69).
• SBD provides new clues of biodiversity and evolution of SBD in the ocean.
• SBD exhibits a binding preference toward raw rice starch.
• SBD has a stronger effect on soluble starch hydrolysis than raw starch hydrolysis.

A novel starch-binding domain (SBD) that represents a new carbohydrate-binding module family (CBM69) was identified in the α-amylase (AmyP) of the recently established alpha-amylase subfamily GH13_37. The SBD and its homologues come mostly from marine bacteria, and phylogenetic analysis indicates that they are closely related to the CBM20 and CBM48 families. The SBD exhibited a binding preference toward raw rice starch, but the truncated mutant (AmyPΔSBD) still retained similar substrate preference. Kinetic analyses revealed that the SBD plays an important role in soluble starch hydrolysis because different catalytic efficiencies have been observed in AmyP and the AmyPΔSBD.