Publications

• The reverse activity of human acid ceramidase.

  Okino N., He X., Gatt S., Sandhoff K., Ito M., Schuchman E.H.

  An overexpression system was recently developed to produce and purify recombinant, human acid ceramidase. In addition to ceramide hydrolysis, the purified enzyme was able to catalyze ceramide synthesis using [14C]lauric acid and sphingosine as substrates. Herein we report detailed characterization ... >> More

  An overexpression system was recently developed to produce and purify recombinant, human acid ceramidase. In addition to ceramide hydrolysis, the purified enzyme was able to catalyze ceramide synthesis using [14C]lauric acid and sphingosine as substrates. Herein we report detailed characterization of this acid ceramidase-associated "reverse activity" and provide evidence that this reaction occurs in situ as well as in vitro. The pH optimum of the reverse reaction was approximately 5.5, as compared with approximately 4.5 for the hydrolysis reaction. Non-ionic detergents and zinc cations inhibited the activity, whereas most other cations were stimulatory. Of note, sphingomyelin also was very inhibitory toward this reaction, whereas the anionic lipids, phosphatidic acid and phosphatidylserine, were stimulatory. Of various sphingosine stereoisomers tested in the reverse reaction, only the natural, D-erythro form could efficiently serve as a substrate. Using D-erythro-sphingosine and lauric acid as substrates, the reaction followed normal Michaelis-Menten kinetics. The Km and Vmax values toward sphingosine were 23.75 microM and 208.3 pmol/microg/h, respectively, whereas for lauric acid they were 73.76 microM and 232.5 pmol/microg/h, respectively. Importantly, the reverse activity was reduced in cell lysates from a Farber disease patient to the same extent as the acid ceramidase activity. Furthermore, when 12-(N-methyl-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)) (NBD)-conjugated lauric acid and sphingosine were added to cultured lymphoblasts from a Farber disease patient in the presence of fumonisin B (1), the conversion to NBD-ceramide was reduced approximately 30% when compared with normal cells. These data provide important new information on human acid ceramidase and further document its central role in sphingolipid metabolism. << Less

  J. Biol. Chem. 278:29948-29953(2003) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.

• Purification and characterization of recombinant, human acid ceramidase. Catalytic reactions and interactions with acid sphingomyelinase.

  He X., Okino N., Dhami R., Dagan A., Gatt S., Schulze H., Sandhoff K., Schuchman E.H.

  Human acid ceramidase was overexpressed in Chinese hamster ovary cells by amplification of the transfected, full-length cDNA. The majority of the overexpressed enzyme was secreted into the culture media and purified to apparent homogeneity. The purified protein contained the same 13-(alpha) and 40 ... >> More

  Human acid ceramidase was overexpressed in Chinese hamster ovary cells by amplification of the transfected, full-length cDNA. The majority of the overexpressed enzyme was secreted into the culture media and purified to apparent homogeneity. The purified protein contained the same 13-(alpha) and 40 (beta)-kDa subunits as human acid ceramidase from natural sources, had an acidic pH optimum (4.5), and followed normal Michaelis-Menten kinetics using 14C- and BODIPY-labeled C12-ceramide as substrates. Deglycosylation studies showed that the recombinant enzyme contained mostly "high mannose" type oligosaccharides and that two distinct beta-subunits were present. Amino acid sequencing of these subunit polypeptides revealed a single N terminus, suggesting that the approximately 2-4-kDa molecular mass difference was likely due to C-terminal processing. The purified enzyme also catalyzed ceramide synthesis in vitro using 14C-labeled C12 fatty acid and sphingosine as substrates. Surprisingly, we found that media from the overexpressing hamster cells had increased acid sphingomyelinase activity and that this activity could be co-precipitated with acid ceramidase using anti-ceramidase antibodies. Overexpression of acid ceramidase in normal human skin fibroblasts also led to enhanced acid sphingomyelinase secretion, but this was not observed in Niemann-Pick disease cells. RNA studies showed that this increased activity was not due to overexpression of the endogenous acid sphingomyelinase gene. Uptake studies using mouse macrophages revealed rapid internalization of the acid ceramidase activity from the hamster cell media but not acid sphingomyelinase. These studies provide new insights into acid ceramidase and the related lipid hydrolase, acid sphingomyelinase. << Less

  J. Biol. Chem. 278:32978-32986(2003) [PubMed] [EuropePMC]

• Purification, characterization, and biosynthesis of human acid ceramidase.

  Bernardo K., Hurwitz R., Zenk T., Desnick R.J., Ferlinz K., Schuchman E.H., Sandhoff K.

  Acid ceramidase (N-acylsphingosine deacylase, EC 3.5.1.23) is the lysosomal enzyme catalyzing the hydrolysis of ceramide to sphingosine and free fatty acid. Its inherited deficiency causes ceramide accumulation in Farber's disease. The enzyme was purified to apparent homogeneity from human urine b ... >> More

  Acid ceramidase (N-acylsphingosine deacylase, EC 3.5.1.23) is the lysosomal enzyme catalyzing the hydrolysis of ceramide to sphingosine and free fatty acid. Its inherited deficiency causes ceramide accumulation in Farber's disease. The enzyme was purified to apparent homogeneity from human urine by sequential chromatography on octyl-Sepharose, concanavalin A-Sepharose, blue-Sepharose, and DEAE-cellulose. The final preparation, which was enriched approximately 4450-fold over the starting material, resulted in a polypeptide of approximately 50 kDa and could be reduced into two subunits of approximately 13 (alpha) and approximately 40 (beta) kDa. Treatment of the purified enzyme with endoglycosidase H or peptido-N-glycanase F reduced the molecular mass of the beta subunit to approximately 30-35 and approximately 27 kDa, respectively. In contrast, the molecular mass of the alpha subunit was unchanged. The purified enzyme had an apparent Km of 149 microM and a Vmax of 136 nmol/mg/h using N-lauroylsphingosine as substrate. Polyclonal antibodies were raised against the purified urinary enzyme and used to investigate the biosynthesis of acid ceramidase. Immunoprecipitation studies on metabolically labeled skin fibroblasts indicated that both subunits arose from a single precursor of approximately 55 kDa. A minor portion of newly synthesized acid ceramidase was secreted into the medium as a monomeric 47-kDa protein, indicating that generation of the mature heterodimeric enzyme occurred in endosomal and/or lysosomal compartments. << Less

  J. Biol. Chem. 270:11098-11102(1995) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.

• Purification and characterization of a neutral ceramidase from mouse liver. A single protein catalyzes the reversible reaction in which ceramide is both hydrolyzed and synthesized.

  Tani M., Okino N., Mitsutake S., Tanigawa T., Izu H., Ito M.

  We report here a novel ceramidase that was purified more than 150, 000-fold from the membrane fraction of mouse liver. The enzyme was a monomeric polypeptide having a molecular mass of 94 kDa and was highly glycosylated with N-glycans. The amino acid sequence of a fragment obtained from the purifi ... >> More

  We report here a novel ceramidase that was purified more than 150, 000-fold from the membrane fraction of mouse liver. The enzyme was a monomeric polypeptide having a molecular mass of 94 kDa and was highly glycosylated with N-glycans. The amino acid sequence of a fragment obtained from the purified enzyme was homologous to those deduced from the genes encoding an alkaline ceramidase of Pseudomonas aeruginosa and a hypotheical protein of the slime mold Dictyostelium discoideum. However, no significant sequence similarities were found in other known functional proteins including acid ceramidases of humans and mice. The enzyme hydrolyzed various N-acylsphingosines but not galactosylceramide, sulfatide, GM1a, or sphingomyelin. The enzyme exhibited the highest activity around pH 7.5 and was thus identified as a type of neutral ceramidase. The apparent K(m) and V(max) values for C12-4-nitrobenzo-2-oxa-1, 3-diazole-ceramide and C16-(14)C-ceramide were 22.3 microM and 29.1 micromol/min/mg and 72.4 microM and 3.6 micromol/min/mg, respectively. This study also clearly demonstrated that the purified 94-kDa ceramidase catalyzed the condensation of fatty acid to sphingosine to generate ceramide, but did not catalyze acyl-CoA-dependent acyl-transfer reaction. << Less

  J. Biol. Chem. 275:3462-3468(2000) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.

• Identification of a novel amidase motif in neutral ceramidase.

  Galadari S., Wu B.X., Mao C., Roddy P., El Bawab S., Hannun Y.A.

  Neutral CDases (ceramidases) are newly identified enzymes with important roles in cell regulation, but little is known about their catalytic mechanisms. In the present study the full-length human neutral CDase was cloned and expressed in the yeast double-knockout strain Dypc1Dydc1, which lacks the ... >> More

  Neutral CDases (ceramidases) are newly identified enzymes with important roles in cell regulation, but little is known about their catalytic mechanisms. In the present study the full-length human neutral CDase was cloned and expressed in the yeast double-knockout strain Dypc1Dydc1, which lacks the yeast CDases YPC1p and YDC1p. Biochemical characterization of the human neutral CDase showed that the enzyme exhibited classical Michaelis-Menten kinetics, with an optimum activity at pH 7.5. Activity was enhanced by Na+ and Ca2+. Mg2+ and Mn2+ were somewhat stimulatory, but Zn2+, Cu2+ and Fe2+ inhibited the enzyme. Dithiothreitol and 2-mercaptoethanol dose-dependently inhibited neutral CDase. In order to identify which amino acids were involved in the catalytic action of neutral CDase, the purified enzyme was subjected to chemical modifications. It was observed that the serine residue modifier di-isopropyl fluorophosphate dose-dependently inhibited activity, implicating a serine residue in the catalytic action. From an alignment of the sequences of the neutral CDases from different species, all conserved serine residues were selected for site-directed mutagenesis. Of the six aligned serine residues that were mutated to alanine, only the S354A mutant lost its activity totally. Ser354 falls within a very highly conserved hexapeptide sequence GDVSPN, which itself was in the middle of a larger conserved sequence, namely NXGDVSPNXXGP/XXC. Moreover, mutations of Asp352 and Cys362 in the consensus sequence to alanine resulted in loss of activity of neutral CDase. Hence the present study identified a novel amidase sequence containing a critical serine residue that may function as a nucleophile in the hydrolytic attack on the amide bond present in ceramide. << Less

  Biochem. J. 393:687-695(2006) [PubMed] [EuropePMC]

• Substrate specificity, membrane topology, and activity regulation of human alkaline ceramidase 2 (ACER2).

  Sun W., Jin J., Xu R., Hu W., Szulc Z.M., Bielawski J., Obeid L.M., Mao C.

  Human alkaline ceramidase 2 (ACER2) plays an important role in cellular responses by regulating the hydrolysis of ceramides in cells. Here we report its biochemical characterization, membrane topology, and activity regulation. Recombinant ACER2 was expressed in yeast mutant cells (Deltaypc1Deltayd ... >> More

  Human alkaline ceramidase 2 (ACER2) plays an important role in cellular responses by regulating the hydrolysis of ceramides in cells. Here we report its biochemical characterization, membrane topology, and activity regulation. Recombinant ACER2 was expressed in yeast mutant cells (Deltaypc1Deltaydc1) that lack endogenous ceramidase activity, and microsomes from ACER2-expressiong yeast cells were used to biochemically characterize ACER2. ACER2 catalyzed the hydrolysis of various ceramides and followed Michaelis-Menten kinetics. ACER2 required Ca(2+) for both its in vitro and cellular activities. ACER2 has 7 putative transmembrane domains, and its amino (N) and carboxyl (C) termini were found to be oriented in the lumen of the Golgi complex and cytosol, respectively. ACER2 mutant (ACER2DeltaN36) lacking the N-terminal tail (the first 36 amino acid residues) exhibited undetectable activity and was mislocalized to the endoplasmic reticulum, suggesting that the N-terminal tail is necessary for both ACER2 activity and Golgi localization. ACER2 mutant (ACER2DeltaN13) lacking the first 13 residues was also mislocalized to the endoplasmic reticulum although it retained ceramidase activity. Overexpression of ACER2, ACER2DeltaN13, but not ACER2DeltaN36 increased the release of sphingosine 1-phosphate from cells, suggesting that its mislocalization does not affect the ability of ACER2 to regulate sphingosine 1-phosphate secretion. However, overexpression of ACER2 but not ACER2DeltaN13 or ACER2DeltaN36 inhibited the glycosylation of integrin beta1 subunit and Lamp1, suggesting that its mistargeting abolishes the ability of ACER2 to regulation protein glycosylation. These data suggest that ACER2 has broad substrate specificity and requires Ca(2+) for its activity and that ACER2 has the cytosolic C terminus and luminal N terminus, which are essential for its activity, correct cellular localization, and regulation for protein glycosylation. << Less

  J. Biol. Chem. 285:8995-9007(2010) [PubMed] [EuropePMC]

  This publication is cited by 7 other entries.

• Human acid ceramidase: processing, glycosylation, and lysosomal targeting.

  Ferlinz K., Kopal G., Bernardo K., Linke T., Bar J., Breiden B., Neumann U., Lang F., Schuchman E.H., Sandhoff K.

  The biosynthesis of human acid ceramidase (hAC) starts with the expression of a single precursor polypeptide of approximately 53-55 kDa, which is subsequently processed to the mature, heterodimeric enzyme (40 + 13 kDa) in the endosomes/lysosomes. Secretion of hAC by either fibroblasts or acid cera ... >> More

  The biosynthesis of human acid ceramidase (hAC) starts with the expression of a single precursor polypeptide of approximately 53-55 kDa, which is subsequently processed to the mature, heterodimeric enzyme (40 + 13 kDa) in the endosomes/lysosomes. Secretion of hAC by either fibroblasts or acid ceramidase cDNA-transfected COS cells is extraordinarily low. Both lysosomal targeting and endocytosis critically depend on a functional mannose 6-phosphate receptor as judged by the following criteria: (i) hAC-precursor secretion by NH(4)Cl-treated fibroblasts and I-cell disease fibroblasts, (ii) inhibition of the formation of mature heterodimeric hAC in NH(4)Cl-treated fibroblasts or in I-cell disease fibroblasts, and (iii) blocked endocytosis of hAC precursor by mannose 6-phosphate receptor-deficient fibroblasts or the addition of mannose 6-phosphate. The influence of the six individual potential N-glycosylation sites of human acid ceramidase on targeting, processing, and catalytic activity was determined by site-directed mutagenesis. Five glycosylation sites (sites 1-5 from the N terminus) are used. The elimination of sites 2, 4, and 6 has no influence on lysosomal processing or enzymatic activity of recombinant ceramidase. The removal of sites 1, 3, and 5 inhibits the formation of the heterodimeric enzyme form. None of the mutant ceramidases gave rise to an increased rate of secretion, suggesting that lysosomal targeting does not depend on one single carbohydrate chain. << Less

  J. Biol. Chem. 276:35352-35360(2001) [PubMed] [EuropePMC]

• Cloning and characterization of a mouse endoplasmic reticulum alkaline ceramidase: an enzyme that preferentially regulates metabolism of very long chain ceramides.

  Mao C., Xu R., Szulc Z.M., Bielawski J., Becker K.P., Bielawska A., Galadari S.H., Hu W., Obeid L.M.

  Ceramidases deacylate ceramides, important intermediates in the metabolic pathway of sphingolipids. In this study, we report the cloning and characterization of a novel mouse alkaline ceramidase (maCER1) with a highly restricted substrate specificity. maCER1 consists of 287 amino acids, and it has ... >> More

  Ceramidases deacylate ceramides, important intermediates in the metabolic pathway of sphingolipids. In this study, we report the cloning and characterization of a novel mouse alkaline ceramidase (maCER1) with a highly restricted substrate specificity. maCER1 consists of 287 amino acids, and it has a 28 and 32% identity to the Saccharomyces alkaline ceramidases (YPC1p and YDC1p) and the human alkaline phytoceramidase, respectively. Reverse transcriptase-PCR analysis demonstrated that maCER1 was predominantly expressed in skin. maCER1 was localized to the endoplasmic reticulum as revealed by immunocytochemistry. In vitro biochemical characterization determined that maCER1 hydrolyzed D-erythro-ceramide exclusively but not D-erythro-dihydroceramide or D-ribo-phytoceramide. Similar to other alkaline ceramidases, maCER1 had an alkaline pH optimum of 8.0, and it was activated by Ca2+ but inhibited by Zn2+,Cu2+, and Mn2+. maCER1 was also inhibited by sphingosine, one of its products. Metabolic labeling studies showed that overexpression of maCER1 caused a decrease in the incorporation of radiolabeled dihydrosphingosine into ceramide and complex sphingolipids but led to a concomitant increase in sphingosine-1-P (S1P) in HeLa cells. Mass measurement showed that overexpression of maCER1 selectively lowered the cellular levels of D-erythro-C24:1-ceramide, but not other ceramide species and caused an increase in the levels of S1P. Taken together, these data suggest that maCER1 is a novel alkaline ceramidase with a stringent substrate specificity and that maCER1 is selectively expressed in skin and may have a role in regulating the levels of bioactive lipids ceramide and S1P, as well as complex sphingolipids. << Less

  J. Biol. Chem. 278:31184-31191(2003) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Molecular characterization of N-acylethanolamine-hydrolyzing acid amidase, a novel member of the choloylglycine hydrolase family with structural and functional similarity to acid ceramidase.

  Tsuboi K., Sun Y.-X., Okamoto Y., Araki N., Tonai T., Ueda N.

  Bioactive N-acylethanolamines, including anandamide (an endocannabinoid) and N-palmitoylethanolamine (an anti-inflammatory and neuroprotective substance), are hydrolyzed to fatty acids and ethanolamine by fatty acid amide hydrolase. Moreover, we found another amidohydrolase catalyzing the same rea ... >> More

  Bioactive N-acylethanolamines, including anandamide (an endocannabinoid) and N-palmitoylethanolamine (an anti-inflammatory and neuroprotective substance), are hydrolyzed to fatty acids and ethanolamine by fatty acid amide hydrolase. Moreover, we found another amidohydrolase catalyzing the same reaction only at acidic pH, and we purified it from rat lung (Ueda, N., Yamanaka, K., and Yamamoto, S. (2001) J. Biol. Chem. 276, 35552-35557). Here we report complementary DNA cloning and functional expression of the enzyme termed "N-acylethanolamine-hydrolyzing acid amidase (NAAA)" from human, rat, and mouse. The deduced primary structures revealed that NAAA had no homology to fatty acid amide hydrolase but belonged to the choloylglycine hydrolase family. Human NAAA was essentially identical to a gene product that had been noted to resemble acid ceramidase but lacked ceramide hydrolyzing activity. The recombinant human NAAA overexpressed in HEK293 cells hydrolyzed various N-acylethanolamines with N-palmitoylethanolamine as the most reactive substrate. Most interestingly, a very low ceramide hydrolyzing activity was also detected with NAAA, and N-lauroylethanolamine hydrolyzing activity was observed with acid ceramidase. By the use of tunicamycin and endoglycosidase, NAAA was found to be a glycoprotein. Furthermore, the enzyme was proteolytically processed to a shorter form at pH 4.5 but not at pH 7.4. Expression analysis of a green fluorescent protein-NAAA fusion protein showed a lysosome-like distribution in HEK293 cells. The organ distribution of the messenger RNA in rats revealed its wide distribution with the highest expression in lung. These results demonstrated that NAAA is a novel N-acylethanolamine-hydrolyzing enzyme that shows structural and functional similarity to acid ceramidase. << Less

  J. Biol. Chem. 280:11082-11092(2005) [PubMed] [EuropePMC]

  This publication is cited by 4 other entries.