Carbohydrate Binding Module Family 91

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• Author: Daichi Ito
• Responsible Curator: Elizabeth Ficko-Blean

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CAZy DB link

http://www.cazy.org/CBM91.html

Ligand specificities

CBM91 from Paenibacillus xynaniclasticus bound to oat spelt xylan with K_a value of 2.0×10^-5 M^-1, and bound birchwood xylan. But it did not bind to cellulosic substrates (carboxymethyl-cellulose, ball-milled cellulose and lichnan). Therefore, CBM91 can recognize and bind to insoluble xylan [1].

Structural Features

Figure 1. The structure of PxXyl43A and CBM91. The prediction structure by Alpha Fold 2 of CBM91(red). This CBM91 is appended to the catalytic domain of PxXyl43A(green).

Alpha Fold 2 structure analysis of PxCBM91 exhibited a β-sandwich fold consisted of 12 β-strands and two opposing antiparallel beta sheets[2]. The concave surface and loops around it connecting the β-strands possesse several hydrophobic amino acid residues, the surface is expected to be the binding site.

Functionalities

CBM91 often is connected to the β-xylosidases belonging to glycoside hydrolase family 43 ([GH43]). CBM91 binds to the substrates and would place the catalytic domain in the vicinity of substrates in which substrate concentration is high. These enzymes would utilize CBM91 as a tool for efficient saccharification in combination with other xylanases which release xylobiose and/or xylo-oligosaccharides from insoluble substrates. Paenibacillus xylaniclastuicus was isolated from anaerobic digester fed with pineapple waste and grows with xylose as sole carbon source. Xylosidases, like GH43, which produce xylose from xylan and xylooligosaccharides and connects to CBM91 is one of vial enzymes. Therefore, CM91 would contribute to produce the carbon sources for the growth of xylolytic bacteria.

Family Firsts

First Identified

PxCBM91 from PxXyl43A of Paenibacillus xynaniclasticus strain TW1 [1].

First Structural Characterization

β-D-xylosidase, a family 43 glycoside hydrolase from Clostridium acetobutylicum ATCC 824 PDB ID 1Y7B.

References

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 |

2. Ito, D., 2023. Characterization of plant cell wall degrading enzymes from Paenibacillus sp. Ph. D. Mie University.