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Carbohydrate Binding Module Family 91

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This page is currently under construction. This means that the Responsible Curator has deemed that the page's content is not quite up to CAZypedia's standards for full public consumption. All information should be considered to be under revision and may be subject to major changes.

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Ligand specificities

CBM91 bind oat spelt xylan with Ka value of 2.0×10-5 M-1, and can bind birchwood xylan. But it does not bind to cellulosic substrates, carboxymethyl-cellulose, ball-milled cellulose and lichnan. So, CBM91 can recognize and bind to insoluble xylan [1].

Structural Features

Figure. The structure of CBM91. The prediction structure by Alpha Fold 2 of CBM91(red). This CBM91 is appended to the catalytic domain of PxXyl43A(green).
  • Fold: β-sandwich
  • Type: Type B


CBM91 often is found in the β-xylosidases, for example GH43. These seem not to need CBMs because the substrates, xylobiose and/or xylo-oligosaccharides, are soluble. So, it is likely that the binding ability may not be involved in β-xylosidase activity of catalytic domain. β-xylosidases would utilize CBM91 as a tool for efficient saccharification by combination with other enzymes and xylanases which release xylobiose and/or xylo-oligosaccharides from insoluble substrates. CBM91 binds to the substrates and would places the catalytic domain at the vicinity of substrates in which substrate concentration is high.

Family Firsts

First Identified
CBM91 from Paenibacillus xynaniclasticus strain TW1 [1].
First Structural Characterization
β-D-xylosidase, a family 43 glycoside hydrolase from Clostridium acetobutylicum ATCC 824 PDB ID 1Y7B.


  1. Ito D, Nakano E, Karita S, Umekawa M, Ratanakhanokchai K, and Tachaapaikoon C. (2022). Characterization of a GH Family 43 β-Xylosidase Having a Novel Carbohydrate-binding Module from Paenibacillus xylaniclasticus Strain TW1. J Appl Glycosci (1999). 2022;69(3):65-71. DOI:10.5458/jag.jag.JAG-2022_0001 | PubMed ID:36312872 [Ito2022]