Saposin protein domain

Saposin protein domain
Identifiers
Symbol SapA
Pfam PF02199
InterPro IPR003119
PROSITE PDOC51110
Saposin-like type B, region 1
Saposin C 2qyp.png
Crystal structure of human saposin C dimer in an open conformation.[1]
Identifiers
Symbol SapB_1
Pfam PF05184
InterPro IPR007856
PROSITE PDOC50015
Identifiers
Symbol SapB_2
Pfam PF03489
InterPro IPR008138
PROSITE PDOC50015
SCOP 1nkl
OPM family 83
OPM protein 1sn6

Saposins are small lysosomal proteins that serve as activators of various lysosomal lipid-degrading enzymes.[2] They probably act by isolating the lipid substrate from the membrane surroundings, thus making it more accessible to the soluble degradative enzymes. All mammalian saposins are synthesized as a single precursor molecule (prosaposin) which contains four Saposin-B domains, yielding the active saposins after proteolytic cleavage, and two Saposin-A domains that are removed in the activation reaction. The Saposin-B domains also occur in other proteins, many of them active in the lysis of membranes.[3][4]

Contents

Domain organization

Below is a schematic diagram of the 1D structure of the prosaposin protein depicting the N- and C-terminal SapA domains and the four SapB1 and four SapB2 domains. Proteolytic cleavage of the proprotein occurs in the grey regions. Adjacent pairs of SapB1 and SapB2 domains remain connected after proteolytic processing of prosaposin and each pair comprises one of the mature saponin A-D proteins.

Prosaposin schematic.png

Human proteins containing this domain

References

  1. ^ PDB 2qyp, Rossmann 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. PMID 18462685. 
  2. ^ Munford RS, Sheppard PO, O Hara PJ (1995). "Saposin-like proteins (SAPLIP) carry out diverse functions on a common backbone structure". J. Lipid Res. 36 (8): 1653–1663. PMID 7595087. 
  3. ^ 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. PMC 2142785. PMID 8003971. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2142785. 
  4. ^ 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. PMID 8868085. 

Further reading

  • Ponting CP, Russell RB (May 1995). "Swaposins: circular permutations within genes encoding saposin homologues". Trends in Biochemical Sciences 20 (5): 179–80. doi:10.1016/S0968-0004(00)89003-9. PMID 7610480. 

External links

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