No description available.

A choleplasma axanthum is one of the few procaryotes, and the only member of the Mollicutes, known to contain phosphosphingolipids. Examination of strain S743 for glycolipids revealed the presence of glucosides of cholesterol and galactosides of glycerol as the predominant glycolipids. The major component is acylated diglucosylcholesterol, followed by monogalactosyldiacylglycerol and monoglucosylcholesterol. The glucose residues of the sterol-based compounds appear to be α-linked pyranoses, while the galactose of the glycerol-based lipid is an α-linked furanose. The 'glycolipid' fraction also contained N-(3-hydroxy)acyl sphinganines with varying degrees of O-acylation. None of these ceramide derivatives was linked to carbohydrate. The major glycolipid, tentatively identified as ga-d-glucopyranosyl-(1 → 3)-(O-acyl)α-d-glucopyranosyl-(1 → 3)- along with its deacylated derivative, appears to be the first reported instance of steryl diglycosides among procaryotes, in contrast to the steryl monoglycosides, which are common to other mycoplasmata and some spirochetes.

No description available.

No description available.

The cell membrane is a complex structure with many functions that can affect cellular processes. For this reason, a model possessing characteristics similar to those of the natural cell membrane is required for the investigation of various functions and properties belonging to this important structure. Presented is the synthesis of a glycolipid analogue possessing both a C-4’ thiol functionalization (for binding to an Au(111) electrode) and an anomeric triazole-linked phytanyl chain (for integration into a phospholipid bilayer). Additionally, a similar analogue without thiol functionalization was synthesized for use as a dilution molecule to prevent aggregation of the tether analogue during monolayer assembly. Aqueous compartments will exist above and below the bilayer allowing for future integration and functional analysis of membrane proteins. Glycosylation at the anomeric position of a lactosyl donor with propargyl alcohol gave a propargyl lactoside that underwent several steps of selective protection to give access at O-4’ for triflation. Displacement of the triflate gave a thioacetate functionalized disaccharide. Both the propargyl lactoside and the thioacetate functionalized disaccharide underwent copper-catalyzed azide-alkyne cycloadditions with phytanyl azide. Subsequent deprotections gave two novel glycolipid analogues. / NSERC

Natural killer T (NKT) cells are a subset of T cells that modify a variety of immune responses. NKT cells recognize glycolipid antigen presented by a molecule called CD1d, a nonclassical antigen-presenting molecule. The best known subset of CD1d-dependent NKT cells expresses an invariant T cell receptor Vα (TCR-α) chain. These are referred to as type I or invariant NKT (iNKT) cells. When stimulated by a glycolipid, NKT cells rapidly release large amounts of cytokines. Cytokines released by NKT cells can induce either Th1 or Th2 responses. Th1 cytokines are effective in regulating bacterial, parasitic, and viral infections. But Th1 responses are also involved in some autoimmune diseases, such as type 1 diabetes, lupus, rheumatoid arthritis, and allergen-induced asthma. Th2 cytokines can attenuate proinflammatory Th1 responses and therefore prevent some autoimmune diseases. Lysosomal processing and CD1d loading is very important in regulating the stimulatory properties of antigens. Analogs of KRN7000, with small molecules appended on C6” position of the galactose portion, do not significantly change stimulation of NKT cells. The question is if the substitution at this position would influence the lysosomal processing. Two sets of mono- and disaccharides with and without substitution at C6” position were prepared and evaluated the NKT cell stimulatory properties. The substitution at the C6” position of the sugar moiety of glycolipids do not significantly impact the stimulatory properties of glycolipids and their processing in lysosome. Small changes at C6” are well tolerated. A double bond in the acyl chain and modification of the C6” functional group helped the glycolipid loading into CD1d and NKT cells stimulation. PBS57 is 100 times more active than KRN 7000 in stimulation of NKT cells responses in vitro and in vivo. This improvement is probably due to increasing solubility and improving binding ability with the CD1d.

No / A series of lipoamino acid-based glycolipids were synthesised. Suitably derivatised lipoamino acid derivatives were prepared and conjugated to monosaccharides (including glycosyl azides, isothiocyanates, thiols and sulphones) to yield novel O-, N-, S- and C-linked glycolipids in good yields. Their potential to improve the oral absorption of piperacillin is reported.

<p>The synthesis and breakdown of sugars is one of the most important functions in Nature. Consequently, sugar structures are used both as energy storage and as building blocks to stabilise and protect the cell. The formation of these structures is performed by glycosyltransferases (GT), an enzyme group structurally conserved within all kingdoms. Until now, only two different folds have been discovered by crystallisation of GTs, i.e. GT-A and GT-B. A third fold family has however been proposed by fold predictions. In this thesis, a multivariate data analysis was successfully used in classifying and predicting both fold and reaction mechanism (inverting or retaining) of GTs. This method was also used to obtain information about the separating parameters for the reaction mechanism classification. This information could be traced back to the amino acid sequence. The method could as well be used to analyse and identify the properties of membrane binding regions of GTs, and subsequently distinguish soluble from membrane-associated enzymes. Most functionally characterised enzymes only use one substrate, synthesising one product. <i>Mycoplasma pneumoniae</i>, a common human pathogen with a small genome has only three proposed GTs. The bacterium was, however expected to have a greater number of GTs, due to its ability to make both glycolipids and capsule. Here we have determined the function of one of these enzymes, MPN483 and discovered its ability to both use different acceptors, and make elongated glycolipids with up to three galactose residues, with both DAG and ceramide as the base. Many of the synthesised glycolipids were also found to be immunogenic, hence showing their biological importance. The properties of lipids are known to be important for the function of a biological membrane. We have here shown that not only the charge but also the shape of the lipids are important for several protein mediated membrane processes in <i>Echerichia coli</i>, such as the function of the LacY.</p>

The synthesis and breakdown of sugars is one of the most important functions in Nature. Consequently, sugar structures are used both as energy storage and as building blocks to stabilise and protect the cell. The formation of these structures is performed by glycosyltransferases (GT), an enzyme group structurally conserved within all kingdoms. Until now, only two different folds have been discovered by crystallisation of GTs, i.e. GT-A and GT-B. A third fold family has however been proposed by fold predictions. In this thesis, a multivariate data analysis was successfully used in classifying and predicting both fold and reaction mechanism (inverting or retaining) of GTs. This method was also used to obtain information about the separating parameters for the reaction mechanism classification. This information could be traced back to the amino acid sequence. The method could as well be used to analyse and identify the properties of membrane binding regions of GTs, and subsequently distinguish soluble from membrane-associated enzymes. Most functionally characterised enzymes only use one substrate, synthesising one product. Mycoplasma pneumoniae, a common human pathogen with a small genome has only three proposed GTs. The bacterium was, however expected to have a greater number of GTs, due to its ability to make both glycolipids and capsule. Here we have determined the function of one of these enzymes, MPN483 and discovered its ability to both use different acceptors, and make elongated glycolipids with up to three galactose residues, with both DAG and ceramide as the base. Many of the synthesised glycolipids were also found to be immunogenic, hence showing their biological importance. The properties of lipids are known to be important for the function of a biological membrane. We have here shown that not only the charge but also the shape of the lipids are important for several protein mediated membrane processes in Echerichia coli, such as the function of the LacY.

The sciatic nerves of rats were crushed with fine forceps and allowed to survive for 3 or 7 days, at which time the 5th lumbar dorsal root ganglion was injected with [3H]glucosamine. Animals were killed 18 h later and the nerves proximal and distal to the crush site were cut into 3 mm segments. Gangliosides were purified from these segments, and radioactivity was separately measured in gangliosides, neutral glycolipids and glycoprotein. For all 3 fractions, radioactivity was distributed similarly between the crush site the point of maximum axonal elongation. A second smaller peak of ganglioside radioactivity was seen to span a few segments immeidately distal to the point of maximum axonal elongation. We propose two possible explanation for this: (1) it represents ganglioside synthesis by Schwann cells (from blood-borne [3H]glucosamine) as part of the mitogenic response of these cells to the reappearance of axons; or (2) recently synthesized, transported gangliosides are released from the growth cone and taken up by adjacent mitogenic Schwann cells.