Summary: Saposin-like type B, region 1
This is the Wikipedia entry entitled "Saposin protein domain". More...
Does Pfam agree with the content of the Wikipedia entry ?
Editing Wikipedia articles
Before you edit for the first time
You should take a few minutes to view the following pages:
How your contribution will be recorded
Saposin protein domain Edit Wikipedia article
|Saposin-like type B, region 1|
Crystal structure of human saposin C dimer in an open conformation.
In molecular biology a saposin protein domain is a region of the saposin protein that has a certain conserved sequence or structure that defines a domain. Saposins are small lysosomal proteins that serve as activators of various lysosomal lipid-degrading enzymes. They probably act by isolating the lipid substrate from the membrane surroundings, thus making it more accessible to the soluble degradative enzymes. All mammalian saposins are synthesized as a single precursor molecule (prosaposin) which contains four Saposin-B domains, yielding the active saposins after proteolytic cleavage, and two Saposin-A domains that are removed in the activation reaction. The Saposin-B domains also occur in other proteins, many of them active in the lysis of membranes.
Below is a schematic diagram of the primary structure of the prosaposin protein depicting the N- and C-terminal SapA domains and the four SapB1 and four SapB2 domains. Proteolytic cleavage of the proprotein occurs in the grey regions. Adjacent pairs of SapB1 and SapB2 domains remain connected after proteolytic processing of prosaposin and each pair comprises one of the mature saponin A-D proteins.
Human proteins containing this domain
- PDB 2qyp, Rossmann M, Schultz-Heienbrok R, Behlke J, Remmel N, Alings C, Sandhoff K, Saenger W, Maier T (May 2008). "Crystal structures of human saposins C and D: implications for lipid recognition and membrane interactions". Structure 16 (5): 809–17. doi:10.1016/j.str.2008.02.016. PMID 18462685.
- Munford RS, Sheppard PO, O Hara PJ (1995). "Saposin-like proteins (SAPLIP) carry out diverse functions on a common backbone structure". J. Lipid Res. 36 (8): 1653–1663. PMID 7595087.
- Ponting CP (1994). "Acid sphingomyelinase possesses a domain homologous to its activator proteins: saposins B and D". Protein Sci. 3 (2): 359–361. doi:10.1002/pro.5560030219. PMC 2142785. PMID 8003971.
- Hofmann K, Tschopp J (1996). "Cytotoxic T cells: more weapons for new targets?". Trends Microbiol. 4 (3): 91–94. doi:10.1016/0966-842X(96)81522-8. PMID 8868085.
|This membrane protein–related article is a stub. You can help Wikipedia by expanding it.|
Saposin-like type B, region 1 Provide feedback
No Pfam abstract.
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR007856
Synonym(s):cerebroside sulphate activator, CSAct
Saposin B is a small non-enzymatic glycoprotein required for the breakdown of cerebroside sulphates (sulphatides) in lysosomes. Saposin B contains three intramolecular disulphide bridges, exists as a dimer and is remarkably heat, protease, and pH stable. The crystal structure of human saposin B reveals an unusual shell-like dimer consisting of a monolayer of alpha-helices enclosing a large hydrophobic cavity. Although the secondary structure of saposin B is similar to that of the known monomeric members of the saposin-like superfamily, the helices are repacked into a different tertiary arrangement to form the homodimer. A comparison of the two forms of the saposin B dimer suggests that extraction of target lipids from membranes involves a conformational change that facilitates access to the inner cavity [PUBMED:12518053].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Biological process||lipid metabolic process (GO:0006629)|
- the number of sequences which exhibit this architecture
a textual description of the architecture, e.g. Gla, EGF x 2, Trypsin.
This example describes an architecture with one
Gladomain, followed by two consecutive
EGFdomains, and finally a single
- the UniProt description of the protein sequence
- the number of residues in the sequence
- the Pfam graphic itself.
Loading domain graphics...
We make a range of alignments for each Pfam-A family:
- the curated alignment from which the HMM for the family is built
- the alignment generated by searching the sequence database using the HMM
- Representative Proteomes (RPs) at 15%, 35%, 55% and 75% co-membership thresholds
- alignment generated by searching the NCBI sequence database using the family HMM
- alignment generated by searching the metagenomics sequence database using the family HMM
You can see the alignments as HTML or in three different sequence viewers:
- Pfam viewer
- an HTML-based viewer that uses DAS to retrieve alignment fragments on request
1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
Format an alignment
If you find these logos useful in your own work, please consider citing the following article:
Note: You can also download the data file for the tree.
Curation and family details
|Number in seed:||161|
|Number in full:||1396|
|Average length of the domain:||38.80 aa|
|Average identity of full alignment:||27 %|
|Average coverage of the sequence by the domain:||19.67 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||10|
|Download:||download the raw HMM for this family|
Weight segments by...
Change the size of the sunburst
selected sequences to HMM
a FASTA-format file
- 0 sequences
- 0 species
How the sunburst is generated
Colouring and labels
Anomalies in the taxonomy tree
Missing taxonomic levels
Unmapped species names
Too many species/sequences
The tree shows the occurrence of this domain across different species. More...
You can use the tree controls to manipulate how the interactive tree is displayed:
- show/hide the summary boxes
- highlight species that are represented in the seed alignment
- expand/collapse the tree or expand it to a given depth
- select a sub-tree or a set of species within the tree and view them graphically or as an alignment
- save a plain text representation of the tree
There are 2 interactions for this family. More...
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 SapB_1 domain has been found. There are 31 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.
Loading structure mapping...