Type B CBM Function

As with Type A CBMs, the interactions of planar aromatic residues play a role in determining function, but in conjunction with other interactions, specifically hydrogen bonding. The aromatic interactions are often of the stacking type in which C-H bonds in electron-deficient systems interact with the cloud of 71 electrons of an (electron-rich) aromatic system the well-known 

Many isolated catalytic domains are less stable than the holoenzyme from which they are derived, and indeed CBM 22 was first identified as a thermo-stabilizing domain, rather than by its true function of enthalpy-driven binding of xylan and xylan oligosaccharides.  

The function of CBM Family 20 (sometimes called SBD, starch binding domains) is particularly well understood in the case where it is attached to a GH 15 catalytic module, as in the Aspergillus spp. glucoamylase. The SBD contains two saccharide binding sites, each of which relies on a Trp residue to interact with the hydrophobic portion of the amylose unit. Mutation of either Trp residue gives an enzyme which continues to bind to soluble starch, but no 

Although the p-sandwich fold is normally associated with binding of an extended chain, in at least one example, a CBM Family 6 with specificity for laminarin, the active site cleft is closed off so that the module is specific for the non-reducing end.  

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