| Comment type | Description |
|---|
| Alternative Products | Event=Alternative splicing; Named isoforms=3; Comment=Additional isoforms seem to exist.; Name=Sap-mu-0; IsoId=P07602-1; Sequence=Displayed; Name=Sap-mu-6; IsoId=P07602-2; Sequence=VSP_006014; Name=Sap-mu-9; IsoId=P07602-3; Sequence=VSP_006015; |
| Disease | Combined saposin deficiency (CSAPD) [MIM |
| Disease | Gaucher disease, atypical, due to saposin C deficiency (AGD) [MIM |
| Disease | Krabbe disease, atypical, due to saposin A deficiency (AKRD) [MIM |
| Disease | Leukodystrophy metachromatic due to saposin-B deficiency (MLD-SAPB) [MIM |
| Disease | Note=Defects in PSAP saposin-D region are found in a variant of Tay-Sachs disease (GM2-gangliosidosis). |
| Function | Prosaposin: Behaves as a myelinotrophic and neurotrophic factor, these effects are mediated by its G-protein-coupled receptors, GPR37 and GPR37L1, undergoing ligand-mediated internalization followed by ERK phosphorylation signaling. |
| Function | Saposin-A and saposin-C stimulate the hydrolysis of glucosylceramide by beta-glucosylceramidase (EC 3.2.1.45) and galactosylceramide by beta-galactosylceramidase (EC 3.2.1.46). Saposin-C apparently acts by combining with the enzyme and acidic lipid to form an activated complex, rather than by solubilizing the substrate. |
| Function | Saposin-B stimulates the hydrolysis of galacto- cerebroside sulfate by arylsulfatase A (EC 3.1.6.8), GM1 gangliosides by beta-galactosidase (EC 3.2.1.23) and globotriaosylceramide by alpha-galactosidase A (EC 3.2.1.22). Saposin-B forms a solubilizing complex with the substrates of the sphingolipid hydrolases. |
| Function | Saposin-D is a specific sphingomyelin phosphodiesterase activator (EC 3.1.4.12). |
| Function | Saposins are specific low-molecular mass non-enzymic proteins, they participate in the lysosomal degradation of sphingolipids, which takes place by the sequential action of specific hydrolases. |
| Miscellaneous | Saposin-B co-purifies with 1 molecule of phosphatidylethanolamine. |
| Ptm | N-linked glycans show a high degree of microheterogeneity. |
| Ptm | The lysosomal precursor is proteolytically processed to 4 small peptides, which are similar to each other and are sphingolipid hydrolase activator proteins. |
| Ptm | The one residue extended Saposin-B-Val is only found in 5% of the chains. |
| Similarity | Contains 2 saposin A-type domains. |
| Similarity | Contains 4 saposin B-type domains. |
| Subcellular Location | Lysosome {ECO |
| Subcellular Location | Prosaposin: Secreted. Note=Secreted as a fully glycosylated 70 kDa protein composed of complex glycans. |
| Subunit | Saposin-B is a homodimer. Prosaposin exists as a roughly half-half mixture of monomers and disulfide-linked dimers. Monomeric prosaposin interacts (via C-terminus) with sortilin/SORT1, the interaction is required for targeting to lysosomes. {ECO |
| Web Resource | Name=Atlas of Genetics and Cytogenetics in Oncology and Haematology; URL="http://atlasgeneticsoncology.org/Genes/PSAPID42980ch10q22.html"; |