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PSAP 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). Defects in PSAP are the cause of combined saposin deficiency (CSAPD); 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. Defects in PSAP saposin-B region are the cause of leukodystrophy metachromatic due to saposin-B deficiency (MLD- SAPB). 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. Defects in PSAP saposin-C region are the cause of atypical Gaucher disease (AGD). 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. Defects in PSAP saposin-A region are the cause of atypical Krabbe disease (AKRD). AKRD is a disorder of galactosylceramide metabolism. AKRD features include progressive encephalopathy and abnormal myelination in the cerebral white matter resembling Krabbe disease. Defects in PSAP saposin-D region are found in a variant of Tay-Sachs disease (GM2-gangliosidosis). 3 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.
Chromosomal Location of Human Ortholog: 10q22.1
Cellular Component: extracellular matrix; extracellular region; extracellular space; integral component of membrane; intracellular membrane-bound organelle; lysosomal lumen; lysosomal membrane; lysosome; mitochondrion; plasma membrane
Molecular Function: beta-galactosidase activity; enzyme activator activity; G-protein coupled receptor binding; lipid binding; phospholipid binding; protein binding; protein homodimerization activity
Biological Process: G-protein signaling, adenylate cyclase inhibiting pathway; glycosphingolipid metabolic process; lipid transport; neutrophil degranulation; platelet degranulation; positive regulation of catalytic activity; positive regulation of MAPK cascade; regulation of autophagy; regulation of lipid metabolic process
Disease: Combined Saposin Deficiency; Gaucher Disease, Atypical, Due To Saposin C Deficiency; Krabbe Disease, Atypical, Due To Saposin A Deficiency; Metachromatic Leukodystrophy Due To Saposin B Deficiency
Reference #:  P07602 (UniProtKB)
Alt. Names/Synonyms: A1 activator; Cerebroside sulfate activator; Co-beta-glucosidase; Component C; CSAct; Dispersin; FLJ00245; GLBA; Glucosylceramidase activator; MGC110993; Proactivator polypeptide; prosaposin; Protein A; Protein C; PSAP; SAP; SAP-1; SAP-2; SAP1; Saposin-A; Saposin-B; Saposin-B-Val; Saposin-C; Saposin-D; Sphingolipid activator protein 1; Sphingolipid activator protein 2; sphingolipid activator protein-1; Sulfatide/GM1 activator
Gene Symbols: PSAP
Molecular weight: 58,113 Da
Basal Isoelectric point: 5.06  Predict pI for various phosphorylation states
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