ID:SAP_HUMAN DESCRIPTION: RecName: Full=Proactivator polypeptide; Contains: RecName: Full=Saposin-A; AltName: Full=Protein A; Contains: RecName: Full=Saposin-B-Val; Contains: RecName: Full=Saposin-B; AltName: Full=Cerebroside sulfate activator; Short=CSAct; AltName: Full=Dispersin; AltName: Full=Sphingolipid activator protein 1; Short=SAP-1; AltName: Full=Sulfatide/GM1 activator; Contains: RecName: Full=Saposin-C; AltName: Full=A1 activator; AltName: Full=Co-beta-glucosidase; AltName: Full=Glucosylceramidase activator; AltName: Full=Sphingolipid activator protein 2; Short=SAP-2; Contains: RecName: Full=Saposin-D; AltName: Full=Component C; AltName: Full=Protein C; Flags: Precursor; FUNCTION: The lysosomal degradation of sphingolipids takes place by the sequential action of specific hydrolases. Some of these enzymes require specific low-molecular mass, non-enzymic proteins: the sphingolipids activator proteins (coproteins). 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). SUBUNIT: Saposin-B is a homodimer. SUBCELLULAR LOCATION: Lysosome. PTM: This precursor is proteolytically processed to 4 small peptides, which are similar to each other and are sphingolipid hydrolase activator proteins. PTM: N-linked glycans show a high degree of microheterogeneity. PTM: The one residue extended Saposin-B-Val is only found in 5% of the chains. DISEASE: Defects in PSAP are the cause of combined saposin deficiency (CSAPD) [MIM:611721]; also known as prosaposin deficiency. CSAPD is due to absence of all saposins, leading to a fatal storage disorder with hepatosplenomegaly and severe neurological involvement. DISEASE: Defects in PSAP saposin-B region are the cause of leukodystrophy metachromatic due to saposin-B deficiency (MLD- SAPB) [MIM:249900]. MLD-SAPB is an atypical form of metachromatic leukodystrophy. It is characterized by tissue accumulation of cerebroside-3-sulfate, demyelination, periventricular white matter abnormalities, peripheral neuropathy. Additional neurological features include dysarthria, ataxic gait, psychomotr regression, seizures, cognitive decline and spastic quadriparesis. DISEASE: Defects in PSAP saposin-C region are the cause of atypical Gaucher disease (AGD) [MIM:610539]. Affected individuals have marked glucosylceramide accumulation in the spleen without having a deficiency of glucosylceramide-beta glucosidase characteristic of classic Gaucher disease, a lysosomal storage disorder. DISEASE: Defects in PSAP saposin-A region are the cause of atypical Krabbe disease (AKRD) [MIM:611722]. AKRD is a disorder of galactosylceramide metabolism. AKRD features include progressive encephalopathy and abnormal myelination in the cerebral white matter resembling Krabbe disease. DISEASE: Note=Defects in PSAP saposin-D region are found in a variant of Tay-Sachs disease (GM2-gangliosidosis). MISCELLANEOUS: Saposin-B co-purifies with 1 molecule of phosphatidylethanolamine. SIMILARITY: Contains 2 saposin A-type domains. SIMILARITY: Contains 4 saposin B-type domains. WEB RESOURCE: Name=Atlas of Genetics and Cytogenetics in Oncology and Haematology; URL="http://atlasgeneticsoncology.org/Genes/PSAPID42980ch10q22.html"; WEB RESOURCE: Name=GeneReviews; URL="http://www.ncbi.nlm.nih.gov/sites/GeneTests/lab/gene/PSAP";
The RNAfold program from the Vienna RNA Package is used to perform the secondary structure predictions and folding calculations. The estimated folding energy is in kcal/mol. The more negative the energy, the more secondary structure the RNA is likely to have.
ModBase Predicted Comparative 3D Structure on P07602
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Orthologous Genes in Other Species
Orthologies between human, mouse, and rat are computed by taking the best BLASTP hit, and filtering out non-syntenic hits. For more distant species reciprocal-best BLASTP hits are used. Note that the absence of an ortholog in the table below may reflect incomplete annotations in the other species rather than a true absence of the orthologous gene.
US Server
Sequence and Links to Tools and Databases 
Common Gene Haplotype Alleles 
