title: Cloning and characterization of the mammalian brain-specific, Mg2+-dependent neutral sphingomyelinase.
abstract: The enzymatic breakdown of sphingomyelin by sphingomyelinases is considered the major source of the second messenger ceramide. Studies on the contribution of the various described acidic and neutral sphingomyelinases to the signaling pool of ceramide have been hampered by the lack of molecular data on the neutral sphingomyelinases (nSMases). We recently identified a mammalian nSMase, an integral membrane protein with remote similarity to bacterial sphingomyelinases. However, its ubiquitous expression pattern is in contrast to previous findings that sphingomyelinase activity is found mainly in brain tissues. By using an improved database search method, combined with phylogenetic analysis, we identified a second mammalian nSMase (nSMase2) with predominant expression in the brain. The sphingomyelinase activity of nSMase2 has a neutral pH optimum, depends on Mg(2+) ions, and is activated by unsaturated fatty acids and phosphatidylserine. Immunofluorescence reveals a neuron-specific punctate perinuclear staining, which colocalizes with a Golgi marker in a number of cell lines. The likely identity of nSMase2 with cca1, a rat protein involved in contact inhibition of 3Y1 fibroblasts, suggests a role for this enzyme in cell cycle arrest. Both mammalian nSMases are members of a superfamily of Mg(2+)-dependent phosphohydrolases, which also contains nucleases, inositol phosphatases, and bacterial toxins.
authors.affiliation: Bioinformatics and Gene Discovery Group, MEMOREC Stoffel GmbH, D-50829 Cologne, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Hofmann
authors.forename: S
authors.initials: S
authors.lastname: Tomiuk
authors.forename: G
authors.initials: G
authors.lastname: Wolff
authors.forename: W
authors.initials: W
authors.lastname: Stoffel
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002453:Cell Cycle / Q000502:physiology; D002478:Cells, Cultured; D003001:Cloning, Molecular; D003260:Contact Inhibition / Q000502:physiology; D018076:DNA, Complementary / Q000235:genetics; D004789:Enzyme Activation; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D006801:Humans; D008274:Magnesium / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D016716:PC12 Cells; D010718:Phosphatidylserines / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry; D051381:Rats; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013108:Sphingomyelin Phosphodiesterase / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D005231:Fatty Acids, Unsaturated; D009419:Nerve Tissue Proteins; D010718:Phosphatidylserines; D020033:Protein Isoforms; C491484:SMPD3 protein, human; C491483:Smpd3 protein, mouse; C107180:Smpd3 protein, rat; D013108:Sphingomyelin Phosphodiesterase; D008274:Magnesium