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0SAP_HUMAN*   SwissProt (?) | Description Local Annotation Link Reference
General Information
NamePSAP
DescriptionProactivator polypeptide precursor .
SpeciesHomo sapiens (NCBI taxonomy ID: 9606)
GO0005615 extracellular space (TAS)
0016021 integral to membrane (TAS)
0008047 enzyme activator activity (TAS)
0008289 lipid binding (TAS)
0006687 glycosphingolipid metabolism (TAS)
0006869 lipid transport (TAS)

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schematic display of those terms with internal associations, click the node and browse the corresponding GO term
Domain Architecture (Details)
InterPro domains unassigned to SynO:
Saposins are small lysosomal proteins that serve as activators of variouslysosomal lipid-degrading enzymes . They probably act by isolating thelipid substrate from the membrane surroundings.hus making it more accessible to the soluble degradative enzymes. All mammalian saposinsare synthesised as a single precursor molecule (prosaposin) which containsfour Saposin B domains.ielding the active saposins after proteolyticcleavage.nd two Saposin-A domains that are removed in the activationreaction. The Saposin B domains also occur in other proteins.any of them active in the lysis of membranes . The 3D-structure of NK-lysin has recently been determined and found tobe very different from the one predicted in .A group of plant aspartic proteases related to cyprosin.hich have a peculiar SAP-B domain where the two halves are swapped .
  IPR008139:Saposin B
Saposins are small lysosomal proteins that serve as activators of variouslysosomal lipid-degrading enzymes . They probably act by isolating thelipid substrate from the membrane surroundings.hus making it more accessible to the soluble degradative enzymes. All mammalian saposinsare synthesized as a single precursor molecule (prosaposin) which containsfour Saposin-B domains.ielding the active saposins after proteolyticcleavage.nd two Saposin-A domains that are removed in the activationreaction. The Saposin-B domains also occur in other proteins.any of them active in the lysis of membranes . The saposin A-type domain may play a role in targeting.s propeptides containing the saposin A-type domain of the C-terminus of prosaposin and of the N-terminal part of pulmonary surfactant-associated protein B are involved in the transport to the lysosome and to secretory granules (lamellar bodies.hich are lysosomal-like organelles).espectively .
  IPR003119:Saposin type A
Synonym(s):cerebroside sulphate activator.SAct Saposin B is a small non-enzymatic glycoprotein required for the breakdownof cerebroside sulphates (sulphatides) in lysosomes. Saposin B contains three intramolecular disulphide bridges.xists as a dimer and is remarkably heat.rotease.nd pH stable. The crystal structure of human saposin B reveals an unusual shell-like dimer consisting of a monolayer of alpha-helices enclosing a large hydrophobic cavity. Although the secondary structure of saposin B is similar to that of the known monomeric members of the saposin-like superfamily.he helices are repacked into a different tertiary arrangement to form the homodimer. A comparison of the two forms of the saposin B dimer suggests that extraction of target lipids from membranes involves a conformational change that facilitates access to the inner cavity .
  IPR007856:Saposin-like type B, 1
Saposins are small lysosomal proteins that serve as activators of variouslysosomal lipid-degrading enzymes . They probably act by isolating thelipid substrate from the membrane surroundings.hus making it more accessible to the soluble degradative enzymes. All mammalian saposinsare synthesized as a single precursor molecule (prosaposin) which containsfour Saposin-B domains.ielding the active saposins after proteolyticcleavage.nd two Saposin-A domains that are removed in the activationreaction. The Saposin-B domains also occur in other proteins.any of them active in the lysis of membranes .
  IPR008138:Saposin-like type B, 2
Saposins are small lysosomal proteins that serve as activators of variouslysosomal lipid-degrading enzymes . They probably act by isolating thelipid substrate from the membrane surroundings.hus making it more accessible to the soluble degradative enzymes. All mammalian saposinsare synthesized as a single precursor molecule (prosaposin) which containsfour Saposin B domains.ielding the active saposins after proteolyticcleavage.nd two Saposin-A domains that are removed in the activationreaction. The Saposin B domains also occur in other proteins.any of them active in the lysis of membranes .
  IPR008140:Saposin B subdomain
Sphingolipids are bioactive compounds found in lower and higher eukaryotes.They are involved in the regulation of various cellular functions.uch asgrowth.ifferentiation and apoptosis.nd are believed to be essential ina healthy diet. Sphigolipids are degraded in the lysosome.nd theproducts from their hydrolysis are used in other biosynthetic and regulatorypathways in the host.There are a number of lysosomal enzymes involved in the breakdown ofsphinogolipids.nd these act in sequence to degrade the moieties . These enzymes require co-proteins called sphingolipid activator proteins.SAPs or saposins).o stabilise and activate them as necessary. SAPs are non-enzymatic and usually have a low molecular weight. They are conserved across a wide range of eukaryotes and contain specific saposin domains that aid in the activation of hydrolase enzymes. There have been four human saposins described so far.haring significant similarity with each otherand with other eukaryotic SAP proteins.Mutations in SAP genes have been linked to a number of conditions. A defectin the saposin B region leads to metachromatic leucodystrophy (MLD).hilea single nucleotide polymorphism in the SAP-C region may give rise toGaucher disease . More recently.n opportunistic protozoan parasiteprotein has shown similarity both to the higher and lower eukaryoticsaposins. The pore-forming protein isolated from virulent Naegleriafowleri trophoziotes has been dubbed Naegleriapore A. It also sharesstructural similarity with cytolytic bacterial peptides.lthough thissimilarity does not extend to the sequence level.
  IPR008373:Saposin
Peptidases are grouped into clans and families. Clans are groups of families for which there is evidence of common ancestry. Families are grouped by their catalytic type.he first character representing the catalytic type: A.spartic; C.ysteine; G.lutamic acid; M.etallo; S.erine; T.hreonine; and U.nknown. A clan that contains families of more than one type is described as being of type P. The serine.hreonine and cysteine peptidases utilise the catalytic part of an amino acid as a nucleophile and form an acyl intermediate - these peptidases can also readily act as transferases. In the case of aspartic.lutamic and metallopeptidases.he nucleophile is an activated water molecule. Aspartic endopeptidases () of vertebrate.ungal and retroviral origin have been characterised .Aspartate peptidases are so named because Asp residues are the ligands of the activated water molecule in all examples where the catalytic residues have been identified.lthough at least one viral enzyme is believed to have an Asp and an Asn as its catalytic dyad. All or most aspartate peptidases are endopeptidases. These enzymes have been assigned into clans (proteins which are evolutionary related).nd further sub-divided into families.argely on the basis of their tertiary structure.These aspartate proteases all contain a common closed beta barrel structure.hich includes pepsin.athepsin.hymosin.eta-secretase.lasmepsin.lant acid proteases and retroviral proteases .
  IPR009007:Peptidase aspartic, catalytic
The lysosomal degradation of several sphingolipids requires the presence of four small glycoproteins called saposins.enerated by proteolytic processing of a common precursor.rosaposin . Saposins have three conserved disulphide bridges.nd display a 5-helical.losed.olded leaf topology. Other proteins have been shown to have structures that closely resemble saposin.uch as the antimicrobial peptides NK-lysin and granulysin . Some proteins contain saposin-like domains.uch as prophytepsin.n acid protease from plants.nd J3-crystallin.n eye-lens protein from jellyfish.oth of which contain circularly permuted saposin motifs called swaposin . In some saposins and saposin-like domains.ipid-binding can promote conformational changes and oligomerization.The SSF signature in this entry is currently under review. Please be aware that some of the protein hits may be false positives.
  IPR011001:Saposin-like
IPR008139:SapB 
Evalue:-27.1191864077192 
Location:61-138IPR008139:SapB 
Evalue:-25.8860566476932 
Location:313-388IPR008139:SapB 
Evalue:-23.7958800173441 
Location:407-482IPR003119:SapA 
Evalue:-22.4814853668213 
Location:21-54IPR003119:SapA 
Evalue:-20.1870861053467 
Location:491-524IPR008139:SapB 
Evalue:-17.0809219076239 
Location:196-271IPR008373:SAPOSIN 
Evalue:0 
Location:156-181
SequencesProtein: SAP_HUMAN (524 aa)
mRNA: M60258 NM_002778
Local Annotation
Synapse Ontology
Microglias, one kind of glias in CNS, are responsible for removing most of the waste and cellular debris from the CNS
sdb:0267 removing metabolic mass  (Evidence:keywords)
KO assignmentNot mapped to KEGG
Loci Structure (Details)Loci index, Chromosomal location, Length, Possible relational loci clusterExon1: 393 residues, 73246061-73247239Exon2: 38 residues, 73248379-73248487Exon3: 29 residues, 73248793-73248874Exon4: 54 residues, 73249227-73249385Exon5: 64 residues, 73249476-73249663Exon6: 34 residues, 73250002-73250098Exon7: 47 residues, 73251638-73251775Exon8: 21 residues, 73255598-73255656Exon9: 50 residues, 73257776-73257920Exon10: 69 residues, 73258639-73258840Exon11: 44 residues, 73260888-73261014Exon12: 27 residues, 73261608-73261683Exon13: 46 residues, 73264134-73264268Exon14: 15 residues, 73280944-73280984Exon15: 2 residues, -Jump to SAP_HUMANExon1: 393 residues, 73246063-73247239Exon2: 38 residues, 73248379-73248487Exon3: 29 residues, 73248793-73248874Exon4: 54 residues, 73249227-73249385Exon5: 64 residues, 73249476-73249663Exon6: 34 residues, 73250002-73250098Exon7: 46 residues, 73251638-73251770Exon8: 21 residues, 73255599-73255656Exon9: 50 residues, 73257776-73257920Exon10: 69 residues, 73258639-73258840Exon11: 44 residues, 73260888-73261014Exon12: 27 residues, 73261608-73261683Exon13: 46 residues, 73264134-73264268Exon14: 25 residues, 73280944-73281015Exon15: 2 residues, -Jump to SAP_HUMAN  
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