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83  structures 2087  species 2  interactions 5996  sequences 193  architectures

Family: Glyco_hydro_20b (PF02838)

Summary: Glycosyl hydrolase family 20, domain 2

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This is the Wikipedia entry entitled "Glycoside hydrolase family 20". More...

Glycoside hydrolase family 20 Edit Wikipedia article

Glycosyl hydrolase family 20, catalytic domain
PDB 1m01 EBI.jpg
wildtype streptomyces plicatus beta-hexosaminidase in complex with product (glcnac)
Symbol Glyco_hydro_20
Pfam PF00728
Pfam clan CL0058
InterPro IPR015883
SCOP 1qba
CDD cd02742
Glycosyl hydrolase family 20, domain 2
PDB 2gjx EBI.jpg
crystallographic structure of human beta-hexosaminidase a
Symbol Glyco_hydro_20b
Pfam PF02838
InterPro IPR015882
SCOP 1qba

In molecular biology, glycoside hydrolase family 20 is a family of glycoside hydrolases.

Glycoside hydrolases EC 3.2.1. are a widespread group of enzymes that hydrolyse the glycosidic bond between two or more carbohydrates, or between a carbohydrate and a non-carbohydrate moiety. A classification system for glycoside hydrolases, based on sequence similarity, has led to the definition of >100 different families.[1][2][3] This classification is available on the CAZy( web site,[4] and also discussed at CAZypedia, an online encyclopedia of carbohydrate active enzymes.[5]

Glycoside hydrolase family 20 CAZY GH_20 comprises enzymes with several known activities; beta-hexosaminidase (EC; lacto-N-biosidase (EC Carbonyl oxygen of the C-2 acetamido group of the substrate acts as the catalytic nucleophile/base in this family of enzymes.

In the brain and other tissues, beta-hexosaminidase A degrades GM2 gangliosides; specifically, the enzyme hydrolyses terminal non-reducing N-acetyl-D-hexosamine residues in N-acetyl-beta-D-hexosaminides. There are 3 forms of beta-hexosaminidase: hexosaminidase A is a trimer, with one alpha, one beta-A and one beta-B chain; hexosaminidase B is a tetramer of two beta-A and two beta-B chains; and hexosaminidase S is a homodimer of alpha chains. The two beta chains are derived from the cleavage of a precursor. Mutations in the beta-chain lead to Sandhoff disease, a lysosomal storage disorder characterised by accumulation of GM2 ganglioside.[6]


  1. ^ Henrissat B, Callebaut I, Mornon JP, Fabrega S, Lehn P, Davies G (1995). "Conserved catalytic machinery and the prediction of a common fold for several families of glycosyl hydrolases". Proc. Natl. Acad. Sci. U.S.A. 92 (15): 7090–7094. doi:10.1073/pnas.92.15.7090. PMC 41477. PMID 7624375. 
  2. ^ Henrissat B, Davies G (1995). "Structures and mechanisms of glycosyl hydrolases". Structure 3 (9): 853–859. doi:10.1016/S0969-2126(01)00220-9. PMID 8535779. 
  3. ^ Bairoch, A. "Classification of glycosyl hydrolase families and index of glycosyl hydrolase entries in SWISS-PROT". 1999.
  4. ^ Henrissat, B. and Coutinho P.M. "Carbohydrate-Active Enzymes server". 1999.
  5. ^ CAZypedia, an online encyclopedia of carbohydrate-active enzymes.
  6. ^ Bolhuis PA, Ponne NJ, Bikker H, Baas F, Vianney de Jong JM (1993). "Molecular basis of an adult form of Sandhoff disease: substitution of glutamine for arginine at position 505 of the beta-chain of beta-hexosaminidase results in a labile enzyme". Biochim. Biophys. Acta 1182 (2): 142–146. doi:10.1016/0925-4439(93)90134-m. PMID 8357844. 

This article incorporates text from the public domain Pfam and InterPro IPR015883

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.

Glycosyl hydrolase family 20, domain 2 Provide feedback

This domain has a zincin-like fold.

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

Internal database links

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR015882

This entry represents the N-terminal domain of the beta-hexosaminidases mostly from bacteria, some yeasts and invertebrates. This domain has a zincin-like fold and can be found in chitobiases, hyaluronoglucosaminidases, N,N'-diacetylchitobiases and O-GlcNAcase NagJ. They belong to either the glycosyl hydrolase 84 or the glycosyl hydrolase 20 families.

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 Hexosaminidase (CL0546), which has the following description:

This superfamily is characterised by a mixed beta sheet with connection over the free side of the sheet. The fold is like a zincin fold lacking the catalytic centre.

The clan contains the following 3 members:

Glyco_hydro_20b Glyco_hydro_67N Glycohydro_20b2


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

External links

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.

Note: You can also download the data file for the tree.

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_877 (release 2.1)
Previous IDs: glycosyl_hydr11;
Type: Domain
Author: Bateman A, Griffiths-Jones SR
Number in seed: 76
Number in full: 5996
Average length of the domain: 125.10 aa
Average identity of full alignment: 21 %
Average coverage of the sequence by the domain: 16.73 %

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 26.1 26.1
Trusted cut-off 26.1 26.1
Noise cut-off 26.0 26.0
Model length: 124
Family (HMM) version: 11
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...

NAGidase Glyco_hydro_20


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 Glyco_hydro_20b domain has been found. There are 83 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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