Carbohydrate Binding Module family 36 (CBM36); appended mainly to glycoside hydrolase family 11 (GH11) domains; xylan binding
This family includes carbohydrate binding module family 36 (CBM36) most of which appear appended to glycoside hydrolase family 11 (GH11) domains. These CBMs are non-catalytic carbohydrate binding domains that facilitate the strong binding of the GH11 catalytic modules with their dedicated, insoluble substrates. GH11 domains have xylanase (endo-1,4-beta-xylanase) activity which catalyzes the hydrolysis of beta-1,4 bonds of xylan, the major component of hemicelluloses, to generate xylooligosaccharides and xylose. This family includes XynB from Dictyoglomus thermophilum Rt46B.1 and Xyn11A from Pseudobutyrivibrio xylanivorans Mz5T. Xyn11A is a multicatalytic enzyme with an N-terminal GH11 domain, a CBM36 domain, and a C-terminal putative NodB-like polysaccharide deacetylase which is predicted to be an acetyl esterase involved in debranching activity in the xylan backbone. CBM6 is an unusual CBM as it represents a chimera of two distinct binding sites with different modes of binding: binding site I within the loop regions and binding site II on the concave face of the beta-sandwich fold. Consistent with its structural and sequence similarity to CBM6, CBM36 binds xylan, but only at binding site I, and in a calcium-dependent manner; the latter suggests its potential application in affinity labeling.
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