Rotor synchronization of radiofrequency and gradient pulses in high-resolution magic angle spinning NMR

We have investigated the extent to which rotor synchronization of radiofrequency pulses leads to spectral improvement in high-resolution magic angle spinning NMR experiments. Several pulse sequences were tested, and the effect was found to be maximal in homonuclear TOCSY spectra. The physicochemical nature of the sample plays a role in the phenomenon, as rotor synchronization allows the refocusing of residual anisotropic interactions. However, even in a liquid sample the effects were visible. Radial inhomogeneities of the radiofrequency field were identified as an important source of the problem.

1H NMR study on the binding of Pin1 Trp-Trp domain with phosphothreonine peptides

The recent crystal structure of Pin1 protein bound to a doubly phosphorylated peptide from the C-terminal domain of RNA polymerase II revealed that binding interactions between Pin1 and its substrate take place through its Trp-Trp (WW) domain at the level of the loop Ser(11)-Arg(12) and the aromatic pair Tyr(18)-Trp(29), and showed a trans conformation for both pSer-Pro peptide bonds. However, the orientation of the ligand in the aromatic recognition groove still could be sequence-specific, as previously observed in SH3 domains complexed by peptide ligands or for different class of WW domains (Zarrinpar, A., and Lim, W. A. (2000) Nat. Struct. Biol. 7, 611-613). Because the bound peptide conformation could also differ as observed for peptide ligands bound to the 14-3-3 domain, ligand orientation and conformation for two other biologically relevant monophosphate substrates, one derived from the Cdc25 phosphatase of Xenopus laevis (EQPLpTPVTDL) and another from the human tau protein (KVSVVRpTPPKSPS) in complex with the WW domain are here studied by solution NMR methods. First, the proton resonance perturbations on the WW domain upon complexation with both peptide ligands were determined to be essentially located in the positively charged beta-hairpin Ser(11)-Gly(15) and around the aromatic Trp(29). Dissociation equilibrium constants of 117 and 230 microm for Cdc25 and tau peptides, respectively, were found. Several intermolecular nuclear Overhauser effects between WW domain and substrates were obtained from a ligand-saturated solution and were used to determine the structures of the complexes in solution. We found a similar N to C orientation as the one observed in the crystal complex structure of Pin1 and a trans conformation for the pThr-Pro peptidic bond in both peptide ligands, thereby indicating a unique binding scheme for the Pin1 WW domain to its multiple substrates.

In vivo detection of the cyclic osmoregulated periplasmic glucan of Ralstonia solanacearum by high-resolution magic angle spinning NMR

We investigate the mobility of the osmoregulated periplasmic glucans of Ralstonia solanacearum in the bacterial periplasm through the use of high-resolution (HR) NMR spectroscopy under static and magic angle spinning (MAS) conditions. Because the nature of periplasm is far from an isotropic aqueous solution, the molecules could be freely diffusing or rather associated to a periplasmic protein, a membrane protein, a lipid, or the peptidoglycan. HR MAS NMR spectroscopy leads to more reproducible results and allows the in vivo detection and characterization of the complex molecule.

High resolution magic angle spinning NMR in combinatorial chemistry

Solid phase organic chemistry coupled with combinatorial methods promises to increase dramatically the diversity and number of small molecules available for medical and biological applications. However, optimizing the reaction conditions can be a time consuming step, especially since analytical tools to monitor reaction progress and detect impurities for solid phase chemistry are less developed than for solution chemistry. The use of high resolution magic angle spinning (HRMAS) NMR is described here as such an analytical tool. Whereas initial applications of molecular identification using deuterated organic solvents to swell the resins presented a significant gain in time over the cleave-and-analysis methods, the introduction of a differential diffusion filter has made immediate recording of spectra possible without any sample treatment. The applications of HRMAS NMR to different solid supports that are used in combinatorial chemistry will be described in terms of rapidity, robustness and sensitivity.

p13(SUC1) and the WW domain of PIN1 bind to the same phosphothreonine-proline epitope

The WW domain of the human PIN1 and p13(SUC1), a subunit of the cyclin-dependent kinase complex, were previously shown to be involved in the regulation of the cyclin-dependent kinase complex activity at the entry into mitosis, by an unresolved molecular mechanism. We report here experimental evidence for the direct interaction of p13(SUC1) with a model CDC25 peptide, dependent on the phosphorylation state of its threonine. Chemical shift perturbation of backbone (1)H(N), (15)N, and (13)Calpha resonances during NMR titration experiments allows accurate identification of the binding site, primarily localized around the anion-binding site, occupied in the crystal structure of the homologous p9(CKSHs2) by a sulfate molecule. The epitope recognized by p13(SUC1) includes the proline at position +1 of the phosphothreonine, as was shown by the decrease in affinity for a mutated CDC25 phosphopeptide, containing an alanine/proline substitution. No direct interaction between the PIN1 WW domain or its catalytic proline cis/trans-isomerase domain and p13(SUC1) was detected, but our study showed that in vitro the WW domain of the human PIN1 antagonizes the binding of the p13(SUC1) to the CDC25 phosphopeptide, by binding to the same phosphoepitope. We thus propose that the full cyclin-dependent kinase complex stimulates the phosphorylation of CDC25 through binding of its p13(SUC1) module to the phosphoepitope of the substrate and that the reported WW antagonism of p13(SUC1)-stimulated CDC25 phosphorylation is caused by competitive binding of both protein modules to the same phosphoepitope.

Capsular polysaccharide produced by the thermophilic cyanobacterium Mastigocladus laminosus. Structural study of an undecasaccharide obtained by lithium degradation

The capsular polysaccharide produced by the thermophilic cyanobacterium Mastigocladus laminosus has been subjected to a specific degradation with lithium in ethylenediamine. The released undecasaccharide attached to one unit of tetrahydroxycyclopentanecarboxylic acid has been characterized by a combination of 2D nuclear magnetic resonance spectroscopy, mass spectrometry, monosaccharidic composition and linkage analyses. From the overlap of the structure of this oligosaccharide with previously identified di-, tri- and pentasaccharides released by mild acid hydrolysis, the capsular polysaccharide was deduced to have a pentadecasaccharide repeating unit with the following structure:

Characterization of a multi-lipopeptides mixture used as an HIV-1 vaccine candidate

A multi-component vaccine has been defined, which contains six different synthetic 24- to 32-amino acid lipopeptides derived from the sequence of HIV-1 proteins. The physicochemical properties of the lipopeptide components were compatible with multi-dimensional analysis, using RP-HPLC, Edman sequencing, electrospray mass spectrometry, and 2D-NMR. Detailed analysis of the impurity profiles led to the detection and evaluation of the relative proportions of most by-products: several contaminants resulted from the formation of acetylated fragments, transpeptidation reactions with succinimide or piperidide formation, or methionine and/or tryptophan mono-oxidations. The first batch to be produced underwent extensive pharmacotoxicological testings to confirm its safety; this vaccine candidate has now been used in phase I clinical trials. Despite the complexity of such multi-lipopeptide vaccines, our findings suggest the possibility of preparing a clear and precise assignment of by-products to toxicologically qualified impurities in the eventuality of a future production of several successive batches.

Glycerol's influence on the oxidized insulin B-chain conformation in relation to the selectivity variation of subtilisin: an nuclear magnetic resonance and simulated annealing study

Glycerol, employed to mimic biological media with restricted water activity, has been shown to modify the activity of subtilisin BPN', an endopeptidase, towards the oxidized insulin B-chain, a well-studied substrate (FEBS Lett., 279 (1991) 123-131). Without minimizing the role of the microenvironment on the enzyme, we have studied the effect of glycerol addition on the structure of the enzyme substrate by homonuclear NMR spectroscopy and simulated annealing. Our results show that, in water, the oxidized insulin B-chain tertiary structure loses its central helix (residues B9-B19) and presents a folded structure with a flexible turn (residues B18-B24) in the beta-turn region of the insulin B-chain; whereas, in glycerol, the peptide is more rigid and is not folded. Moreover, in our experimental conditions, glycerol favors beta-strand secondary structure formation. Following these results, hypotheses about the differences observed in enzymatic activity on this substrate in glycerol have been postulated.

Identification of a sequence-dependent reversible acylation of tosylarginine in a peptidyl-resin reacted with isonicotinyl p-nitrophenylcarbonate

In this paper, we report on the identification of an unexpected acylation that occurred on the solid phase when a peptide containing an unprotected lysyl and a tosyl-protected arginyl residue was treated with a large excess of isonicotinyl p-nitrophenylcarbonate. NMR and matrix-assisted laser desorption/ionisation -post-source decay analysis of the purified peptide demonstrated the presence of one extra isonicotinyloxycarbonyl (iNoc) group located on the omega nitrogen atom of the arginine which was adjacent to the Lys(iNoc). The desired peptide was obtained by quantitative removal of the unwanted iNoc group during a brief treatment with diluted aqueous hydrazine.

Sulfated lewis X determinants as a major structural motif in glycans from LS174T-HM7 human colon carcinoma mucin

This article describes oligosaccharide structures of mucin isolated from nude mouse xenograft tumors produced by LS174T-HM7 cells, a subline of the human colon carcinoma LS174T with higher metastatic tendency and higher mucin production. A striking feature of the oligosaccharides of the LS174T-HM7 xenograft tumor mucin was a predominance of sulfated Lewis X determinants: HSO3-Galbeta1-4(Fucalpha1-3)GlcNAc. In addition to one previously known saccharide with one sulfated Lewis X determinant, the HM7 xenograft tumor mucin contained multiple novel structures containing one, two, or three sulfated Lewis X determinants. This determinant, known to act as a selectin ligand, has been found previously in minor saccharide components of human milk as well as mucins, but never before as a predominant structure in one mucin source.

Structural characterization of the exocellular polysaccharides produced by Streptococcus thermophilus SFi39 and SFi12

We investigated the structures of the exopolysaccharides (EPSs) produced by Streptococcus thermophilus SFi39 and SFi12. Both polymers were found to have molecular masses of greater than 2 x 10(6) Da. The SFi39 EPS consisted of D-glucose and D-galactose in a molar ratio of 1:1, whereas the SFi12 EPS was composed of D-galactose, L-rhamnose, and D-glucose in a molar ratio of 3:2:1. Methylation analysis of and nuclear magnetic resonance spectra recorded from the native polysaccharide, as well as oligosaccharides released by partial acid hydrolysis, allowed the complete structural determination of the SFi39 EPS, which consists of the following tetrasaccharide repeating unit: [formula: see text] Similar spectra recorded only from the native polysaccharide were sufficient to allow the structural determination of the SFi12 EPS, which consists of the following hexasaccharide repeating unit: [formula: see text] This study shows that the texturizing properties of different S. thermophilus ropy strains are based on the production of EPSs exhibiting chemical similarities but structural differences.

Diagnosis of a case of acute chloroquine poisoning using 1H NMR spectroscopy: characterisation of drug metabolites in urine

Analysis of biological fluids by proton nuclear magnetic resonance spectroscopy (1H NMR) is a promising tool in clinical biology. We have used this method for a rapid toxicological screening in the case of a suicide attempt. A urine sample was analysed at 300 and 600 MHz by 1D and 2D sequences (J-resolved and TOCSY) in a short experimental time. Quantification was realized by peak integration of the 1D spectrum. The results showed the presence of chloroquine and its major metabolite monodesethylchloroquine at concentrations of 462 and 140 mg/L, respectively. Ethanol was also detected in the spectrum. It can be concluded that 1H NMR provides many advantages as a tool for clinical diagnosis in a case of acute intoxication.

Characterization of a new family of toxin-like peptides from the venom of the scorpion Leiurus quinquestriatus hebraeus. 1H-NMR structure of leiuropeptide II

To extend our knowledge about the structural features of short scorpion toxins, the ion-exchange fractions obtained from Leiurus quinquestriatus hebraeus venom were investigated by plasma desorption mass spectrometry in order to select low molecular mass polypeptides. Three toxin-like peptides with molecular mass close to 3 kDa, named leiuropeptides I, II and III, were purified and found devoid of any significant toxicity against mammals and insects. Their amino acid sequences revealed a cysteine pattern analogous to that of short-chain scorpion toxins. The solution structure of leiuropeptide II was determined by 2D 1H-NMR spectroscopy and indicated the presence of a helix accommodating a proline, connected to a two-standard beta-sheet by three disulfide bonds. The overall fold of leiuropeptide II is found to be similar to that of leiurotoxin I, a 31-residue toxin present in the same scorpion venom which acts on K+ channels. In order to rationalize the absence of toxicity, the electrostatic potential of leiuropeptide II was compared to that of leiurotoxin I. The peptide is characterized by a large negative zone around Glu4, Asp5 and Asp8 residues, beginning in the neighbourhood of the beta-turn and extending along the helix. In the same area, leiurotoxin I exhibits a positive surface, around Arg6 and Arg13 basic residues, which are essential for its receptor affinity.

Measurement of three-bond coupling constants in the osmoregulated periplasmic glucan of Burkholderia solanacearum

The cyclic osmoregulated periplasmic glucan produced by Burkholderia solanacearum contains 13 glucose units, all beta-(1-2) linked except for one alpha-(1-6) linkage. We report here the measurement of the 3J(C1-H2') and 3J(H1-C2') coupling constants, characterizing the glycosidic linkages, through the use of a 13C/12C double half-filtered NOESY experiments. The values obtained give information about the (phi, psi) angles of the different linkages. The results presented from an important step towards a detailed experimental model of the cyclic glucan, which might allow us to clarify its biological role and establish whether the cavity of these molecules is compatible with the capability of complexing host molecular signals.

A water-soluble beta-D-glucan from Boletus erythropus

The main component of a water extract of Boletus erythropus fruiting bodies is a M(r) 10(6) glucan. The use of classical structural analysis and HMQC (heteronuclear multiple quantum coherence) NMR experiments indicates a (1-->3) linked beta-D-glucan structure with a single glucose residue attached to O-6 of the main chain and a branching frequency of 1/3.

Structural determination of symbiotic nodulation factors from the broad host-range Rhizobium species NGR234

Nod factors are secreted lipo-oligosaccharides produced by symbiotic nitrogen-fixing Rhizobium bacteria that induce nodule formation on the roots of host leguminous plants. Two biologically active fractions (NodNGRA and NodNGRB) were isolated by reversed-phase HPLC from the culture supernatant of a Nod factor overproducing strain of Rhizobium sp. NGR234. NodNGRA and NodNGRB are heterogeneous mixtures of N-acylated 2-O-methylfucosylated chitomers, in which the fucosyl residue may be either 3-sulfated (NodNGRA), or 4-O-acetylated or nonsubstituted (NodNGRB). Structurally analogous series of compounds occur with either N-vaccenic (C18:1) or N-palmitic (C16:0) substituents. The presence of 6-O-carbamoyl groups on the GlcNMe-Acyl residue occurs on some molecules, while others are di-O-carbamoylated. Detailed structural analysis of seventeen Nod factors are reported here.

Cell-associated glucans of Burkholderia solanacearum and Xanthomonas campestris pv. citri: a new family of periplasmic glucans

The cell-associated glucans produced by Burkholderia solanacearum and Xanthomonas campestris pv. citri were isolated by trichloroacetic acid treatment and gel permeation chromatography. The compounds obtained were characterized by compositional analysis, matrix-assisted laser desorption ionization mass spectrometry, and high-performance anion-exchange chromatography. B. solanacearum synthesizes only a neutral cyclic glucan containing 13 glucose residues, and X. campestris pv. citri synthesizes a neutral cyclic glucan containing 16 glucose residues. The two glucans were further purified by high-performance anion-exchange chromatography. Methylation analysis revealed that these glucans are linked by 1,2-glycosidic bonds and one 1,6-glycosidic bond. Our 600-MHz homonuclear and 1H-13C heteronuclear nuclear magnetic resonance experiments revealed the presence of a single alpha-1,6-glycosidic linkage, whereas all other glucose residues are beta-1,2 linked. The presence of this single alpha-1,6 linkage, however, induces such structural constraints in these cyclic glucans that all individual glucose residues could be distinguished. The different anomeric proton signals allowed complete sequence-specific assignment of both glucans. The structural characteristics of these glucans contrast with those of the previously described osmoregulated periplasmic glucans.

Isolation and structures of glycoprotein-derived free oligosaccharides from the unfertilized eggs of Scyliorhinus caniculus. Characterization of the sequences galactose(alpha 1-4)galactose(beta 1-3)-N-acetylglucosamine and N-acetylneuraminic acid(alpha 2-6)galactose(beta 1-3)-N-acetylglucosamine

As previously reported [Ishii, K., Iwasaki, M., Inoue, S., Kenny, P. T. M., Komura, H. & Inoue, Y. (1989) J. Biol. Chem. 264, 1623-1630; Inoue, S., Iwasaki, M., Ishii, K., Kitajima, K. & Inoue, Y. (1989) J. Biol. Chem. 264, 18520-185261, the unfertilized eggs of two different species of fresh-water fish, Plecoglossus altivelis and Tribodolon hakonensis, contain relatively large amounts of free sialooligosaccharides. These oligosaccharides were found to derive from glycophosphoproteins, owing to the activity of a peptide - N4-(N-acetyl-beta-D-glucosaminyl)asparagine amidase [Iwasaki, M., Seko, A., Kitajima, K., Inoue, Y. & Inoue, S. (1992) J. Biol. Chem. 267, 24287-24296; Seko, A., Kitajima, K., Inoue, Y. & Inoue, S. (1991) J. Biol. Chem. 266, 22110-22114]. Here we describe a new type of free oligosaccharides, isolated from unfertilized eggs of Scyliorhinus caniculus. From the structural analysis, based upon 1H-NMR spectroscopy, the following glycan units are proposed.[Formula: see text]

Identification by NMR spectroscopy of oligosaccharides obtained by acidolysis of the capsular polysaccharides of a thermal biomass

This study deals with the chemical characterization of a capsular polysaccharide (CPS) produced by a thermal biomass largely comprising the cyanobacterium Mastigocladus laminosus. The sugar moiety of this polymer is composed of seven neutral monosaccharides (Rha, Fuc, Ara, Xyl, Man, Glc, Gal) and two uronic acids (GalA, GlcA). Proteins represent 18% of the dry weight of the CPS. Organic acid substituents (acetate, pyruvate, succinate) were also detected and estimated by high-performance liquid chromatography. The presence of sulfate groups (5% w/w) was observed, which represents a relatively rare feature for cyanobacteria. Acidic hydrolysis of the purified polysaccharide led to the isolation of four oligosaccharidic fractions. NMR spectroscopy studies of two of the four purified oligosaccharides allowed them to be identified as: alpha-GlcA-(1-->2)-alpha-GalA-(1-->2)-Man and alpha-GlcA-(1-->2)-alpha-GalA-(1-->2)-beta-Man-(1-->4)-beta-Gal-(1 -->2)-Rha.

Characterization of sheep hemopexin glycovariants

The hemopexin phenotype HpxB1 isolated from sheep serum, yields three major bands when subjected to starch gel and/or polyacrylamide gel electrophoresis which are here designated as subcomponents HpxB1-I, HpxB1-II and HpxB1-III. Electrospray mass spectrometric analysis of samples of the isolated subcomponents prepared by ion exchange chromatography showed that each was composed of three glycoproteins and that the major difference between the subcomponents was due to their constituent glycoproteins possessing different numbers of sialic acid residues. Combined analysis of the ESI-MS data and of the overall carbohydrate compositional data obtained by colorimetric procedures, leads to the composition of the glycan of each glycoprotein, and a combined methylation and 400 MHz H-NMR analysis of the alkaline cleaved glycans identified them as being of only the biantennary N-acetyllactosamine type. Taking into account the molecular mass, the carbohydrate content and structure it may be concluded that each of the constituent glycoproteins contain five N-glycosidically linked glycans.

Specificity of the isolectins from the plant cactus Machaerocereus eruca for oligosaccharides from porcine stomach mucin

Sugar specificity of the Machaerocereus eruca isolectins, MeAI and MeAII, has been determined by comparing the capacity of glycans with well defined structures to inhibit their haemagglutinating activity. Both are galactose-specific isolectins with high affinity for O-glycans. However, the two M. eruca isolectins recognize different oligosaccharidic sequences belonging to O-glycosidically linked glycans from porcine stomach mucin. The minimal structure recognized by MeAI on the porcine mucin glycans is the O-glycan core Gal beta 1,3GalNAc-ol, whereas MeAII has a more extended site and interacts with a biantennary O-glycan possessing the terminal trisaccharide Fuc alpha 1,2 (GalNAc alpha 1,3) Gal beta 1,4.

Structure of four acidic oligosaccharides from the jelly coat surrounding the eggs of Xenopus laevis

Novel acidic oligosaccharides were released by reductive beta-elimination from the jelly coat eggs of the Anuran Xenopus laevis. According to the structural analysis of these oligosaccharide-alditols, the following structures are proposed: [sequence: see text] where Kdn, 3-deoxy-D-glycero-D-galactononulosonic acid. These results confirm the species specificity of the glycanic structures present in the secretion of amphibian oviducts, and may form the basis of a specific egg-sperm recognition process.

Structure of six 3-deoxy-D-glycero-D-galacto-nonulosonic acid(Kdn)-containing oligosaccharide-alditols released from oviduct secretions of Ambystoma maculatum. Characterization of the sequence fucosyl(alpha 1-2)[fucosyl(alpha 1-3)]fucosyl(alpha 1-4)-3-deoxy-D-glycero-D-galacto-nonulosonic acid

The O-linked acidic oligosaccharides of the jelly coat surrounding the eggs of Ambystoma maculatum were analyzed by NMR spectroscopy. The structures of the major oligosaccharides were established as follows where Kdn represents 3-deoxy-D-glycero-D-galacto-nonulsonic acid and GalNAc-ol is N-acetylgalactosaminitol: [sequence: see text] As shown for five other amphibian species, the structures of these carbohydrate chains appear to be species specific and can afford a basis for molecular taxonomy. These new sequences also reflect the occurrence of specific fucosyltransferase activities that are characteristic of Ambystoma maculatum.

The glycan moiety of human pancreatic lithostathine. Structure characterization and possible pathophysiological implications

Lithostathine, also known as pancreatic stone protein, pancreatic thread protein or regenerating protein, is a glycoprotein which is normally found in the exocrine pancreas, whereas in other tissues it appears either only under pathological conditions, such as Alzheimer's disease (brain), cancer (colon) or during regeneration (endocrine pancreas). In the latter case, it has been shown recently that it acts as a growth factor which stimulates islet regeneration. Little is known about its glycan moiety, which conceivably might be involved in this tissue specificity and pathophysiological characteristics. Therefore we isolated the major oligosaccharide chains of human pancreatic lithostathine and determined their sequences by means of NMR analysis. We obtained eleven different glycoforms and we were able to determine the sequence of seven of them. They all were from the same site of glycosylation (Thr5) and displayed the same core 2 structure: GlcNAc(beta 1-6)[Gal(beta 1-3)]GalNAc alpha-. They ranged in size from 4 to 9 sugar residues. Elongation was found to proceed from a common tetrasaccharidic core: Gal(beta 1-4)GlcNAc(beta 1-6)[Gal(beta 1-3)]GalNAc-ol through N-acetyllactosamine units. The non-reducing ends of some oligosaccharides carry the antigenic determinant H, with presence of external Fuc linked only in (alpha 1-2) to Gal. All the glycans, except one, carry a sialic acid in (alpha 2-3) linkage to Gal, with one disialylated form which displays a supplementary (alpha 2-6) linkage. These findings are consistent with the polymorphism of the protein, shown by means of SDS gel electrophoresis and isoelectric focusing, either in its native form or after enzymic processing. Moreover, sialylation seems to protect to some extent the Arg11-Ile12 bond from in situ hydrolysis, thus preventing the harmful precipitation of the C-terminal polypeptide in the pancreatic ducts.

Beta-1,2-linked oligomannosides from Candida albicans act as signals for tumor necrosis factor alpha production

Different cell wall components from Candida albicans have been shown to stimulate murine macrophages for tumor necrosis factor alpha (TNF-alpha) secretion. All of these molecules contain beta-1,2-oligomannosides. In order to examine their role in TNF-alpha production, acid-labile oligosaccharides, released from C. albicans VW32 cell wall phosphopeptidomannan by mild acid hydrolysis, and previously shown to correspond to homopolymers of beta-1,2-linked mannopyranosyl units, were separated by gel filtration chromatography according to their degree of polymerization. Murine macrophages incubated with purified oligomannosides (M2 to M8) released TNF-alpha to an extent which was dependent on, although not directly correlated with, the length of the mannosyl chain. Slight activity was observed with M4 and M5; M6 and M7 had virtually no effect, whereas M8 was associated with strong TNF-alpha release. This effect of M8 was dose dependent and was not altered by polymyxin B, known to interfere with lipopolysaccharide-induced TNF-alpha production. These results suggest that stimulation of TNF-alpha release by C. albicans glycoconjugates containing beta-1,2-linked oligomannosides may be due, at least in part, to the presence of these components.

First evidence of human meconium glycoasparagines

During a systematic study of carbohydrate material present in human meconium, in addition to the previously described mucins, glycolipids and free oligosaccharides, we have now characterized a significant quantity of free glycoasparagines. These glycoasparagines have been isolated from human meconium by a combination of ion-exchange, concanavalin A (ConA)-affinity and high-performance liquid (HPLC) chromatographies. Their structures have been established by 400 MHz 1H-NMR spectroscopy. These compounds are related to N-acetyllactosaminic type structures and are based on the common core: [formula: see text] These glycoasparagines are probably derived from both protease and partial exoglycosidase hydrolysis of fetal gastrointestinal N-glycosyl proteins. Their structures are discussed in the context of the known catabolic pathways of N-glycans.

Rat mammary-gland transferrin: nucleotide sequence, phylogenetic analysis and glycan structure

The complete cDNA for rat mammary-gland transferrin (Tf) has been sequenced and also the native protein isolated from milk in order to analyse the structure of the main glycan variants present. A lactating-rat mammary-gland cDNA library in lambda gt10 was screened with a partial cDNA copy of rat liver Tf and subsequently rescreened with 5' fragments of the longest clones. This produced a 2275 bp insert coding for an open reading frame of 695 amino acid residues. This includes a 19-amino acid signal sequence and the mature protein containing 676 amino acids and one N-glycosylation site in the C-terminal domain at residue 490. Phylogenetic analysis was carried out using 14 translated Tf nucleotide sequences, and the derived evolutionary tree shows that at least three gene duplication events have occurred during Tf evolution, one of which generated the N- and C-terminal domains and occurred before separation of arthropods and chordates. The two halves of human melanotransferrin are more similar to each other than to any other sequence, which contrasts with the pattern shown by the remaining sequences. Native rat milk Tf is separated into four bands on native PAGE that differ only in their sialic acid content: one biantennary glycan is present containing either no sialic acid residues or up to three. The complete structures of the two major variants were determined by methylation, m.s. and 400 MHz 1H-n.m.r. spectroscopy. They contain either one or two neuraminic acid residues (alpha 2-->6)-linked to galactose in conventional biantennary N-acetyl-lactosamine-type glycans. Most contain fucose (alpha 1-->6)-linked to the terminal non-reducing N-acetylglucosamine.

Use of a water flip-back pulse in the homonuclear NOESY experiment

A simple modification to the WATERGATE water suppression scheme [Piotto, M., Saudek, V. and Sklenář, V. (1992) J. Biomol. NMR, 2, 661-665] is proposed. Radiation damping is used as an active element during the mixing time of a NOESY experiment, in order to obtain a reproducable state of the water magnetization at the end of the mixing time. Through the use of a water flip-back pulse and a gradient-tailored excitation scheme, we obtain both an excellent water suppression and a water magnetization close to equilibrium at the beginning of the acquisition time. We show experimentally that this modification results in a 20% gain in intensity for all signals when using a relaxation delay of 1.5 s, and also that avoiding a semisaturated state for the water magnetization allows the amide protons as well as other proton resonances to relax to equilibrium with their proper relaxation time.

Native like structure and stability of apo AI in a n-propanol/water solution as determined by 13C NMR

To elucidate the molecular details of the conformation of apolipoprotein AI (apo AI), we have developed an approach related to the solubilization of this protein in 30% n-propanol. We have previously reported the promotion of a native-like structure for apo AI solubilized in n-propanol, as depicted by circular dichroism, fluorescence, and limited proteolytic digestion as compared to the lipid associated form of apo AI. In the present study, we labeled the Lys residues of apo AI with 13C by reductive methylation and used 13C NMR to confirm the formation of a native-like structure of apo AI in this environment. Furthermore, by the above criteria (circular dichroism and 13C NMR) and by using urea and temperature as denaturing agents, we show that the denaturation of the native-like structure of apo AI in n-propanol is a biphasic process. These studies show that in 30% n-propanol, apo AI contains two independently folded structural domains, of markedly different stabilities that might correspond to the amino-terminal and the carboxy-terminal halves of the molecule.

Primary structure of 12 neutral oligosaccharide-alditols released from the jelly coats of the anuran Xenopus laevis by reductive beta-elimination

The O-linked oligosaccharides of the jelly coat surrounding the eggs of Xenopus laevis were analysed by 1H-NMR spectroscopy. Among the 12 neutral oligosaccharide-alditols which have been characterized, three of them possess the following unusual structures: [sequence: see text] As previously observed for six other amphibian species, the carbohydrate chains of the jelly coat of Xenopus eggs display a high species specificity which could support a biological role during the fertilization processes.

Structure of three Kdn-containing oligosaccharide-alditols released from oviducal secretions of Ambystoma tigrinum: characterization of the carbohydrate sequence Fuc (alpha 1-5) [Fuc (alpha 1-4)] Kdn (alpha 2-3/6)

Oligosaccharide-alditols released by reductive beta-elimination from the egg jelly coat of Ambystoma tigrinum were analyzed by 1H NMR spectroscopy. As observed for five other amphibian species, these carbohydrate chains are highly species-specific, and should support the species-specificity of gamete interaction. The carbohydrate chains of Ambystoma tigrinum are characterized by the presence of a new type of sequence: Fuc (alpha 1-5) [(Fuc (alpha 1-4)] Kdn (alpha 2-3/6).

Chemical and immunological characterization of the extracellular galactomannan of Aspergillus fumigatus

The galactomannan (GM) produced extracellularly by Aspergillus fumigatus has been purified by a double sequential hydrazine-nitrous acid treatment of the ethanol precipitate of the culture filtrate. Nuclear magnetic resonance and gas-liquid chromatography-mass spectrometry analysis have been performed on intact GM, acid-hydrolyzed GM, and oligomers resulting from the acetolysis of the acid-hydrolyzed GM. Results show that A. fumigatus GM is composed of a linear mannan core with an alpha-(1-2)-linked mannotetraose repeating unit attached via alpha-(1-6) linkage. Side chains composed of an average of 4 to 5 beta-(1-5)-galactofuranose units are linked to C-6 and C-3 positions of alpha-(1-2)-linked mannose units of the mannan. The immunoreactivity of GM and HCl-hydrolyzed GM was studied by use of human sera from aspergillosis patients and an antigalactofuran monoclonal antibody. The alpha-(1-2) (1-6)-mannan core is not antigenic. The immunogenic galactofuran is found amongst several exocellular glycoproteins. According to a direct enzyme-linked immunosorbent assay with GM as the detector antigen, only 26% of the serum samples from aspergilloma patients (all positive by immunodiffusion assays) give optical density values superior to a cutoff estimated as the mean +/- 3 standard deviations of values obtained with control sera.

Toward an understanding of the biogenesis of the starch granule. Determination of granule-bound and soluble starch synthase functions in amylopectin synthesis

Plant starch synthesis can be distinguished from those of bacterial, fungal, and animal glycogen by the presence of multiple elongation (starch synthases) and branching enzymes. This complexity has precluded genetic assignment of functions to the various soluble starch synthases in the building of amylopectin. In Chlamydomonas, we have recently shown that defects in the major soluble starch synthase lead to a specific decrease in the amount of a subset of amylopectin chains whose length ranges between 8 and 40 glucose residues (Fontaine, T., D'Hulst, C., Maddelein, M.-L., Routier, F., Marianne-Pepin, T., Decq, A., Wieruszeski, J. M., Delrue, B., Van Den Koornhuyse, N., Bossu, J.-P., Fournet, B., and Ball, S. G. (1993) J. Biol. Chem. 268, 16223-16230). We now demonstrate that granule-bound starch synthase, the enzyme that was thought to be solely responsible for amylose synthesis, is involved in amylopectin synthesis. Disruption of the Chlamydomonas granule-bound starch synthase structural gene establishes that synthesis of long chains by this enzyme can become an absolute requirement for amylopectin synthesis in particular mutant backgrounds. In the sole presence of soluble starch synthase I, Chlamydomonas directs the synthesis of a major water-soluble polysaccharide fraction and minute amounts of a new type of highly branched granular material, whose structure is intermediate between those of glycogen and amylopectin. These results lead us to propose that the nature of the elongation enzyme conditions the synthesis of distinct size classes of glucans in all starch fractions.

Change in glycosylation of chicken transferrin glycans biosynthesized during embryogenesis and primary culture of embryo hepatocytes

Transferrins were isolated by immunoaffinity chromatography from chicken serum, chicken embryo serum and from the culture medium of chicken embryo hepatocytes in primary culture. The glycovariants of these three transferrins were separated by ion-exchange chromatography using a fast protein liquid chromatography (FPLC) system. The structures of the oligosaccharide-alditols released by hydrazinolysis from the glycovariants were compared after analysis by a combination of methanolysis, methylation analysis and 1H-NMR spectroscopy. In the three transferrins analysed, the oligosaccharides were of the biantennary N-acetyllactosaminic type, having several prominent features. In particular, the embryo serum transferrin glycan differed from that of chicken serum transferrin by the presence of a bisecting N-acetylglucosamine, suggesting a developmental change in glycosylation. The glycan structure of the transferrin secreted by the embryo hepatocytes in primary culture was marked by the presence of fucose (alpha 1-6) linked to the core N-acetylglucosamine, suggesting that expression of the fucosyltransferase activity is dependent on cell culture conditions. Moreover, comparative analysis of chicken serum transferrin and ovotransferrin glycans reinforces the idea that the glycosylation of two identical polypeptide chains is organ specific.

Structure of the major neutral oligosaccharide-alditols released from the egg jelly coats of Axolotl maculatum. Characterization of the carbohydrate sequence GalNAc(beta 1-4)[Fuc(alpha 1-3)] GlcNAc(beta 1-3/6)

Several O-linked oligosaccharides of the jelly coat surrounding the eggs of Axolotl maculatum were analysed by 1H-NMR spectroscopy. The four major oligosaccharidealditols released by reductive beta-elimination display either the Lewisx (Lex) determinant or the sequence GalNAc(beta 1-4)[Fuc(alpha 1-3)]GlcNAc. This last structure has previously been characterized in allergenically active oligosaccharides isolated from the sea squirt H-antigen, and in the N-linked glycans of Schistosoma mansoni and human urokinase. It represents the major carbohydrate chain found in A. maculatum, the oviduct of which constitutes an excellent source of beta 1-4-acetylgalactosaminyl transferase activity. Moreover, the carbohydrate chains isolated from A. maculatum are quite different from those found in seven other amphibian species, in which the presence of species-specific material has been characterized. The role of carbohydrates appears more and more apparent during the fertilization process, and the diversity of the O-linked oligosaccharides supports such a biological role.

Sialylation and sulfation of the carbohydrate chains in respiratory mucins from a patient with cystic fibrosis

Mucin glycopeptides were prepared from the sputum of a patient suffering from cystic fibrosis. The carbohydrate chains were released by alkaline borohydride treatment. Sialylated and sulfated oligosaccharide-alditols were purified by ion-exchange chromatography, gel filtration, and high performance anion-exchange chromatography. The structures of the oligosaccharide-alditols were determined by high resolution 1H NMR spectroscopy in combination with fast atom bombardment-mass spectrometry. Twenty-four oligosaccharides were characterized and illustrate the diversity of the carbohydrate chains of cystic fibrosis respiratory mucins. Among these 24 oligosaccharide-alditols, 15 are novel structures. Sialylation may occur on the C-6 of the N-acetylgalactosamine involved in the carbohydrate-peptide linkage or on a terminal galactose residue, either on C-3 or on C-6. Sulfation may occur either on the C-3 of a terminal galactose residue or on the C-6 of a N-acetylglucosamine residue. The most complex structures contain sulfated derivatives of the H,X, or Y determinants or a sialylated and sulfated derivative of the X determinant (Structure A).

Soluble forms of alpha-D-mannosidases from rat liver. Separation and characterization of two enzymic forms with different substrate specificities

We have previously reported the substrate specificity of the rat liver cytosolic alpha-D-mannosidase [Haeuw, J. F., Strecker, G., Wieruszeski, J. M., Montreuil, J. & Michalski, J.-C. (1991) Eur. J. Biochem. 202, 1257-1268]. Here, we report the characterization and the purification of this alpha-D-mannosidase and the presence of two soluble forms of alpha-D-mannosidases from rat liver. The cytosolic alpha-D-mannosidase was purified nearly 660-fold with 2.66% recovery to a state approaching homogeneity using: (a) (NH4)2SO4 precipitation; (b) concanavalin-A-Sepharose chromatography; (c) affinity chromatography on a cobalt-chelating Sepharose column; (d) ion-exchange (DEAE-trisacryl M) column chromatography; (e) molecular-size chromatography (Sephacryl S 200). The enzyme was eluted from the final column at an apparent molecular mass of 113 kDa. SDS/PAGE analysis yielded a major protein band at 108 kDa. Moreover, the purification allowed to distinguish two mannosidase activities with different kinetic properties. The first cytosolic activity retained on the cobalt-chelating column was optimally active at neutral pH, was activated by Co2+, was strongly inhibited by swainsonine (Ki = 3.7 microM) but not by deoxymannojirimycin and was active with p-nitrophenyl alpha-D-mannoside (Km = 0.072 mM). Man9GlcNAc was hydrolysed by the purified enzyme down to a Man5GlcNAc structure, i.e. Man(alpha 1-2)Man(alpha 1-2)Man(alpha 1-3)[Man(alpha 1-6)]Man(beta 1-4) GlcNA c, which represents the Man5 oligosaccharide chain of the dolichol pathway formed in the cytosolic compartment during the biosynthesis of N-glycosylprotein glycans. The second activity not retained on the cobalt-chelating column was optimally active at neutral pH, was inhibited by swainsonine (Ki = 28.4 microM) but not by deoxymannojirimycin and was active with p-nitrophenyl alpha-D-mannoside (Km = 0.633 mM). Man9GlcNAc was broken by this enzymic activity down to Man8GlcNAc and Man7GlcNAc structures. Similitaries with endoplasmic reticulum alpha-D-mannosidase exist and this enzyme could be the cytosolic form of the endoplasmic reticulum alpha-D-mannosidase.

Bi-antennary oligo-(N-acetyllactosamino)glycans of I-type are galactosylated preferentially at the GlcNAc beta 1-6Gal linked arms by alpha 1,3-galactosyltransferase of bovine thymus

alpha 1,3-Galactosylation of radiolabelled bi-antennary acceptors Gal beta 1-4GlcNAc beta 1-3(Gal beta 1-4GlcNAc beta 1-6)Gal-R (R = 1-OH, beta 1-4GlcNAc or beta 1-4Glc) with bovine thymus alpha 1,3-galactosyltransferase was studied. At all stages of the reactions the three acceptors reacted faster at the 1-->6 linked arm than at the 1-->3 linked branch. Hence, in addition to the doubly alpha 1,3-galactosylated products, practically pure Gal beta 1-4GlcNAc beta 1-3(Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-6)Gal-R could be obtained from the three acceptors in reactions that had proceeded to near completion. The isomeric mono-alpha 1,3-galactosylated products were identified by using exoglycosidases to remove the branches unprotected by alpha 1,3-galactoses and by subsequently identifying the resulting linear glycans chromatographically.

Toward an understanding of the biogenesis of the starch granule. Evidence that Chlamydomonas soluble starch synthase II controls the synthesis of intermediate size glucans of amylopectin

Low starch mutants of Chlamydomonas reinhardtii were isolated after x-ray mutagenesis of wild-type strain 137C. The mutants accumulated 20-40% of the normal amount and displayed a 2-fold decrease of the total glycogen-primed soluble starch synthase activity. Three different mutant alleles of the st-3 gene were isolated that were characterized by similar defects and displayed a net increase in amylose content. Amylose-primed synthesis of glucan in native gels revealed a complete wipe out of one of the soluble starch synthases. Zymograms and kinetic analyses performed both in the mutant and in partially purified wild type extracts reveal at least two distinct activities that are partly analogous to higher plant soluble starch synthases I and II (SSI and II). The st-3 mutants were defective for SSII. Methylation and debranching of the purified amylopectin fraction clearly show a decrease in the number of intermediate size glucans (dp8 to 50) and an absolute and relative increase of very short glucans (dp2 to 7). These results suggest that a soluble starch synthase may be necessary for the synthesis or maintenance of intermediate size glucans that are the main component of the branched clusters of amylopectin.

Primary structure of human milk octa-, dodeca- and tridecasaccharides determined by a combination of 1H-NMR spectroscopy and fast-atom-bombardment mass spectrometry. Evidence for a new core structure, the para-lacto-N-octaose

Two octasaccharides, two dodecasaccharides and a tridecasaccharide have been isolated from human milk by a combination of paper chromatography, high-performance liquid chromatography and high-performance anion-exchange chromatography. Their structural analysis investigated by 400-MHz 1H- and 13C-NMR spectroscopy and by mass spectrometry led to the following structures. [formula: see text] The two octasaccharides have been previously characterized in human milk; the complete assignment of the 1H and 13C spectra is reported here. One of the dodecasaccharides is a tetrafucosyl derivative with a new core: typeI-(beta 1-3)-typeII-(beta 1-3)-typeII-(beta 1-3)-Gal((beta 1-4)Glc, where typeI = Gal(beta 1-3)GlcNAc and typeII = Gal(beta 1-4)GlcNAc. These oligosaccharides display simultaneously Lewis(b) and Lewis(x) determinants or Lewis(a), Lewis(b) and Lewis(x) determinants.

Isolation and characterisation of hemicelluloses from sunflower hulls

The hemicelluloses extracted from sunflower hulls by repeated alternating oxidative and alkaline treatments were purified by precipitation with Cetavlon and then ion-exchange chromatography on DEAE-trisacryl. The resulting fractions were examined by hydrolysis, methylation, GLC-MS, and NMR spectroscopy. The hemicelluloses are of the glucuronoxylan type with the following structure -->4)-beta-D-Xylp-(1-->4)-[4-O-Me-alpha-D-GlcpA-(1-->2)]-bet a-D-Xylp-(1-->. The polysaccharides differed in the amount of branching; the ratio of the main fraction 4-O-MeGlcA:Xyl was 1:8-9.

Complete 1H- and 13C-resonance assignments for D-mannooligosaccharides of the beta-D-(1-->2)-linked series released from the phosphopeptidomannan of Candida albicans VW.32 (serotype A)

D-Mannooligosaccharides (dp 1 to > 17) were released by mild acid hydrolysis from the phosphopeptidomannan of a Candida albicans strain of A serotype (VW.32). Among these, mannooligosaccharides ranging from bi- to hepta-ose, which were obtained in appreciable amounts, were structurally investigated and found to belong to the beta-D-(1-->2)-linked series. The occurrence of such compounds has already been reported in other Candida albicans strains. The complete 1H- and 13C-resonance assignments for manno-tri- to manno-hepta-ose are reported and general rules applicable for the 1NMR spectrum analysis of linear mannooligosaccharide of the general structure, beta-D-Man p-(1-->2)-[beta-D-Man p-(1-->2)]n-beta-D-Man p are proposed.

Structural analysis of the carbohydrate chains isolated from mistletoe (Viscum album) lectin I

Two glycopeptide fractions prepared from mistletoe (Viscum album) lectin I by Pronase digestion were fractioned by affinity chromatography on a concanavalin A-Sepharose column. With 400-MHz 1H NMR spectroscopy, in conjunction with sugar analysis, the following oligosaccharide structures could be determined: two oligomannose-type glycans in the ratio 4:1, one containing six mannose and the other containing five mannose units, both with two 2-acetamido-2-deoxyglucose units. In addition, a mannotriosyl-->N,N'-diacetylchitobiose glycan containing a xylosyl group and an alpha-fucosyl group (1-->3)-linked to the 2-acetamido-2-deoxyglycosyl-1 residue, a common core element of many plant glycoproteins, was also observed.

Heterogeneity of bovine lactotransferrin glycans. Characterization of alpha-D-Galp-(1-->3)-beta-D-Gal- and alpha-NeuAc-(2-->6)-beta-D-GalpNAc-(1-->4)- beta-D-GlcNAc-substituted N-linked glycans

Lactotransferrin isolated from a pool of mature bovine milk has been shown to contain N-glycosidically-linked glycans possessing N-acetylneuraminic acid, galactose, mannose, fucose, N-acetylglucosamine, and N-acetylgalactosamine. The glycopeptides obtained by Pronase digestion were fractionated by concanavalin A-Sepharose affinity chromatography into three fractions: slightly retained (A), retained (B), and strongly retained (C). The structure of the glycans of the three fractions has been determined by application of methanolysis, methylation analysis, fast atom bombardment-mass spectrometry, and 1H NMR spectroscopy. Diantennary structures without GalNAc were present as partially sialylated and partially (1-->6)-alpha-L-fucosylated structures in Fractions A and B. Sequences containing alpha-D-Galp-(1-->3)-beta-D-Gal on the alpha-D-Man-(1-->6) antenna, and beta-D-GalpNAc-(1-->4)-beta-D-GlcNAc and alpha-NeuAc-(2-->6)-beta-D-GalpNAc-(1-->4)-beta-D-GlcNAc on the alpha-D-Man-(1-->3) antenna were characterized in the oligosaccharide-alditols obtained by reductive cleavage of Fraction B. A series of Man4-9-GlcNAc structures were identified in Fraction C after endo-N-acetyl-beta-D-glucosaminidase digestion. These results show that the structures of bovine lactotransferrin glycans are more heterogeneous than those of previously characterized transferrin glycans.

1H-and 13C-n.m.r. spectroscopy of 2-oxo-3-deoxy-D-glycero-D- galactononulosonic acid-containing oligosaccharide-alditols bearing Lewis X, Lewis Y and A-Lewis Y determinants isolated from the jelly coat of Pleurodeles waltl eggs

Three acidic oligosaccharide-alditols carrying Lewis X, Lewis Y and A-Lewis Y determinants were isolated from the jelly coat of Pleurodeles waltl eggs. These compounds possess the following structures. Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3[2-oxo-3-deoxy-D- glycero-D-galactononulosonic acid (KDN)alpha 2-6] GalNAc-ol; Fuc alpha 1-2Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3(KDN alpha 2-6) GalNAc-ol and Fuc alpha 1-2(GalNAc alpha 1-3)Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3(KDN alpha 2-6)GalNAc-ol. The complete 1H-n.m.r.-spectrum assignment for the three compounds and the 13C-n.m.r. analysis of the A-Lewis Y determinant-containing heptasaccharide are reported.

Oligosaccharide structures of mucins secreted by the human colonic cancer cell line CL.16E

Cl.16E, a stably differentiated clonal derivative of the human colonic cancer cell line HT29, was used to investigate the structure of oligosaccharide chains of mucins in colonic cancer. Secretory mucins were purified by equilibrium density gradient centrifugation in CsCl. Oligosaccharide side chains were isolated after beta-elimination. Compositional analysis of oligosaccharide-alditols performed after purification by gel filtration on a Bio-gel P-6 column showed 1) that GalNAc residues were located exclusively at the reducing ends of the chains, and 2) that fucose was absent from the preparation. Oligosaccharide-alditols were separated by high performance liquid chromatography (HPLC) on quaternary amine packings into a minor neutral fraction representing about 6.5% by weight of released oligosaccharides and four acidic fractions. Two acidic fractions, namely FI and FII encompassing mono- and disialylated structures, respectively, and containing 78% of total oligosaccharide alditols, were separated by HPLC. Structural determinations were carried out using methylation analysis, 1H NMR spectroscopy, and fast atom bombardment-mass spectrometry. Twelve oligosaccharide structures were determined which ranged in size from 3 to 8 residues. These oligosaccharides were based on core types 1, 2, and 4. Elongation of oligosaccharide chains was terminated by addition of sialic acid in alpha 2-3 linkage to Gal beta 1-3R and to Gal beta 1-4R residues. The predominant structure was a hexasaccharide (fraction FII-4). This contrasts with normal colonic mucins whose oligosaccharides were previously found to be based on core 3 structures and carry sialic acids in alpha (2-6) linkage to Gal beta 1-3R, to Gal beta 1-4R, and to GalNAc alpha-R (Podolsky, D.K. (1985) J. Biol. Chem. 260, 8262-8271; Podolsky, D.K. (1985) J. Biol. Chem. 260, 15510-15515). Collectively our findings suggest that Cl.16E colon cancer cells are able to synthesize mucin oligosaccharides of gastric type whose elongation is truncated by premature sialylation.