CBM9_1 is a C-terminal domain on bacterial xylanase proteins, and it is tandemly repeated in a number of family-members. The CBM9 module binds to amorphous and crystalline cellulose and a range of soluble di- and monosaccharides as well as to cello- and xylo- oligomers of different degrees of polymerisation. Comparison of the glucose and cellobiose complexes during crystallisation reveals surprising differences in binding of these two substrates by CBM9-2. Cellobiose was found to bind in a distinct orientation from glucose, while still maintaining optimal stacking and electrostatic interactions with the reducing end sugar [1].

1: Crystal structures of the family 9 carbohydrate-binding module from Thermotoga maritima xylanase 10A in native and ligand-bound forms. Notenboom V, Boraston AB, Kilburn DG, Rose DR; Biochemistry. 2001;40:6248-6256. PMID:11371186