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Pathways for ceramide synthesis

This communication describes the pathway for the biosynthesis of unique gangliosides, ..

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There are three major pathways of ceramide generation

When the retinoic acid-responsive LAN-5 or SMS-KCNR cells were exposed to 10μ ATRA for 6–7 days (), we observed a marked increase (2.7–2.9-fold, PP=0.198) increase in GD2 synthase activity, and only small changes in GD3 synthase activity (1.2–1.4, P=0.161). Thus, in both LAN-5 and SMS-KCNR cells, increased expression of complex gangliosides downstream of GD1b sythase was associated with a significant (over two-fold) increase in GD1b synthase activity. In contrast, in SMS-KCN cells, the cell line that was unresponsive to ATRA treatment, GD1b synthase activity was only slightly increased (1.5-fold) in ATRA-treated vs control cells.

Ganglioside biosynthesis in mouse embryos: Sialyltransferase IV and the asialo pathway

Ganglioside synthases are glycosyltransferases involved in the biosynthesis of glycoconjugates. A number of ganglioside synthase genes have been cloned and characterized. They are classified into different families of glycosyl-transferases based on similarities of their amino acid sequences. Tissue-specific expression of these genes has been analyzed by hybridization using cDNA fragments. Enzymatic characterization with the expressed recombinant enzymes showed these enzymes differ in their donor and acceptor substrate specificities and other biochemical parameters. In vitro enzymatic analysis also showed that one linkage can be synthesized by multiple enzymes and one enzyme may be responsible for synthesis of multiple gangliosides. Following the cloning of the ganglioside synthase genes, the promoters of the key synthase genes in the ganglioside biosynthetic pathway have been cloned and analyzed. All of thd promoters are TATA-less, lacking a CCAAT box but containing GC-rich boxes, characteristic of the house-keeping genes, although transcription of ganglioside synthase genes is subject to complex developmental and tissue-specific regulation. A set of cis-acting elements and transcription factors, including Sp1, AP2, and CREB, function in the proximal promoters, Negative-regulatory regions have also been defined in most of the promoters. We present here an overview of these genes and their transcriptional regulation.

Important dates in the history of lipids ..

Glycosylation pathways in the biosynthesis of gangliosides in melanoma and neuroblastoma cells: relative glycosyltransferase levels determine ganglioside patterns.

Individual gangliosides were identified using a human brain ganglioside standard or 14C-labelled rat brain gangliosides. The area under the peak generated by each ganglioside band was integrated after the plates/films were scanned (Microtek ScanMaker 5), and the relative percentage was calculated. To categorise individual ganglioside species, we used a previously established classification scheme based on biosynthetic pathways (). Structurally complex molecules downstream of GD1b/GM1a synthase (β-1,3-galactosyltransferase) were designated complex ‘a’ gangliosides (CaG: GM1a, GD1a and GT1a) and complex ‘b’ gangliosides (CbG: GD1b, GT1b and GQ1b), respectively.

The final part of this eBook (Chapters 12 to 14) is devoted to describing tools used to explore Sialobiology, and provides a great example of the interplay between biology and chemistry that has characterized the study of sialic acid since its origins. Magesh and Ando (Chapter 12) not only describe classical sialic acid synthetic methods, but also provide several strategies used for the design of sialylmimetics and their potential development as sialo-pharmaceuticals to treat human diseases. In Chapter 13 Galuska summarizes the various methods used to detect and analyze sialic acid and polysialic acid, and outlines the advantages and disadvantages of the current methodologies. In the final chapter Du ., provide an extensive review on metabolic glycoengineering of sialic acids. Metabolic glycoengineering of living cells and animals is an increasingly powerful method whereby non-natural analogs of N-acetylmannosamine are integrated into the sialic acid pathway. This then permits the dynamic characterization of metabolically incorporated non-natural sialic acid into cell surface sialoglycoconjugates in place of the natural sugar. This makes metabolic glycoengineering one of the most innovative tools available for the study of sialic acid dynamics.

Semester Paper | Biochemistry for Medics – Lecture Notes

Ganglioside Biosynthesis Pathway to GM2 When cursor points to a box further details will be displayed in a tooltip window

Cerebellar granule cells, differentiated in vitro, were parallelly fed with [Sph-3H]GM1 and [stearoyl-14C]GM1, under identical conditions (10-6 M ganglioside; pulse, from 1-4 h; chase, up to 24 h after 4 h pulse) and the salvage pathways of sphingosine and stearic acid were investigated. It was observed that both sphingosine and stearic acid, liberated during the intralysosomal degradation of ganglioside, are metabolically recycled, along distinct pathways. Sphingosine is used for the biosynthesis of a number of sphingolipids, particularly ceramide, glucosyl-ceramide, gangliosides and sphingomyelin; stearic acid is utilized for the biosynthesis of sphingolipids, and to a greater extent, glycero-phospholipids, especially those endogenously richer in stearic acid (phosphatidyl-ethanolamine and phosphatidyl-choline). No evidence was provided for a salvage pathway for ceramide.

AB - Roles for UDP-GlcNAc 2-epimerase/ManNAc 6-kinase (GNE) beyond controlling flux into the sialic acid biosynthetic pathway by converting UDP-GlcNAc to N-acetylmannosamine are described in this report. Overexpression of recombinant GNE in human embryonic kidney (HEK AD293) cells led to an increase in mRNA levels for ST3Gal5 (GM3 synthase) and ST8Sia1 (GD3 synthase) as well as the biosynthetic products of these sialyltransferases, the GM3 and GD3 gangliosides. Conversely, down-regulation of GNE by RNA interference methods had the opposite, but consistent, effect of lowering ST3Gal5 and ST8Sia1 mRNAs and reducing GM3 and GD3 levels. Control experiments ensured that GNE-mediated changes in sialyltransferase expression and ganglioside biosynthesis were not the result of altered flux through the sialic acid pathway. Interestingly, exogenous GM3 and GD3 also changed the expression of GNE and led to reduced ST3Gal5 and ST8Sia1 mRNA levels, demonstrating a reciprocating feedback mechanism where gangliosides regulate upstream biosynthetic enzymes. Cellular responses to the GNE-mediated changes in ST3Gal5 and ST8Sia1 expression and GM3 and GD3 levels were investigated next. Conditions that led to reduced ganglioside production (e.g. short hairpin RNA exposure) stimulated proliferation, whereas conditions that resulted in increased ganglioside levels (e.g. recombinant GNE and exogenous gangliosides) led to reduced proliferation with a concomitant increase in apoptosis. Finally, changes to BiP expression and ERK1/2 phosphorylation consistent with apoptosis and proliferation, respectively, were observed. These results provide examples of specific biochemical pathways, other than sialic acid metabolism, that are influenced by GNE.

Glycosylation Pathways in the Biosynthesis of Gangliosides in Melanoma and Neuroblastoma Cells: Relative Glycosyltransferase Levels ..
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Biosynthesis of the major brain gangliosides GD1a and …

N2 - Cerebellar granule cells, differentiated in vitro, were parallelly fed with [Sph-3H]GM1 and [stearoyl-14C]GM1, under identical conditions (10-6 M ganglioside; pulse, from 1-4 h; chase, up to 24 h after 4 h pulse) and the salvage pathways of sphingosine and stearic acid were investigated. It was observed that both sphingosine and stearic acid, liberated during the intralysosomal degradation of ganglioside, are metabolically recycled, along distinct pathways. Sphingosine is used for the biosynthesis of a number of sphingolipids, particularly ceramide, glucosyl-ceramide, gangliosides and sphingomyelin; stearic acid is utilized for the biosynthesis of sphingolipids, and to a greater extent, glycero-phospholipids, especially those endogenously richer in stearic acid (phosphatidyl-ethanolamine and phosphatidyl-choline). No evidence was provided for a salvage pathway for ceramide.

Biosynthesis of the major brain ..

AB - Cerebellar granule cells, differentiated in vitro, were parallelly fed with [Sph-3H]GM1 and [stearoyl-14C]GM1, under identical conditions (10-6 M ganglioside; pulse, from 1-4 h; chase, up to 24 h after 4 h pulse) and the salvage pathways of sphingosine and stearic acid were investigated. It was observed that both sphingosine and stearic acid, liberated during the intralysosomal degradation of ganglioside, are metabolically recycled, along distinct pathways. Sphingosine is used for the biosynthesis of a number of sphingolipids, particularly ceramide, glucosyl-ceramide, gangliosides and sphingomyelin; stearic acid is utilized for the biosynthesis of sphingolipids, and to a greater extent, glycero-phospholipids, especially those endogenously richer in stearic acid (phosphatidyl-ethanolamine and phosphatidyl-choline). No evidence was provided for a salvage pathway for ceramide.

GANGLIOSIDE BIOSYNTHESIS MODULATORS

The growing awareness about the significance of sialic acids in human health and disease has led to an increase in research into sialic acid chemistry, biochemistry and cell biology. A eBook devoted to the description of sialic acid structure and biosynthesis, as well as the function of sialic acid in healthy cell function and disease is long overdue. In fact since the last comprehesive book published in the field in 1995 (“Biology of the Sialic Acids” by Abraham Rosenberg) the field of Sialobiology has exponentially grown. For example, many of the key enzymes involved in sialic acid biosynthesis, as well as the vast majority of sialic acid binding lectins involved in immune recognition, have only been cloned, characterised and structurally eluciated since the publication of “Biology of the Sialic Acids”. Therefore, this eBook is very timely and will prove to be an excellent reference work for a wide range of biomedical research scientists.

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