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PubMed2006

Biophysics of sphingolipids II. Glycosphingolipids: an assortment of multiple structural information transducers at the membrane surface.

Glycosphingolipids are ubiquitous components of animal cell membranes. They are constituted by the basic structure of ceramide with its hydroxyl group linked to single carbohydrates or oligosaccharide chains of different complexity. The combination of the properties of their hydrocarbon moiety with those derived from the variety and complexity of their hydrophilic polar head groups confers to these lipids an extraordinary capacity for molecular-to-supramolecular transduction across the lateral/transverse planes in biomembranes and beyond. In our opinion, most of the advances made over the last decade on the biophysical behavior of glycosphingolipids can be organized into three related aspects of increasing structural complexity: (1) intrinsic codes: local molecular interactions of glycosphingolipids translated into structural self-organization. (2) Surface topography: projection of molecular shape and miscibility of glycosphingolipids into formation of coexisting membrane domains. (3) Beyond the membrane interface: glycosphingolipid as modulators of structural topology, bilayer recombination and surface biocatalysis.

Biophysical Phenomena↗
PubMed2000

Conformational studies of sphingolipids by NMR spectroscopy. I. Dihydrosphingomyelin.

The conformational features of dihydrosphingomyelin (DHSM), the major phospholipid of human lens membranes, were investigated by 1H and 31P nuclear magnetic resonance spectroscopy. Several postulates emerge from the observed trends: (a) in partially hydrated samples of DHSM in CDCl3 above 13 mM, at which lipid-lipid interactions prevail, the amide proton is mostly involved in intermolecular H-bonds that link neighboring phospholipids through bridging water molecules. In the absence of water, the NH group is involved in an intramolecular H-bond that restricts the mobility of the phosphate group. (b) In the monomeric form of the lipid molecule, the amide proton of the major conformer is bound intramolecularly with one of the anionic and/or ester oxygens of the phosphate group. A minor conformer may also be present in which the NH proton participates in an intramolecular H-bond linking to the OH group of the sphingoid base. (c) Complete hydration leads to an extension of the head group as water molecules bind to the phosphate and NH groups via H-bonds, thus disrupting the intramolecular H-bonds prevalent at low concentrations.

Carbon Isotopes↗
PubMed2004

Identification of the human sphingolipid C4-hydroxylase, hDES2, and its up-regulation during keratinocyte differentiation.

The C4-hydroxylation of dihydrosphingosine or dihydroceramide is a key reaction in the biosynthesis of phytosphingolipids, both in yeasts and in mammalian cells. Mouse DES2 (mDES2) was recently cloned and shown to work as a Delta4-desaturase/C4-hydroxylase, when expressed in yeast cells. Here, we cloned a human homologue of mDES2, hDES2, by homology search utilizing a BLAST program. When expressed in HEK 293 cells, hDES2 exhibited hydroxylase activity for dihydroceramide. Northern blot analyses of hDES2 revealed high expression in skin, intestines, and kidney, sites reportedly possessing high levels of phytosphingolipids. Furthermore, up-regulation of hDES2 mRNA expression and subsequent phytoceramide production were observed during vitamin C/serum-induced differentiation of human keratinocytes. These results suggest that the newly cloned hDES2 plays an essential role in phytosphingolipid synthesis in human skin and other phytosphingolipid-containing tissues.

Amino Acid Motifs↗
PubMed1997

Distribution of sphingosine 1-phosphate, a bioactive sphingolipid, in rat tissues.

Although a growing number of reports on the bioactivities of sphingosine 1-phosphate (Sph-1-P) in various systems have been appearing recently, current evidence for the involvement of Sph-1-P in signal transduction or cellular function(s) consists largely of data on cellular and biochemical effects of exogenous Sph-1-P. In this study, we measured Sph-1-P contents in various rat tissues. When the amount of this sphingoid base was measured by its N-acetylation into [3H]C2-ceramide 1-phosphate with [3H]acetic anhydride, we could detect Sph-1-P in all rat tissues examined. We also got unexpected findings that Sph-1-P exists most abundantly in testis = intestine > spleen (in the order of Sph-1-P abundance when its amounts were adjusted to the phospholipid levels). Our new data on Sph-1-P distribution in rat tissues may imply novel bioactivities for Sph-1-P.

Acetylation↗
PubMed1998

Mg2+ modulates membrane sphingolipid and lipid second messenger levels in vascular smooth muscle cells.

In vitro studies with smooth muscle cells from rat aorta and dog cerebral blood vessels indicate that variation in free Mg2+, within the pathophysiological range of Mg2+ concentrations, found in human serum, causes sustained changes in membrane phospholipids and lipid second messengers. Incorporation of [3H]palmitic acid into phosphatidylcholine (PC) and sphingomyelin (SM) was altered within 15-30 min after modifying the extracellular Mg2+ ion level ([Mg2+]o). Decreased Mg2+ produced a fall in both [3H]SM and [3H]PC over the first 2 h. After an 18-h incubation, the [3H]PC/[3H]SM ratio changed from about 20:1 to about 50:1. Increased [Mg2+]o resulted in a 2- to 3-fold increase in [3H]SM compared to only a small increase in [3H]PC over the same period. There was a reciprocal relationship between [3H]ceramide and [3H]1,2-DAG levels with highest [3H]ceramide and lowest [3H]-1,2-DAG levels seen at lowest [Mg2+]o. The results indicate that a fall in extracellular ionized Mg2+ concentration produces a rapid and sustained decrease in membrane sphingomyelin and a moderate rise in intracellular ceramide. A major effect of lowering [Mg2+]o appears to be a down-regulation of SM synthase. The increased membrane SM content and a concomitant decrease in cell ceramide, in the presence of elevated [Mg2+]o, may be relevant to the apparent protective role of adequate Mg intake on vascular function in humans.

Animals↗