Organization of the Mal operon (A) and the modular structure of SpuA (B). Large arrows represent genes and their direction of transcription in the Mal operon (B). Small arrows indicate the promoters and their directionality. The modules of SpuA are labelled indicating unknown modules (UNK), the family 41 carbohydrate-binding modules (CBM41-1 and CBM41-2), a linker module, and the N-, C-, and (α/β)8-barrel of the catalytic domain. The construct used for the work in this study is shown immediately below the full-length schematic.