Glycolipids of marine invertebrates

Molecular cloning of cytidine monophospho-N-acetylneuraminic acid hydroxylase. Regulation of species- and tissue-specific expression of N-glycolylneuraminic acid

Cytidine monophospho-N-acetylneuraminic acid (CMP-NeuAc) hydroxylase, which is the key enzyme for the synthesis of N-glycolylneuraminic acid (NeuGc), has been purified from the cytosolic fraction of mouse liver, as described in our previous paper. The amino acid sequences of the purified CMP-NeuAc hydroxylase, and peptides obtained by lysylendopeptidase digestion, were used to synthesize specific oligonucleotide primers. A mouse cDNA clone of the enzyme was obtained by a combination of the polymerase chain reaction and rapid amplification of cDNA ends. The sequence of the clone contained an open reading frame coding for a protein of 577 amino acids with a predicted molecular mass of 66 kDa. The deduced sequence included the amino acid sequences obtained for the purified enzyme and peptides, and a complete match was obtained for 159 residues. The enzyme has neither a signal peptide sequence nor a membrane spanning domain, which is consistent with localization of the enzyme in the cytosol. Transfection of a cDNA construct to COS-1 cells increased the enzyme activity and the amount of NeuGc. Comparison of the sequence with GenBank data indicated that no similar sequence has been reported so far. Northern blot analysis of various mouse tissues with the enzyme cDNA as a probe indicated that expression of NeuGc is related to the level of CMP-NeuAc hydroxylase mRNA. On Southern blot analysis with the same probe, cross-hybridizing bands were detected in the human and fish genomes.

An inducible arylsulfatase of Volvox carteri with properties suitable for a reporter-gene system. Purification, characterization and molecular cloning

The multicellular green flagellate Volvox carteri synthesizes a periplasmic arylsulfatase in response to sulfur deprivation. The inducible enzyme has been purified to homogeneity and characterized. The corresponding gene and cDNA have been cloned. Determination of the sequence of genomic clones and comparisons to the cDNA sequence, revealed sixteen introns and seventeen exons that encode a 649-amino-acid polypeptide chain. Since the arylsulfatase enzyme is readily assayed using chromogenic substrates, but is not detectable in cells grown in sulfate-containing medium, the gene encoding arylsulfatase may be useful as a reporter gene in V. carteri. In addition, the highly regulated promoter of the arylsulfatase gene suggests its suitability as a tool for producing inducible expression vectors for cloned genes.

Gulose as a constituent of a glycoprotein

The aldohexose gulose was identified as a constituent of a hydroxyproline-rich glycopeptide derived from the glycoprotein SSG 185. This glycoprotein is part of the extracellular matrix of the green alga Volvox carteri. The gulose residue occupies a terminal position in the corresponding saccharide.

Occurrence of ceramide digalactoside as the main glycosphingolipid in the marine sponge Halichondria japonica

The main glycosphingolipid of the sponge Halichondria japonica was isolated and its structure was determined to be ceramide digalactoside, Gal alpha 1----4Gal beta 1----1Cer, using FAB/MS, IR, 1H-NMR and chemical methods such as permethylation analysis and degradation techniques. The ceramide moiety was composed mainly of 4-hydroxy-iso-octadecasphinganine and 2-hydroxy-docosanoic acid. Interestingly, the branched long-chain bases were comprised of 70% total long-chain bases and 17.5% 4-hydroxy-anteiso-nonadecasphinganine. Ceramide monohexoside, consisting of galactosyl ceramide (81%) and glucosyl ceramide (19%), was also isolated as a minor component. The composition of the ceramide moiety was nearly the same as that of ceramide digalactoside.

The extracellular matrix of Volvox carteri: molecular structure of the cellular compartment

The extracellular matrix (ECM) of Volvox contains insoluble fibrous layers that surround individual cells at a distance to form contiguous cellular compartments. Using immunological techniques, we identified a sulfated surface glycoprotein (SSG 185) as the monomeric precursor of this substructure within the ECM. The primary structure of the SSG 185 poly-peptide chain has been derived from cDNA and genomic DNA. A central domain of the protein, 80 amino acid residues long, consists almost exclusively of hydroxyproline residues. The chemical structure of the highly sulfated polysaccharide covalently attached to SSG 185 has been determined by permethylation analysis. As revealed by EM, SSG 185 is a rod-shaped molecule with a 21-nm-long polysaccharide strand protruding from its central region. The chemical nature of the cross-links between SSG 185 monomers is discussed.

A phosphodiester bridge between two arabinose residues as a structural element of an extracellular glycoprotein of Volvox carteri

The sulphated glycoprotein SSG 185 is the monomeric precursor of a highly aggregated structural element in the extracellular matrix of the multicellular green alga Volvox carteri. A phosphodiester of arabinose was isolated from a saccharide fragment of SSG 185. The structure of this phosphodiester was investigated by methylation analysis, 13C-NMR, photometric methods and enzymatic assays and identified as D-Araiota-5-phospho-5-D-Araiota. The function of this phosphodiester bridge as a crosslink of different carbohydrate chains in SSG 185 is discussed.

Gangliosides of the starfish Aphelasterias japonica, evidence for a new linkage between two N-glycolylneuraminic acid residues through the hydroxy group of the glycolic acid residue

Mono- and disialogangliosides containing glucose, galactose and sialic acids were isolated from the total lipid extract of hepatopancreas of the starfish Aphelasterias japonica. Their structures were elucidated by total and partial acid hydrolysis, trideuteriomethylation analysis, neuraminidase treatment, chromium trioxide oxidation, methanolysis and periodate oxidation. The monosialoganglioside was identified as 8-O-methyl-N-glycolylneuraminosyl-alpha-(2-3)-galactosyl-beta-(1- 4)-glucosyl-beta-(1-1)-ceramide. The disialoganglioside has the additional N-glycolylneuraminic acid or its 8-O-methyl derivative residue at the subterminal position to which the terminal sialic acid residue is linked through the hydroxy group of the glycolic acid unit. The long-chain bases were found to be mixtures of phytosphingosines with both branched and linear chains, and the fatty acids were shown to be mixtures of normal and alpha-hydroxy fatty acids, the latter amounted to about 90% of the fatty-acid mixtures. The composition of the lipid moieties of the gangliosides was determined by GLC and GLC-MS.

Phylogeny and ontogeny of vertebrate brain gangliosides

Gangliosides evolved relatively recently in the history of life, thus their contribution to fundamental cellular processes must be ancillary to or superimposed on preexisting mechanisms. Brain ganglioside patterns vary along taxonomic lines in a fairly conservative fashion, indicating that general ecophysiological factors have probably provided the major selective constraints. During brain development in birds and mammals, gangliosides pass through a transient stage of pattern complexity that may reflect their reptilian ancestry. While this ganglioside heterogeneity could provide positional information within the developing tissue, it might merely reflect a necessary but incidental transition to the handful of major gangliosides essential to mature brain function.

A novel sialoglycolipid from hepatopancreas of the starfish Patiria pectinifera

An unusual sialoglycolipid containing D-glucose, D-galactose, L-arabinose and N-acetylneuraminic acid was purified from the total lipid extract of hepatopancreas of the starfish Patiria pectinifera. The structure of the sialolipid was studied by total and partial acid hydrolysis, methanolysis, periodate oxidation, methylation, chromium trioxide oxidation and enzymatic hydrolysis. The oligosaccharide chain of the sialolipid is branched: N-acetylneuraminic acid is located in the inner part of the carbohydrate chain; the arabinose residues are in furanose forms and are located at the non-reducing ends of the carbohydrate chain. The long-chain bases are C16-, C17- and C18-phytospingosines with both branched and normal chains. Only alpha-hydroxy fatty acids are found, C22-, C23- and C24-alpha-hydroxy fatty acids represent approx. 95% of the total fatty acids.

Membrane glycolipids: regional synthesis and axonal transport in a single identified neuron of Aplysia californica

Glycolipids moving along an identified axon Aplysia californica were synthesized and incorporated into intracytoplasmic membranes solely in the perikaryon: direct injection of tritiated sugar into the axon revealed no local synthesis or exchange. There was no indication for transfer into axoplasm from glia. Insertion of glycolipids into nascent membranes occurs coordinately with insertion of protein components in the cell body.

Ganglioside structures and distribution: are they localized at the nerve ending?

Gangliosides generally provide a small portion of the complex carbohydrate content of cell surfaces. An exception is the central nervous system where they comprise up to 5--10% of the total lipid of some membranes. This tissue is unique in that the quantity of lipid-bound sialic acid exceeds that of the protein-bound fraction. Over 30 different molecular species have been characterized to date. These range in complexity from sialosylgalactosyl ceramide with 2 sugars to the pentasialoganglioside of fish brain with 9 carbohydrate units. Virtually all cellular and subcellular fractions of brain that have been carefully examined contain gangliosides to one degree or another, but the majority of brain ganglioside is located in the neurons. Their mode of distribution within the neuron has not been entirely clarified by subcellular studies. Calculations based on reported values for axon terminal density and synaptosomal ganglioside concentration in the rat reveal that nerve endings contribute less than 12% of total cerebral cortical ganglioside. It is concluded that the plasma membranes of neuronal processes contain most of the neuronal ganglioside. These and other considerations suggest the possibility that gangliosides may be distributed over the entire neuronal surface.

Isolation and structural studies of a sulfated sialosphingolipid from the sea urchin Echinocardium cordatum

Three sialosphingolipids have been isolated from a lipid extract of gonads of the sea urchin Echinocardium cordatum by partition dialysis and DEAE-cellulose column chromatography. The structure of the sialosphingolipid containing sulfate group has been established. On the basis of the results of total and partial acid hydrolysis, methanolysis, methylation, periodate oxidation and enzymatic hydrolysis with neuraminidase the sulfated sialosphingolipid was identified as 8-sulfate-sialyl-alpha-(2 leads to 6)glucopyranosyl-(1 leads to 1)ceramide. The long-chain bases were mainly phytosphingosine and its C16 homologue. The fatty acids of the sialosphingolipid were the mixture of normal and alpha-hydroxy fatty acids, their compositions were analysed by gas-liquid chromatography.

A genetic model for the evolution of the glycosphingolipids

The glycosphingolipids have been found in many animal tissues, but the complexity of their molecular structure varies considerably among the different phyla. Relatively simple structures have been found in invertebrate species, while the most complex have been demonstrated in brain tissue of modern fishes and amphibians. The data on the phylogenetic distribution of the glycosphingolipids has been interpreted to indicate that a significant number of gene duplications, involving many different structural genes, may have occurred during a few specific periods of vertebrate evolution. The transition from invertebrate to jawless vertebrate, the divergence of rays and skates from true sharks, the advent of modern bony fishes and the transition from aquatic to terrestrial vertebrates, each could have veen accompained by duplications of genes involved in the synthesis and degradation of glycosphingolipids. The evolutionary study of such a multi-enzyme system may be one means to detect alterations in the genome as a whole. The apparent correspondence in time of these gene duplications involved in glycosphingolipid metabolism and periods of rapid vertebrate evolution which may have been accompanied by significant increases in the amount of cellular DNA suggests that such changes may have occurred via the mechanism of tetraploidization.