Ceramidases

Farber s disease Ceramidase Acyl-i-Sphingosine Ceramide Hoarseness, dermatitis, skeletal deformation, mental retardation fatal in early life. 

Farber s disease is a rare disorder caused by deficiency of acid ceramidase and is associated with the accumulation of ceramide in subcutaneous tissues, joints, kidney, lung and neurons. Gangliosides also accumulate. 

Farber s disease (lipogranulomatosis) Acid ceramidase Ceramide... 

Auge, N., Nikolova-Karakashian, M., Carpentier, S., Parthasarathy, S., Negre-Salvayre, A., Salvayre, R., Merrill, A.H. Jr, Levade, T, 1999, Role of sphingosine 1-phosphate in the mitogenesis induced by oxidized LDL in smooth muscle cells via activation of sphingomyelinase, ceramidase, and sphingosine kinase, J. Biol. Chem. 274 21533-21538. 

Abbreviations CL, cardioUpin CDase, ceramidase Cer, Ceramide dhCer, dihydroceramide FBI, fumonisin Bl PA, phosphatidic acid PS, phosphatidylserine phytoCer, phytoceramide SPH, sphingosine SIP, sphingosine-1-phosphate. 

Figure 1. Scheme of sphingolipid metabolism and the central role of ceramide and ceramidases. 

Ceramidases are enzymes that cleave the N-acyl linkage of Cer into SPH and free fatty acid. They are an emerging class of enzymes composed of multiple isoforms. Historically, these isoforms have been classified as acid, neutral or alkaline, based on the pH optimum of their activities although some isoforms show activity in a broad range. With the recent cloning of several isoforms from yeast, bacteria, and mammals, a genetical distinction and classification of these enzymes can now be employed. 

Very recently, two yeast (5. cerevisiae) alkaline ceramidases, phytoceramidase (YPClp) and dihydroceramidase (YDClp), were cloned and partially characterized by Mao et al (2000a, b). YPClp was cloned as a high copy suppressor of the growth inhibition by FBI as it has fumoitisin resistant ceramide synthase activity. The second alkaline ceramidase, YDClp was identified by sequence homology to YPClp. 

Figure 2. Alignment of the human mitochondrial ceramidase to homologous ceramidases from various organisms. Sequences of ceramidases were aligned using ClustalW algorithm of the Mac Vector program. Amino acids identical are shaded in grey and consensus residues are shown under the alignment. Amino acids of the same group are shaded in white.

YPClp and YDClp have different substrate specificity such that YPClp prefers phytoceramide (phytoCer) over dihydroceramide (dhCer) whereas YDClp prefers dhCer over phytoCer, however, neither enzyme uses the most common mammalian type ceramide having a 4-5 trans double bond on the sphingoid base as substrate. Both enzymes have a narrow pH optimum of 9.4-10, hence, are classified as alkaline ceramidases. Calcium ions activate but are not absolutely required for the activities of both enzymes. and inhibit the activities of both enzymes. None of the sphingoid bases inhibit the activities of YPC Ip and YDClp. 

A database search reveals that YPClp and YDClp are not homologous to any proteins with known functions, but are homologous to putative proteins from Arabidoposis, C. elegans, peptides deduced from EST sequences of human, mouse, pig, zebra fish, and human genomic sequences. A human homologue has been identified and its cDNA has been cloned. Preliminary results show that this human homologue is also an alkaline ceramidase that selectively hydrolyzes phytoCer. 

Figure 3. Scheme of ceramidases regulation in agonist mediated cell responses. 

The physiological roles of the yeast (and their human homologues) alkaline ceramidases are yet to be established. Since these enzymes regulate a series of bioactive lipids such as ceramide, sphingosine, and sphingosine-1-P, we predict that they have an important role in cell regulatory events. 

Figure 4. Proposed role for ceramidases as "switches" between cell death and cell proliferation.

Hannun, Y.A., 1996, (lS,2R)-D-erythro-2-(N-myristoylamino)-l-phenyl-l-propanol as an inhibitor of ceramidase. J. Biol. Chem. 271 12646-12654. 

Chen, W.W., Moser, A.B., and Moser, H.W., 1981, Role oflysosomal add ceramidase in the metabohsm of ceramide in human skin fibroblasts. Arch. Biochem. Biophys. 208 444-455. 

Coroneos, E., Martinez, M., McKenna, S. and Kester, M., 1995, Differential regulation of sphingomyelinase and ceramidase activities by growth factors and cytokines. Implications for cellular proliferation and differentiation./.B/oZ.Clrem. 270 23305-23309. 

El Bawab, S., Bielawska, A., Hannun, Y.A., 1999, Purification and characterization ofa membrane-bound non-lysosomal ceramidase from rat brain. J. Biol.Chem. 274 27948-27955. 

Biochemical characterization of the reverse activity of rat brain ceramidase A CoA-independent and fumonisin B1 insensitive ceramide synthase. J. Biol. Chem. published February 8, 2001 as 10.1074/jbc.M009331200. 

Kita, K., Okino, N., and Ito, M., 2000, Reverse hydrolysis reaction of a recombinant alkaline ceramidase of Pseudomonas aeruginosa. B/oc/t/m. Biophys. Acta. 1485 111-120. 

Koch, J., Gartner, S., li, CM., Quintern, L.E., Bernardo, K., Levran, O., Schnabel, D., Desnick, R.J., Schuchman, E.H., and Sandhoff, K., 1996, Molecular cloning and characterization of a fuU-length complementary DNA encoding human acid ceramidase. Identification ofthe first molecular lesion causing Earber disease. 7. Biol. Chem. 271 33110-33115. 

K., and Schuchman, E.H., 1998, Cloning and characterization ofthe full-length cDNA and genomic sequences encoding murine acid ceramidase. Genomics. 50 267-274. 

Linke, T., Wilkening, G., Sadeghlar,. F, MozcaU, H., Bernardo, K., Schuchman, E., and Sandhoff, K., 2001, Interfacial Regulation of Acid Ceramidase Activity. Stimulation of ceramide degradation by lysosomal lipids and Sphingolipid Activator Proteins. J. Biol. Chem. 276 5760-5768. 

Mao, C., Xu, R., Bielawska, A., and Obeid, L.M., 2000a, Cloning of an alkaline ceramidase from Saccharomyces cerevisiae. An enzyme with reverse (CoA-independent) ceramide synthase achvity. J. Biol. Chem., 275 6876-6884. 

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