Beta-eliminative cleavage of 3-ketocerebroside and 3-ketosphingomyelin

Formation of keto-type ceramides in palmoplantar keratoderma based on biallelic KDSR mutations in patients

Functional skin barrier requires sphingolipid homeostasis. 3-ketodihydrosphingosine reductase or KDSR is a key enzyme of sphingolipid anabolism catalyzing the reduction of 3-ketodihydrosphingosine to sphinganine. Biallelic mutations in the KDSR gene may cause erythrokeratoderma variabilis et progressive-4, later specified as PERIOPTER syndrome, emphasizing a characteristic periorifical and ptychotropic erythrokeratoderma. We report another patient with compound heterozygous mutations in KDSR, born with generalized harlequin ichthyosis, which progressed into palmoplantar keratoderma. To determine whether patient-associated KDSR mutations lead to KDSR substrate accumulation and/or unrecognized sphingolipid downstream products in stratum corneum we analyzed lipids of this and previously published patients with non-identical biallelic mutations in KDSR. In stratum corneum of both patients we identified hitherto unobserved skin ceramides with an unusual keto-type sphingoid base in lesional and non-lesional areas, which accounted for up to 10% of the measured ceramide species. Furthermore, an overall shorter mean chain length of free and bound sphingoid bases was observed-shorter mean chain length of free sphingoid bases was also observed in lesional psoriasis vulgaris SC, but not generally in lesional atopic dermatitis SC. Formation of keto-type ceramides is probably due to a bottle neck in metabolic flux through KDSR and a bypass by ceramide synthases, which highlights the importance of tight intermediate regulation during sphingolipid anabolism and reveals substrate deprivation as potential therapy.

The polar-lipid composition of the sphingolipid-producing bacterium Flectobacillus major

Polar lipids comprise about 90% of the total chloroform-methanol extractable lipids of the Gram-negative, fresh-water, ring-forming bacterium Flectobacillus major FM and consist of at least 10 constituents. These are aminophosphosphingolipids, 2-N-(2'-D-hydroxy-13'-methyltetradecanoyl)-15-methyl-4(E)-hexad ecasph ingenyl-1-phosphoethanolamine (36.8% of the total polar lipids) and its 2'-deoxy derivative (3.7%); sulfonic-acid analogues of ceramide, 2-D-(2'-D-hydroxy-13'-methyltetradecanoyl)amino-3-D-hydroxy-15-met hyl hexadecane-1-sulfonic acid (18.1%) and its 2'-deoxy derivative (3. 5%); a lipoamino acid, N-[3-D-(15'-methylhexadecanoyloxy)-15-methylhexadecanoyl]-gl ycine (3. 7%); a lipodipeptide, N-¿N'-[3"-D-(15"'-methylhexadecanoyloxy)-15"-methylhexadecanoyl ]glycy l¿-L-serine (7.8%); 1,2-diacyl-sn-glycero-3-phosphoethanolamine (7. 7%), 1,2-diacyl-3-alpha-D-galactopyranosyl-sn-glycerol (2.9%); ceramide phospho-myo-inositol (4.9%), and a previously described unusual glycosphingolipid, 7-deoxy-7-amino-D-manno-heptulosonopyranosyl (1-hydroxycarbonyl-6-deoxy-6-amino-alpha-D-mannopyranosyl) ceramide (10.9%); the last two lipids contain only 15-methyl-4(E)-hexadecasphingenine as a long-chain base. The sole structural type of amide-bound fatty acids in the sphingolipids, including the sulfonic-acid analogues, is iso-15:0, either non-hydroxylated or hydroxylated at 2-C, whereas 15-methylhexadecanoic acid is the major ester-bound fatty acid in the remaining lipids.

A novel glycosphingolipid from gram-negative aquatic bacteria

The chloroform-methanol extractable lipids of the Gram-negative fresh-water bacteria Arcocella aquatica NO-502 and Flectobacillus major FM were found to contain an unusual ninhydrin-positive glycolipid. It was purified by two-stage silica gel-column chromatography. By the use of IR and (1)H-NMR spectroscopy, mass spectrometry and chemical-degradation experiment, the lipid was established to be 1-O-monoglycosyl ceramide, the carbohydrate moiety of which was the alpha-pyranose-ring form of 7-desoxy-7-amino-D-manno-heptulosonic acid, or 1-hydroxycarbonyl-6-deoxy-6-amino-alpha-D-mannopyranose. The ceramide portion consisted mainly (by 95% in the A. aquatica glycolipid and 80% in the F. major glycolipid) of 2-N-(2'-D-hydroxy-13'-methyltetradecanoyl)-15-methyl-4(E)-hexad ecasph ingenine. The minor molecular species differed from the major one only in fatty acid structure. The glycolipid accounted for 8 and 11% of the total lipids extracted from A. aquatica NO-502 and F. major FM cells, respectively.

Specific tritium labeling of glucosyl- and galactosylceramides at the 6-position of the carbohydrate moiety using CrO3-graphite

A new procedure for introducing tritium into the carbohydrate portions of glucosyl- and galactosylceramides was developed using a new catalyst, CrO3-graphite, which specifically oxidizes the primary alcohol group to the aldehyde. About 10% of the glycolipid was converted to the aldehyde and the aldehyde produced was then reduced back to the original form with KB3H4. After methanolysis, more than 96.7% of the radioactivities of [3H]glucosyl- and [3H]galactosylceramides were found to be located in the carbohydrate portions, and the specific activities of the [3H]galactosyl- and [3H]glucosylceramides were 2.08 to 4.30 X 10(4) cpm/nmol, which could be increased greatly by purifying the aldehydes and reducing them with KB3H4. In addition, beta-galactosidase activity was successfully determined with [3H]galactosylceramide as the enzyme substrate; the Km was 18.73 mM and the Vmax was 11.63 nmol/mg/h, indicating that no significant structural modification occurs during the oxidation.