SapBSaposin (B) Domains |
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| SMART accession number: | SM00741 |
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| Description: | Present in multiple copies in prosaposin and in pulmonary surfactant-associated protein B. In plant aspartic proteinases, a saposin domain is circularly permuted. This causes the prediction algorithm to predict two such domains, where only one is truly present. |
| Interpro abstract (IPR008139): | Saposins are small lysosomal proteins that serve as activators of various lysosomal lipid-degrading enzymes [(PUBMED:7595087)]. 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 synthesised 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 [(PUBMED:8003971), (PUBMED:8868085)]. The 3D-structure of NK-lysin has recently been determined [(PUBMED:9334742)] and found to be very different from the one predicted in [(PUBMED:7595087)]. A group of plant aspartic proteases related to cyprosin, which have a peculiar SAP-B domain where the two halves are 'swapped' [(PUBMED:7610480)]. |
| Family alignment: |
There are 1250 SapB domains in 642 proteins in SMART's nrdb database.
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- Evolution (species in which this domain is found)
- Cellular role (predicted cellular role)
- Metabolism (metabolic pathways involving proteins which contain this domain)
- Structure (3D structures containing this domain)
- Links (links to other resources describing this domain)
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