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4  structures 718  species 2  interactions 803  sequences 12  architectures

Family: CHB_HEX (PF03173)

Summary: Putative carbohydrate binding domain

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This is the Wikipedia entry entitled "CHB HEX N-terminal domain". More...

CHB HEX N-terminal domain Edit Wikipedia article

CHB_HEX N-terminal domain
PDB 1c7t EBI.jpg
beta-n-acetylhexosaminidase mutant e540d complexed with di-n acetyl-d-glucosamine (chitobiase)
Symbol CHB_HEX
Pfam PF03173
Pfam clan CL0203
InterPro IPR004866
SCOP 1c7s

In molecular biology, the CHB HEX N-terminal domain represents the N-terminal domain in chitobiases and beta-hexosaminidases. Chitobiases degrade chitin, which forms the exoskeleton in insects and crustaceans, and which is one of the most abundant polysaccharides on earth.[1] Beta-hexosaminidases are composed of either a HexA/HexB heterodimer or a HexB homodimer, and can hydrolyse diverse substrates, including GM(2)-gangliosides; mutations in this enzyme are associated with Tay-Sachs disease.[2] HexB is structurally similar to chitobiase, consisting of a beta sandwich structure; this structure is similar to that found in the cellulose-binding domain of cellulase from Cellulomonas fimi.[1] This domain may function as a carbohydrate binding module.


  1. ^ a b Tews I, Perrakis A, Oppenheim A, Dauter Z, Wilson KS, Vorgias CE (July 1996). "Bacterial chitobiase structure provides insight into catalytic mechanism and the basis of Tay-Sachs disease". Nat. Struct. Biol. 3 (7): 638–48. doi:10.1038/nsb0796-638. PMID 8673609. 
  2. ^ Mark BL, Mahuran DJ, Cherney MM, Zhao D, Knapp S, James MN (April 2003). "Crystal structure of human beta-hexosaminidase B: understanding the molecular basis of Sandhoff and Tay-Sachs disease". J. Mol. Biol. 327 (5): 1093–109. doi:10.1016/S0022-2836(03)00216-X. PMC 2910754. PMID 12662933. 

This article incorporates text from the public domain Pfam and InterPro IPR004866

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.

Putative carbohydrate binding domain Provide feedback

This domain represents the N terminal domain in chitobiases and beta-hexosaminidases EC: It is composed of a beta sandwich structure that is similar in structure to the cellulose binding domain of cellulase from Cellulomonas fimi [1]. This suggests that this may be a carbohydrate binding domain.

Literature references

  1. Tews I, Perrakis A, Oppenheim A, Dauter Z, Wilson KS, Vorgias CE; , Nat Struct Biol 1996;3:638-648.: Bacterial chitobiase structure provides insight into catalytic mechanism and the basis of Tay-Sachs disease. PUBMED:8673609 EPMC:8673609

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR004866

This domain is found in the N terminus of chitobiases and beta-hexosaminidases. It is composed of a beta sandwich structure that is similar in structure to the cellulose binding domain of cellulase from Cellulomonas fimi [PUBMED:8673609], suggesting that it may function as a carbohydrate-binding domain.

Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Pfam Clan

This family is a member of clan CBD (CL0203), which has the following description:

This superfamily includes several carbohydrate binding domains. These domains have a beta sandwich structure.

The clan contains the following 5 members:

CBM49 CBM_2 CBM_3 CHB_HEX Cohesin


We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database using the family HMM. We also generate alignments using four representative proteomes (RP) sets, the NCBI sequence database, and our metagenomics sequence database. More...

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We make a range of alignments for each Pfam-A family. You can see a description of each above. You can view these alignments in various ways but please note that some types of alignment are never generated while others may not be available for all families, most commonly because the alignments are too large to handle.

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You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.

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MyHits provides a collection of tools to handle multiple sequence alignments. For example, one can refine a seed alignment (sequence addition or removal, re-alignment or manual edition) and then search databases for remote homologs using HMMER3.

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HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...


This page displays the phylogenetic tree for this family's seed alignment. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed alignment.

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Curation and family details

This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.

Curation View help on the curation process

Seed source: Pfam-B_8666 (release 6.5)
Previous IDs: none
Type: Domain
Author: Bateman A
Number in seed: 32
Number in full: 803
Average length of the domain: 154.20 aa
Average identity of full alignment: 39 %
Average coverage of the sequence by the domain: 19.38 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 80369284 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 25.0 25.0
Trusted cut-off 25.5 25.5
Noise cut-off 24.9 24.9
Model length: 159
Family (HMM) version: 9
Download: download the raw HMM for this family

Species distribution

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Colour assignments

Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the adjacent tab. More...

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There are 2 interactions for this family. More...

Glyco_hydro_20 CHB_HEX_C


For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the CHB_HEX domain has been found. There are 4 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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