1sn6

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1sn6, 20 NMR models ()
Gene: PSAP (Homo sapiens)
Related: 1m12
Resources: FirstGlance, OCA, RCSB, PDBsum
Coordinates: save as pdb, mmCIF, xml


Contents

NMR solution structure of human Saposin C in SDS micelles

Publication Abstract from PubMed

Saposin C is a lysosomal, membrane-binding protein that acts as an activator for the hydrolysis of glucosylceramide by the enzyme glucocerebrosidase. We used high-resolution NMR to determine the three-dimensional solution structure of saposin C in the presence of the detergent sodium dodecyl sulfate (SDS). This structure provides the first representation of membrane bound saposin C at the atomic level. In the presence of SDS, the protein adopts an open conformation with an exposed hydrophobic pocket. In contrast, the previously reported NMR structure of saposin C in the absence of SDS is compact and contains a hydrophobic core that is not exposed to the solvent. NMR data indicate that the SDS molecules interact with the hydrophobic pocket. The structure of saposin C in the presence of SDS is very similar to a monomer in the saposin B homodimer structure. Their comparison reveals possible similarity in the type of protein/lipid interaction as well as structural components differentiating their quaternary structures and functional specificity.

Solution structure of human saposin C in a detergent environment., Hawkins CA, de Alba E, Tjandra N, J Mol Biol. 2005 Mar 11;346(5):1381-92. Epub 2005 Jan 20. PMID:15713488

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

Disease

[SAP_HUMAN] 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.[1][2] 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. 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.[3][4] 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.[5] Note=Defects in PSAP saposin-D region are found in a variant of Tay-Sachs disease (GM2-gangliosidosis).

Function

[SAP_HUMAN] 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). 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. 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. Saposin-D is a specific sphingomyelin phosphodiesterase activator (EC 3.1.4.12).

About this Structure

1sn6 is a 1 chain structure with sequence from Homo sapiens. Full experimental information is available from OCA.

See Also

Reference

  • Hawkins CA, de Alba E, Tjandra N. Solution structure of human saposin C in a detergent environment. J Mol Biol. 2005 Mar 11;346(5):1381-92. Epub 2005 Jan 20. PMID:15713488 doi:10.1016/j.jmb.2004.12.045
  • de Alba E, Weiler S, Tjandra N. Solution structure of human saposin C: pH-dependent interaction with phospholipid vesicles. Biochemistry. 2003 Dec 23;42(50):14729-40. PMID:14674747 doi:10.1021/bi0301338
  1. Schnabel D, Schroder M, Furst W, Klein A, Hurwitz R, Zenk T, Weber J, Harzer K, Paton BC, Poulos A, et al.. Simultaneous deficiency of sphingolipid activator proteins 1 and 2 is caused by a mutation in the initiation codon of their common gene. J Biol Chem. 1992 Feb 15;267(5):3312-5. PMID:1371116
  2. Hulkova H, Cervenkova M, Ledvinova J, Tochackova M, Hrebicek M, Poupetova H, Befekadu A, Berna L, Paton BC, Harzer K, Boor A, Smid F, Elleder M. A novel mutation in the coding region of the prosaposin gene leads to a complete deficiency of prosaposin and saposins, and is associated with a complex sphingolipidosis dominated by lactosylceramide accumulation. Hum Mol Genet. 2001 Apr 15;10(9):927-40. PMID:11309366
  3. Schnabel D, Schroder M, Sandhoff K. Mutation in the sphingolipid activator protein 2 in a patient with a variant of Gaucher disease. FEBS Lett. 1991 Jun 17;284(1):57-9. PMID:2060627
  4. Tylki-Szymanska A, Czartoryska B, Vanier MT, Poorthuis BJ, Groener JA, Lugowska A, Millat G, Vaccaro AM, Jurkiewicz E. Non-neuronopathic Gaucher disease due to saposin C deficiency. Clin Genet. 2007 Dec;72(6):538-42. Epub 2007 Oct 7. PMID:17919309 doi:http://dx.doi.org/10.1111/j.1399-0004.2007.00899.x
  5. Spiegel R, Bach G, Sury V, Mengistu G, Meidan B, Shalev S, Shneor Y, Mandel H, Zeigler M. A mutation in the saposin A coding region of the prosaposin gene in an infant presenting as Krabbe disease: first report of saposin A deficiency in humans. Mol Genet Metab. 2005 Feb;84(2):160-6. PMID:15773042

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