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Carbohydrate Binding Module Family 89

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Ligand specificities

The CBM89 family was created based on the discovery of an N-terminal domain appended to a GH10 xylanase recovered from a metagenome-assembled genome (MAG) of the capybara gut microbiota. The founding member, CapCBM89, was shown to interact with beechwood xylan and rye arabinoxylan according to affinity gel electrophoresis (AGE) [1]. Although similar β-helix structural architectures have been found in the families GH28, GH91, PL6, and CE8, no catalytic activity of the isolated CapCBM89 was observed on the substrates tested [1].

Structural Features

Figure 1. CapCBM89 structure (PDB 7JVI [1]). The Ca2+ (orange sphere), its coordinating residue (D344) and the two residues that impaired polysaccharide binding (Y62 and E82) are highlighted.

The crystal structure of the founding member was solved at 1.85 Å resolution, which consists of 14 helical turns establishing a parallel β-helix fold [1]. A Ca2+ was found in the structure, connecting the 11th and 12th helical turns (PDB 7JVI). The role of the ion seems to be only related to the domain stabilization, since a mutation in the Ca2+ binding site (D344L) affected the protein stability but not its capacity to bind to arabinoxylan/xylan [1]. In CapCBM89, mutants Y62A and E82A impaired the capacity to bind to arabinoxylan/xylan, indicating the importance of this motif for carbohydrate binding [1] .


In general, CBM89 members comprise approximately 600 to 1000 residues, which can be fused to GH domains. The most common associated glycoside hydrolases are from the GH10 family. The founding member, CapCBM89, was found appended to the N-terminus of a GH10 domain, which is clustered with CAZymes targeting arabinoxylans [1]. This CAZyme cluster encodes the CapCBM89-GH10 and two exo-acting enzymes from GH43 and GH97 families [1]. The GH10 domain is active on arabinoxylan and xylan, which is in agreement with the binding assays of CapCBM89, suggesting that CapCBM89 targets the GH10 domain to these substrates for catalysis [1].

Family Firsts

First Identified
The first identified CBM89 member (CapCBM89) was from an uncultured Bacteroidaceae MAG57 recovered from the capybara gut microbiome [1] .
First Structural Characterization
The first CBM89 structure is PDB 7JVI, retrieved from the capybara gut microbiome [1] .


  1. Cabral L, Persinoti GF, Paixão DAA, Martins MP, Morais MAB, Chinaglia M, Domingues MN, Sforca ML, Pirolla RAS, Generoso WC, Santos CA, Maciel LF, Terrapon N, Lombard V, Henrissat B, and Murakami MT. (2022). Gut microbiome of the largest living rodent harbors unprecedented enzymatic systems to degrade plant polysaccharides. Nat Commun. 2022;13(1):629. DOI:10.1038/s41467-022-28310-y | PubMed ID:35110564 [Cabral2022]