Prosaposin
Prosaposin,also known asPSAP,is aproteinwhich in humans is encoded by thePSAPgene.[5]
This highly conservedglycoproteinis a precursor for 4 cleavage products:saposinsA, B, C, and D. Saposin is an acronym forSphingolipidActivatorPrO[S]teINs.[6]Each domain of the precursor protein is approximately 80 amino acid residues long with nearly identical placement of cysteine residues and glycosylation sites. Saposins A-D localize primarily to thelysosomalcompartment where they facilitate the catabolism ofglycosphingolipidswith shortoligosaccharidegroups. The precursor protein exists both as a secretory protein and as an integral membrane protein and hasneurotrophicactivities.[5]
Saposins A–D are required for the hydrolysis of certain sphingolipids by specific lysosomal hydrolases.[7]
Family members
[edit]- Saposin Awas identified as an N-terminal domain in the prosaposin cDNA prior to its isolation. It is known to stimulate the enzymatic hydrolysis of 4-methylumbelliferyl-β-glucoside,glucocerebroside,andgalactocerebroside.[8]
- Saposin Bwas the first to be discovered and was found to be required as a heat-stable factor for hydrolysis ofsulfatidesbyarylsulfatase A.It is known by many different names, such as, sphingolipid activator protein-1 (SAP-1), sulfatide activator protein, GM1ganglioside activator, dispersin, and nonspecific.[9]It has been observed that this particular saposin activates many enzymes through interaction with the substrates not the enzymes themselves.
- Saposin Cwas the second saposin to be discovered and stimulates the hydrolysis of glycocerebroside by glycosylceramidase and galactocerebroside by galactosylceramidase.
- Saposin Dis not well known to due lack of investigation at this point in time. It was predicted from the cDNA sequence of prosaposin, like saposin A. Enzymatic stimulation is very specific for this particular glycoprotein and it not understood completely.[7]
- GM2A(GM2 ganglioside activator) has been viewed as a member of the SAP family and has been called SAP-3 (sphingolipid activator protein 3)[10]
Structure
[edit]Every saposin contains about 80 amino acid residues and has six equally placed cysteines, two prolines, and a glycosylation site (two in saposin A, one each in saposins B, C, and D).[7]Since saposins characteristics of extreme heat-stability, abundance of disulfide linkages, and resistance to most proteases, they are assumed to be extremely compact and rigidly disulfide-linked molecules. Each saposin has an α-helical structure that is seen as being important for stimulation because this structure is maximal at a pH of 4.5; which is optimal for many lysosomal hydrolases.[7]This helical structure is seen in all (especially with the first region), but saposin has been predicted to have β-sheet configuration due to it first 24 amino acids of the N-end.[9]
Function
[edit]They probably act by isolating the lipid substrate from the membrane surroundings, thus making it more accessible to the solubledegradative enzymes.which contains fourSaposin-B domains,yielding the active saposins after proteolytic cleavage, and twoSaposin-A domainsthat are removed in the activation reaction. The Saposin-B domains also occur in other proteins, many of them active in the lysis of membranes.[14][15]
Clinical significance
[edit]Mutations in this gene have been associated withGaucher disease,Tay–Sachs disease,andmetachromatic leukodystrophy.[6]
See also
[edit]References
[edit]- ^abcGRCh38: Ensembl release 89: ENSG00000197746–Ensembl,May 2017
- ^abcGRCm38: Ensembl release 89: ENSMUSG00000004207–Ensembl,May 2017
- ^"Human PubMed Reference:".National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^"Mouse PubMed Reference:".National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ab"Entrez Gene: PSAP prosaposin (variant Gaucher disease and variant metachromatic leukodystrophy)".
- ^abMorimoto S, Yamamoto Y, O'Brien JS, Kishimoto Y (May 1990)."Distribution of saposin proteins (sphingolipid activator proteins) in lysosomal storage and other diseases".Proc. Natl. Acad. Sci. U.S.A.87(9): 3493–7.Bibcode:1990PNAS...87.3493M.doi:10.1073/pnas.87.9.3493.PMC53927.PMID2110365.
- ^abcdKishimoto Y, Hiraiwa M, O'Brien JS (September 1992)."Saposins: structure, function, distribution, and molecular genetics".J. Lipid Res.33(9): 1255–67.doi:10.1016/S0022-2275(20)40540-1.PMID1402395.
- ^Morimoto S, Martin BM, Yamamoto Y, Kretz KA, O'Brien JS, Kishimoto Y (May 1989)."Saposin A: second cerebrosidase activator protein".Proc. Natl. Acad. Sci. U.S.A.86(9): 3389–93.Bibcode:1989PNAS...86.3389M.doi:10.1073/pnas.86.9.3389.PMC287138.PMID2717620.
- ^abO'Brien JS, Kishimoto Y (March 1991)."Saposin proteins: structure, function, and role in human lysosomal storage disorders".FASEB J.5(3): 301–8.doi:10.1096/fasebj.5.3.2001789.PMID2001789.S2CID40251569.
- ^HUGO Gene Nomenclature Committee,"GM2A",HGNC database,retrieved2016-03-13.
- ^Ahn VE, Leyko P, Alattia JR, Chen L, Privé GG (August 2006)."Crystal structures of saposins A and C".Protein Sci.15(8): 1849–57.doi:10.1110/ps.062256606.PMC2242594.PMID16823039.
- ^Ahn VE, Faull KF, Whitelegge JP, Fluharty AL, Privé GG (January 2003)."Crystal structure of saposin B reveals a dimeric shell for lipid binding".Proc. Natl. Acad. Sci. U.S.A.100(1): 38–43.Bibcode:2003PNAS..100...38A.doi:10.1073/pnas.0136947100.PMC140876.PMID12518053.
- ^abRossmann M, Schultz-Heienbrok R, Behlke J, Remmel N, Alings C, Sandhoff K, Saenger W, Maier T (May 2008)."Crystal structures of human saposins C and D: implications for lipid recognition and membrane interactions".Structure.16(5): 809–17.doi:10.1016/j.str.2008.02.016.PMID18462685.
- ^Ponting CP (1994)."Acid sphingomyelinase possesses a domain homologous to its activator proteins: saposins B and D".Protein Sci.3(2): 359–361.doi:10.1002/pro.5560030219.PMC2142785.PMID8003971.
- ^Hofmann K, Tschopp J (1996). "Cytotoxic T cells: more weapons for new targets?".Trends Microbiol.4(3): 91–94.doi:10.1016/0966-842X(96)81522-8.PMID8868085.
Further reading
[edit]- Gieselmann V, Zlotogora J, Harris A, et al. (1995)."Molecular genetics of metachromatic leukodystrophy".Hum. Mutat.4(4): 233–42.doi:10.1002/humu.1380040402.PMID7866401.S2CID23519007.
- Schnabel D, Schröder M, Fürst W, et al. (1992)."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.267(5): 3312–5.doi:10.1016/S0021-9258(19)50733-5.PMID1371116.
- Hiraiwa M, Soeda S, Kishimoto Y, O'Brien JS (1993)."Binding and transport of gangliosides by prosaposin".Proc. Natl. Acad. Sci. U.S.A.89(23): 11254–8.doi:10.1073/pnas.89.23.11254.PMC50528.PMID1454804.
- Rorman EG, Scheinker V, Grabowski GA (1992). "Structure and evolution of the human prosaposin chromosomal gene".Genomics.13(2): 312–8.doi:10.1016/0888-7543(92)90247-P.PMID1612590.
- Kondoh K, Hineno T, Sano A, Kakimoto Y (1992). "Isolation and characterization of prosaposin from human milk".Biochem. Biophys. Res. Commun.181(1): 286–92.doi:10.1016/S0006-291X(05)81415-9.PMID1958198.
- Holtschmidt H, Sandhoff K, Fürst W, et al. (1991)."The organization of the gene for the human cerebroside sulfate activator protein".FEBS Lett.280(2): 267–70.doi:10.1016/0014-5793(91)80308-P.PMID2013321.S2CID38952277.
- Holtschmidt H, Sandhoff K, Kwon HY, et al. (1991)."Sulfatide activator protein. Alternative splicing that generates three mRNAs and a newly found mutation responsible for a clinical disease".J. Biol. Chem.266(12): 7556–60.doi:10.1016/S0021-9258(20)89483-6.PMID2019586.
- Hineno T, Sano A, Kondoh K, et al. (1991). "Secretion of sphingolipid hydrolase activator precursor, prosaposin".Biochem. Biophys. Res. Commun.176(2): 668–74.doi:10.1016/S0006-291X(05)80236-0.PMID2025281.
- Schnabel D, Schröder M, Sandhoff K (1991). "Mutation in the sphingolipid activator protein 2 in a patient with a variant of Gaucher disease".FEBS Lett.284(1): 57–9.doi:10.1016/0014-5793(91)80760-Z.PMID2060627.S2CID42681055.
- Zhang XL, Rafi MA, DeGala G, Wenger DA (1991). "The mechanism for a 33-nucleotide insertion in mRNA causing sphingolipid activator protein (SAP-1)-deficient metachromatic leukodystrophy".Hum. Genet.87(2): 211–5.doi:10.1007/BF00204185.PMID2066109.S2CID23791396.
- Fürst W, Schubert J, Machleidt W, et al. (1990). "The complete amino-acid sequences of human ganglioside GM2 activator protein and cerebroside sulfate activator protein".Eur. J. Biochem.192(3): 709–14.doi:10.1111/j.1432-1033.1990.tb19280.x.PMID2209618.
- Rafi MA, Zhang XL, DeGala G, Wenger DA (1990). "Detection of a point mutation in sphingolipid activator protein-1 mRNA in patients with a variant form of metachromatic leukodystrophy".Biochem. Biophys. Res. Commun.166(2): 1017–23.doi:10.1016/0006-291X(90)90912-7.PMID2302219.
- Kretz KA, Carson GS, Morimoto S, et al. (1990)."Characterization of a mutation in a family with saposin B deficiency: a glycosylation site defect".Proc. Natl. Acad. Sci. U.S.A.87(7): 2541–4.Bibcode:1990PNAS...87.2541K.doi:10.1073/pnas.87.7.2541.PMC53725.PMID2320574.
- Nakano T, Sandhoff K, Stümper J, et al. (1989). "Structure of full-length cDNA coding for sulfatide activator, a Co-beta-glucosidase and two other homologous proteins: two alternate forms of the sulfatide activator".J. Biochem.105(2): 152–4.doi:10.1093/oxfordjournals.jbchem.a122629.PMID2498298.
- Rorman EG, Grabowski GA (1990). "Molecular cloning of a human co-beta-glucosidase cDNA: evidence that four sphingolipid hydrolase activator proteins are encoded by single genes in humans and rats".Genomics.5(3): 486–92.doi:10.1016/0888-7543(89)90014-1.PMID2515150.
- Morimoto S, Martin BM, Yamamoto Y, et al. (1989)."Saposin A: second cerebrosidase activator protein".Proc. Natl. Acad. Sci. U.S.A.86(9): 3389–93.Bibcode:1989PNAS...86.3389M.doi:10.1073/pnas.86.9.3389.PMC287138.PMID2717620.
- Dewji NN, Wenger DA, O'Brien JS (1988)."Nucleotide sequence of cloned cDNA for human sphingolipid activator protein 1 precursor".Proc. Natl. Acad. Sci. U.S.A.84(23): 8652–6.doi:10.1073/pnas.84.23.8652.PMC299604.PMID2825202.
- O'Brien JS, Kretz KA, Dewji N, et al. (1988). "Coding of two sphingolipid activator proteins (SAP-1 and SAP-2) by same genetic locus".Science.241(4869): 1098–101.Bibcode:1988Sci...241.1098O.doi:10.1126/science.2842863.PMID2842863.
- Morimoto S, Martin BM, Kishimoto Y, O'Brien JS (1988)."Saposin D: a sphingomyelinase activator".Biochem. Biophys. Res. Commun.156(1): 403–10.doi:10.1016/S0006-291X(88)80855-6.PMID2845979.
- Dewji N, Wenger D, Fujibayashi S, et al. (1986). "Molecular cloning of the sphingolipid activator protein-1 (SAP-1), the sulfatide sulfatase activator".Biochem. Biophys. Res. Commun.134(2): 989–94.doi:10.1016/S0006-291X(86)80518-6.PMID2868718.
External links
[edit]- Saposinsat the U.S. National Library of MedicineMedical Subject Headings(MeSH)