Structural characterisation of galactoglucomannan secreted by suspension-cultured cells of Nicotiana plumbaginifolia

Galactoglucomannan (GGM) from cultures of Nicotiana plumbaginifolia has Man:Glc:Gal:Ara:Xyl in 1.0:1.1:1.0:0.1:0.04 ratio. Linkage analysis contained 4- and 4,6-Manp, 4-Glcp, terminal Galp and 2-Galp, small amounts and terminal Arap and terminal Xylp, and approximately 0.03 mol acetyl per mol of glucosyl residue. Treatment with alpha- and beta-D-galactosidases showed that the majority of the side-chains were either single Galp-alpha-(1-->residues or the disaccharide Galp-beta-(1-->2)-Galp-alpha-(1-->linked to O-6 of the 4-Manp residues of the glucomannan backbone. Analysis of the oligosaccharides generated by endo-(1-->4)-beta-mannanase digestion confirmed that the GGM comprises a backbone of predominantly alternating-->4)-D-Manp-beta-(1-->and-->4)-D-Glcp-beta-(1-->branch ed at O-6 of 65% of the 4-Manp residues. The major oligosaccharide identified was D-Glcp-beta-(1-->4)-[D-Galp-beta-(1-->2)-D-Galp-alpha-(1-->6)]-D-Man p-beta-(1-->4)-D-Glcp-beta-(1-->4)-[D-Galp-alpha-(1-->6)]-D-Manp -beta-(1-->(27%), and most of the other oligosaccharides produced in significant quantities were based on this structure.

Activation of pollen tube callose synthase by detergents. Evidence for different mechanisms of action

In pollen tubes of Nicotiana alata, a membrane-bound, Ca(2+)-independent callose synthase (CalS) is responsible for the biosynthesis of the (1,3)-beta-glucan backbone of callose, the main cell wall component. Digitonin increases CalS activity 3- to 4-fold over a wide range of concentrations, increasing the maximum initial velocity without altering the Michaelis constant for UDP-glucose. The CalS activity that requires digitonin for assay (the latent CalS activity) is not inhibited by the membrane-impermeant, active site-directed reagent UDP-pyridoxal when the reaction is conducted in the absence of digitonin. This is consistent with digitonin increasing CalS activity by the permeabilization of membrane vesicles. A second group of detergents, including 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate (CHAPS), Zwittergent 3-16, and 1-alpha-lysolecithin, activate pollen tube CalS 10- to 15-fold, but only over a narrow range of concentrations just below their respective critical micellar concentrations. This activation could not be attributed to any particular chemical feature of these detergents. CHAPS increases maximum initial velocity and decreases the Michaelis constant for UDP-glucose and activates CalS even in the presence of permeabilizing concentrations of digitonin. Inhibition studies with UDP-pyridoxal indicate that activation by CHAPS occurs by recruitment of previously inactive CalS molecules to the pool of active enzyme. The activation of pollen tube CalS by these detergents therefore resembles activation of the enzyme by trypsin.

War injuries of the lungs

OBJECTIVE

The authors' experience in the treatment of war injuries of the lungs, gained during the war in Croatia, from August 25, 1991 until July 1, 1995, is presented. In that period, 424 patients with injuries of the lungs were treated at the Split Clinical Hospital.

METHODS

The paper is a retrospective study of 424 wounded persons with lung injuries gained during the war in Croatia, processed by basic statistical analysis.

RESULTS

Penetrating and nonpenetrating wounds were present in 331 (78.1%) and 93 (21.9%) patients, respectively. There were 407 (96.0%) men and 17 (4.0%) women. Explosive wounds were most frequent (n = 251; 59.2%), followed by gunshot wounds (n = 158: 37.3%) and other types of wounds in 15 (3.5%) patients only. Thoracotomy was performed in 89 (22.9%) patients, whereas conservative surgical methods (wound treatment, chest-tube drainage, appropriate fluid therapy, antimicrobial and atelectasis prophylaxis) were used in 300 (77.1%) patients. A great majority of the patients (n = 395; 93.2%) were discharged as fully recovered or in improved condition, 22 (5.2%) patients were referred to other institutions for further treatment, and seven (1.7%) wounded persons died.

CONCLUSIONS

It is shown that most war wounds of the lungs can be successfully managed by 'conservative' surgical treatment.

Sulfated galactans from Australian specimens of the red alga Phacelocarpus peperocarpos (Gigartinales, Rhodophyta)

Polysaccharides from the red alga Phacelocarpus peperocarpos were extracted with hot water, clarified, and precipitated with 2-propanol. The native preparation was highly sulfated (36.2% w/w). Alkali modification decreased the sulfate content by 2.0% w/w. The alkali-modified polysaccharide is composed mostly of galactose (Gal. 51 mol%) and 3,6-anhydrogalactose (AnGal, 41 mol%), with minor amounts of a mono-O-methylgalactose (MeGal, 1 mol%), xylose (Xyl, 6 mol%), and glucose (Glc, 1 mol%). The FTIR spectrum of the alkali-modified polysaccharide resembled kappa-carrageenan with absorption at 930 cm-1 (indicative of AnGal) and 850 cm-1 (Gal 4-sulfate). However, an additional, major band of absorption occurred sulfate ester substitution at O-6 of at 820 cm-1, indicating the presence of equatorial sulfate ester substitution at O-6 of Gal residues. A combination of linkage and 13C NMR spectroscopic analyses showed that the polysaccharide was composed predominantly of a novel repeating-unit, O-beta-D-galactopyranosyl 4,6-disulfate)-(1-->4)-3,6-anhydro-alpha-D-galactopyranose. Minor structural variations also occurred, including alternative patterns of sulfation and the presence of terminal Xylp. The location of the terminal Xylp residues was not certain but evidence supported their attachment at O-3 of some 4-linked Galp residues. The cell-wall galactans remain unchanged during the life cycle of the alga.

Disulphide bonding in a stylar self-incompatibility ribonuclease of Nicotiana alata

Many flowering plants have developed a self-incompatibility mechanism, which is controlled by a single polyallelic locus (the S-locus), to prevent inbreeding. The products of the S-locus in the styles of solanaceous plants are an allelic series of glycoproteins with RNase activity [McClure, B. A., Haring, V., Ebert, P. R., Anderson, M. A., Simpson, R. J., Sakiyama, F. & Clarke, A. E. (1989) Nature 342, 955-957]. These S-RNases show some amino-acid-sequence similarity with two fungal RNases (T2 and Rh), including the presence of two active-site His residues, which suggests a common three-dimensional structure. Disulphide bonding is important in the maintenance of the three-dimensional structure of the fungal RNases [Kurihara, H., Mitsui, Y., Ohgi, K., Irie, M., Mizuno, H. & Nakamura, T. (1992) FEBS Lett. 306, 189-192] and the S-RNases [Tsai, D. S., Lee, H.-S., Post, L. C., Kreiling, K. M. & Kao, T.-H. (1992) Sex. Plant Reprod. 5, 256-263]. We have used the S2-allele RNase of Nicotiana alata, which has nine Cys residues, to establish the pattern of disulphide bonding. The disulphide bonds Cys16-Cys21, Cys45-Cys94, Cys153-Cys182 and Cys165-Cys176 are consistent with the S2-RNase having a similar three-dimensional structure to RNase Rh. A free Cys residue (Cys95) adjacent to Cys45-Cys94 promotes a rapid specific disulphide migration when the protein is exposed to denaturing conditions.

Arabinogalactan-proteins: a class of extracellular matrix proteoglycans involved in plant growth and development

Arabinogalactanproteins (AGPs) are proteoglycans of the extracellular matrix o f most plants. Since the late 1980s, AGPs have attracted widespread attention from plant biologists following reports of their involvement in plant development. In particular, the use of monoclonal antibodies to carbohydrate epitopes of AGPs has demonstrated stage- and tissue-specificity and has led to suggestions that they are involved in tissue morphogenesis. The recent cloning of the genes for several AGP protein backbones allows us to consider new strategies to address their function. Here, we summarize our knowledge of AGPs and consider parallels with animal proteoglycans as a possible framework for future work.

Structural characterisation of xyloglucan secreted by suspension-cultured cells of Nicotiana plumbaginifolia

Linkage analysis of a xyloglucan from the extracellular medium of suspension cultures of Nicotiana plumbaginifolia showed mostly 4-Glcp and 4,6-Glcp, terminal Xylp and 2-Xylp, and terminal Araf, along with approximately 10% (w/w) O-acetyl groups, equivalent to approximately 0.28 mol acetyl per mol of glycosyl residue. Methylation with methyl trifluoromethanesulfonate under neutral conditions, followed by re-methylation with CD3I under basic conditions, and conversion into partially methylated alditol acetates showed that O-acetyl groups were primarily attached to C-6 of approximately 44% of the 4-Glcp backbone not substituted with Xylp residues and to C-5 of approximately 15% of the terminal Araf residues. These positions of the O-acetyl groups were confirmed by 1H-NMR. Oligosaccharides generated by digestion of native xyloglucan with endo-(1-->4)-beta-glucanase were separated by a combination of gel-filtration chromatography and anion-exchange HPLC, and analysed by glycosyl linkage analysis and by electrospray ionisation-mass spectrometry (ESI-MS). The major oligosaccharide subunits were Glc4Xyl2 and Glc5Xyl2, of which 50-60% are substituted with one terminal Araf residue attached to O-2 of a Xylp residue, and a further 20-25% are substituted with two terminal Araf residues attached to O-2 of the Xylp residues. ESI-MS showed that many of the oligosaccharide subunits carried one, two, and, occasionally three O-acetyl groups.

Structure of N-glycans on the S3- and S6-allele stylar self-incompatibility ribonucleases of Nicotiana alata

Self-incompatibility is a mechanism developed by many plants to prevent inbreeding. The products of the self-incompatibility (S)-locus in the styles of solanaceous plants are a series of glycoproteins with ribonuclease activity. In this study, we report on the N-glycans from the stylar self-incompatibility S3- and S6-ribonucleases of Nicotiana alata, which were enzymically released and fractionated by high-pH anion-exchange HPLC. A total of 14 N-glycans were identified and characterized by a combination of electrospray-ionization mass-spectrometry, 1H-NMR spectros-copy, chemical degradation, and methylation analyses. This patterns of N-glycosylation is much more complex than that previously found on the N.alata S1- and S2-RNases, each of which contained only four N-glycans.

Purification and structural characterization of a filamentous, mucin-like proteophosphoglycan secreted by Leishmania parasites

Parasitic protozoa of the genus Leishmania secrete a filamentous macromolecule that forms networks and appears to be associated with cell aggregation. We report here the purification of this parasite antigen from Leishmania major culture supernatant and its compositional (75.6% carbohydrate, 20% phosphate, 4.4% amino acids, w/w), structural, and ultrastructural characterization as a highly unusual proteophosphoglycan (PPG). Mild acid hydrolysis, which cleaves preferentially hexose 1-phosphate bonds, releases the PPG glycans. Their structures are Galbeta1-4Man, Manalpha1-2Man, Galbeta1-3Galbeta1-4Man, PO4-6(Galbeta1-3)0-2Galbeta1-4Man, and PO4-6(Arabeta1-2Galbeta1-3)Galbeta1-4Man. These glycans are also components of the parasite glycolipid lipophosphoglycan, but their relative abundance and structural organization in PPG are different. Some of them represent novel forms of protein glycosylation. 31P NMR on native PPG demonstrates that phosphate is exclusively in phosphodiester bonds and that the basic structure R-Manalpha1-PO4-6-Gal-R connects the glycans. A phosphodiester linkage to phosphoserine (most likely R-Manalpha1-PO4-Ser) anchors the PPG oligosaccharides to the polypeptide. PPG has a unique amino acid composition; glycosylated phosphoserine (>43 mol %), serine, alanine, and proline account for more than 87 mol % and appear to be clustered in large proteinase-resistant domains. Electron microscopy of purified PPG reveals cable-like, flexible, long (to 6 microm), and unbranched filaments. The overall structure of PPG shows many similarities to mammalian mucins. Potential functions of this novel mucin-like molecule for the parasites are discussed.

Biosynthesis of lipophosphoglycan from Leishmania major: solubilization and characterization of a (beta 1-3)-galactosyltransferase

Lipophosphoglycan (LPG), is the major cell surface molecule of promastigotes of all Leishmania species. It is comprised of three domains: a conserved glycosylphosphatidylinositol anchor linked to a repeating phosphorylated disaccharide (P2; PO4-6Gal beta 1-4Man alpha 1-) backbone and capped with a neutral oligosaccharide. In Leishmania major the backbone is substituted at the C(O)3 of the Galp residue with side chains containing Galp, Glcp and Arap residues whereas in Leishmania donovani the backbone is unsubstituted. We report the solubilization of a (beta 1-3) galactosyltransferase [(beta 1-3)GalT] from a L. major microsomal preparation using Triton X-100. Solubilization occurs with a 10-fold stimulation of enzyme activity. This (beta 1-3)GalT specifically transfers Gal residues from UDP-Gal to exogenously added L. donovani LPG acceptor. Depolymerization of the [14C]Gal-labelled LPG product with mild acid and analysis by high-performance anion-exchange chromatography detected only the phosphotrisaccharide. (P3; PO4-6([14C]Gal beta 1-3-4Man alpha 1-) found in L. major LPG. This contrasts with the activity of the membrane-bound enzyme which also synthesizes the larger phosphosaccharide units[Ng, Handman and Bacic (1994) Glycobiology 4, 845-853]. This suggests that more than one (beta 1-3)GalT is involved in the addition of these Gal units and that the solubilized activity is the (beta 1-3)GalT that adds the first beta Gal residue to the acceptor. The (beta 1-3)GalT was partially purified by lectin-affinity chromatography and used to establish the K(m) values for UDP-Gal (445 microM) and L. donovani acceptor (280 microM as P2 molar equivalent) in kinetic assays. Inhibition studies with various glycosides and mono- and di-saccharides established the P2 repeating unit as the minimum acceptor structure recognized by (beta 1-3)GalT. The detergent-solubilized (beta 1-3)GalT was reversibly inactivated by millimolar concentrations of univalent anionic salts. The (beta 1-3)GalT had an absolute requirement for Mn2+ and also required Mg2+ for optimum activity; Mg2+ cannot substitute for Mn2+, which is loosely bound to beta (1-3)GalT and is probably involved in the correct folding of the enzyme. The (beta 1-3)GalT was unaffected by Ca2+ ions, but were irreversibly inactivated by micromolar levels of transition metal ions (Cu2+ > Zn2+ > Ni2 > Co2+). The (beta 1-3)GalT activity was also inhibited by diethyl pyrocarbonate, but not by N-ethylmaleimide or iodoacetamide, suggesting that active-site histidine residues, rather than cysteine residue(s), are important for enzyme activity.

Characterization of lipophosphoglycan from a ricin-resistant mutant of Leishmania major

One of the virulence factors of the protozoan parasite Leishmania major is the surface glycoconjugate, lipophosphoglycan (LPG). A Ricin-resistant mutant of L.major was generated and characterised with respect to its virulence in mice and the structure and expression of LPG. The LPG from this mutant (1F6-B5) retained the tripartite structure of wild-type LPG, comprising a glycosylphosphatidylinositol (GPI) anchor linked to a phosphorylated disaccharide backbone terminating in a nonreducing neutral oligosaccharide cap. The structure of the GPI anchor and the major capping oligosaccharide were identical to wild-type LPG. However, there were variations in the number of phosphorylated repeats (PO4-6Gal(beta 1-4)Man(alpha 1-) comprising the backbone of LPG, although the degree of substitution with side branches (approx. 95%) was similar to that of wild-type LPG. Thus, the mutant LPG was shorter in length having, on average, 15 repeat units per molecule compared with 30 in the wild-type LPG. The mutant LPG contained both arabinose (Ara(beta 1-2)[Gal(beta 1-3)-]1,2) and galactose ([Gal(beta 1-3)-]1-8) capped side branches linked to the backbone. In contrast to wild-type LPG, the number of arabinose-capped side chains was significantly reduced, and a new population of galactose-capped (Gal(beta 1-3)]5-8) side branches was present. The level of LPG expression in mutant parasites was approximately one-tenth of the wild-type parasite. The mutant parasites were avirulent in mice. Over a period of 18 months, they did not cause lesions and organisms could not be isolated from the draining lymph nodes.

Molecular characterization of a stigma-specific gene encoding an arabinogalactan-protein (AGP) from Nicotiana alata

Arabinogalactan-proteins (AGPs) were isolated from the pistils of Nicotiana alata, deglycosylated, and the protein backbones fractionated by reversed-phase HPLC as previously reported. A major fraction, RT35 was isolated and peptide sequences were obtained after protease digestion. A gene-specific degenerate oligonucleotide was designed according to the amino acid sequences and a 380 bp PCR fragment was amplified in vitro from pistil RNA. The PCR fragment was used to screen a pistil cDNA library and a 762 bp cDNA clone (AGPNa3) was isolated and sequenced. The AGPNa3 cDNA encodes a 169 amino acid protein which consists of three domains: an N-terminal secretion signal, a Pro-rich domain and a C-terminal Cys-rich domain. The mature protein has 145 amino acid residues (16.7 kDa) and a predicted pl of 7.5. Northern blot analyses showed that the AGPNa3 gene was only expressed in the pistils of N. alata and of closely related Nicotiana species but not in other plants or suspension-cultured cells. Further Northern blot analysis and in situ hybridization showed that within the pistil, it was primarily expressed in the stigmatic tissues of mature flowers.

Analysis of the structural heterogeneity of laminarin by electrospray-ionisation-mass spectrometry

Electrospray-ionisation-mass spectrometry (ESIMS) was used in conjunction with chemical derivatisation and degradation procedures to analyse the size heterogeneity and branching structure of laminarin from the brown alga, Laminaria digitata. Laminarin is a beta-(1-->3)-linked D-glucan with occasional beta-(1-->6)-linked branches. Electrospray-ionisation-mass spectrometry of permethylated laminarin distinguished two homologous series of molecules, a minor G-series containing 22-28 glucosyl residues, and a more abundant M-series containing 20-30 glucosyl residues linked to a mannitol residue. The relative abundance of all these molecular species could be determined simultaneously from a single mass spectrum, with a mean mass error of 0.6 atomic mass units and a mean mass accuracy of 0.011%. Both series had a mean degree of polymerisation of 25 glucosyl residues, and an approximately 3:1 molar ratio of M-series to G-series molecules was maintained across the range of molecular sizes. Treatment of laminarin with periodate, followed by reduction with borohydride, degraded terminal glucosyl residues on both the main chain and the branches, and allowed the detection of isomers differing solely in their degree of branching. M-series molecules were thus shown to contain 0, 1, 2, 3 or 4 branches, with an average of 1.3 branches per molecule; branched G-series molecules were also detected. Subsequent treatment with acid (Smith degradation) showed that 75% of the branches were single glucosyl residues. This study thus shows how the speed, resolution and mass accuracy of electrospray-ionisation-mass spectrometry can be used in the detailed structural analysis of a polydisperse polysaccharide.

A galactose-rich, cell-wall glycoprotein from styles of Nicotiana alata

A basic, galactose-rich style glycoprotein (GaRSGP) encoded by a previously characterized style-specific cDNA (NaPRP4) has been isolated from the styles of Nicotiana alata and structurally characterized. The glycoprotein is associated with cell walls in the transmitting tract and is composed of approximately 25% (w/w) protein and 75% (w/w) carbohydrate. The purified glycoprotein appears as a smear of between 45-120 kDa on SDS-PAGE; the deglycosylated protein backbone has an apparent molecular weight of approximately 30 kDa. The glycoprotein is rich in the amino acids lysine, proline, and hydroxyproline and in the monosaccharides galactose and arabinose. It is one of only a few proline/hydroxyproline-rich glycoproteins (P/HRGPs) to be characterized both as a cDNA-clone and protein. Glycans are attached to the protein backbone through both O- and N-glycosidic linkages with the majority of the carbohydrate being O-linked and consisting of short, highly branched chains terminating primarily in galactose residues. A carbohydrate epitope(s) is found on both GaRSGP and another style-specific glycoprotein but not on glycoproteins from other tissues. This finding provides further evidence for the existence of a style-specific carbohydrate epitope(s) which may play a role in style function.

Structural analysis of the carbohydrate moiety of arabinogalactan-proteins from stigmas and styles of Nicotiana alata

Arabinogalactan-proteins (AGPs) from the female reproductive tissues (stigmas and styles) of Nicotiana alata were isolated from the saturated ammonium sulfate supernatant of buffer-soluble extracts by precipitation with the beta-glucosyl Yariv reagent, followed by gel-filtration chromatography under dissociating conditions. The AGPs had characteristics typical of other AGPs: a high proportion of carbohydrate (95%) with a high ratio of Gal p to Ara f (2:1), and a low protein content (5%) with high levels of alanine, serine, and hydroxyproline. The AGPs consisted of a major species which was almost neutral, and a minor species which was more negatively charged. Sedimentation equilibrium experiments showed that the purified AGPs had a weight-average molecular weight of 143 kD. Linkage analysis showed that the AGPs contained a highly branched backbone of 3-, 6-, and 3,6-linked Gal p residues, bearing terminal Gal p and terminal Ara f residues. Analysis by one-dimensional and two-dimensional 1H and 13C NMR spectroscopy confirmed the presence of these glycosyl linkage types, and showed a high mobility of the terminal Ara f residues consistent with their location on the periphery of the molecules. This analysis represents the most complete 1H assignment for AGP molecules in solution. No difference in the carbohydrate analyses was found between AGPs isolated separately from stigmatic or stylar tissue, or between AGPs isolated from stigmas and styles of plants of different self-incompatibility genotypes.

Structure of the N-linked oligosaccharides from tridacnin, a lectin found in the haemolymph of the giant clam Hippopus hippopus

Tridacnin, a glycoprotein lectin, was isolated from the symbiotic marine clam Hippopus hippopus and the structure of its major N-glycan chains determined. Tridacnin contains only N-linked glycans which were quantitatively cleaved by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. Following purification by anion-exchange HPLC, the structures of the oligosaccharides were established using a combination of electrospray ionisation mass spectrometry, 1H-NMR spectroscopy and linkage analysis. The N-glycans are primarily of the oligomannose type but, in addition, some contain a novel 6-O-Me group on the terminal mannose residue of the chain. The N-glycan chains had the following structures. [formula: see text]

Molecular cloning of cDNAs encoding the protein backbones of arabinogalactan-proteins from the filtrate of suspension-cultured cells of Pyrus communis and Nicotiana alata

This paper reports the isolation of cDNAs encoding the protein backbone of two arabinogalactan-proteins (AGPs), one from pear cell suspension cultures (AGPPc2) and the other from suspension cultures of Nicotiana alata (AGPNa2). The proteins encoded by these cDNAs are quite different from the 'classical' AGP backbones described previously for AGPs isolated from pear suspension cultures and extracts of N. alata styles. The cDNA for AGPPc2 encodes a 294 amino acid protein, of which a relatively short stretch (35 amino acids) is Hyp/Pro rich; this stretch is flanked by sequences which are dominated by Asn residues. Asn residues are not a feature of the 'classical' AGP backbones in which Hyp/Pro, Ser, Ala and Thr account for most of the amino acids. The cDNA for AGPNa2 encodes a 437 amino acid protein, which contains two distinct domains: one rich in Hyp/Pro, Ser, Ala, Thr and the other rich in Asn, Tyr and Ser. The composition and sequence of the Pro-rich domain resembles that of the 'classical' AGP backbone. The Asn-rich domains of the two cDNAs described have no sequence similarity; in both cases they are predicted to be processed to give a mature backbone with a composition similar to that of the 'classical' AGPs. The study shows that different AGPs can differ in the amino acid sequence in the protein backbone, as well as the composition and sequence of the arabinogalactan side-chains. It also shows that differential expression of genes encoding AGP protein backbones, as well as differential glycosylation, can contribute to the tissue specificity of AGPs.

Microheterogeneity of N-glycosylation on a stylar self-incompatibility glycoprotein of Nicotiana alata

Gametophytic self-incompatibility, a mechanism that prevents inbreeding in some families of flowering plants, is mediated by the products of a single genetic locus, the S-locus. The products of the S-gene in the female sexual tissues of Nicotiana alata are an allelic series of glycoproteins with RNase activity. In this study, we report on the microheterogeneity of N-linked glycosylation at the four potential N-glycosylation sites of the S2-glycoprotein. The S-glycoproteins from N.alata contain from one to five potential N-glycosylation sites based on the consensus sequence Asn-Xaa-Ser/Thr. The S2-glycoprotein contains four potential N-glycosylation sites at Asn27, Asn37, Asn38 and Asn 150, designated sites I, II, IV and V, respectively. Site III is absent from the S2-glycoprotein. Analysis of glycopeptides generated from the S2-glycoprotein by trypsin and chymotrypsin digestions revealed the types of glycans and the degree of microheterogeneity present at each site. Sites I (Asn27) and IV (Asn138) display microheterogeneity, site II (Asn37) contains only a single type of N-glycan, and site V (Asn150) is not glycosylated. The microheterogeneity observed at site I on the S2-glycoprotein is the same as that observed at the only site, site I, on the S1-glycoprotein (Woodward et al., Glycobiology, 2, 241-250, 1992). Since the N-glycosylation consensus sequence at site I is conserved in all S-glycoproteins from other species of self-incompatible solanaceous plants, glycosylation at this site may be important to their function. No other post-translational modifications (e.g. O-glycosylation, phosphorylation) were detected on the S2-glycoprotein.

Lipophosphoglycan blocks attachment of Leishmania major amastigotes to macrophages

Promastigotes of the intracellular protozoan parasite Leishmania major invade mononuclear phagocytes by a direct interaction between the cell surface lipophosphoglycan found on all Leishmania species and macrophage receptors. This interaction is mediated by phosphoglycan repeats containing oligomers of beta (1-3)Gal residues specific to L. major. We show here that although amastigotes also use lipophosphoglycan to bind to both primary macrophages and a cell line, this interaction is independent of the beta (1-3)Gal residues employed by promastigotes. Binding of amastigotes to macrophages could be blocked by intact lipophosphoglycan from L. major amastigotes as well as by lipophosphoglycan from promastigotes of several other Leishmania species, suggesting involvement of a conserved domain. Binding of amastigotes to macrophages could be blocked significantly by the monoclonal antibody WIC 108.3, directed to the lipophosphoglycan backbone. The glycan core of lipophosphoglycan could also inhibit attachment of amastigotes, but to a considerably lesser extent. The glycan core structure is also present in the type 2 glycoinositolphospholipids which are expressed on the surface of amastigotes at 100-fold-higher levels than lipophosphoglycan. However, their inhibitory effect could not be increased even when they were used at a 300-fold-higher concentration than lipophosphoglycan, indicating that lipophosphoglycan is the major macrophage-binding molecule on amastigotes of L. major. In the presence of complement, the attachment of amastigotes to macrophages was not altered, suggesting that lipophosphoglycan interacts directly with macrophage receptors.

Biosynthesis of lipophosphoglycan from Leishmania major: characterization of (beta 1-3)-galactosyltransferase(s)

Lipophosphoglycan (LPG) is the major cell surface molecule of promastigotes of all Leishmania species. It is comprised of three domains: a conserved GPI anchor linked to a repeating phosphorylated disaccharide (P2; PO4-6-Gal(beta 1-4)Man(alpha 1-) backbone variously substituted with galactose, glucose and arabinose residues in L.major and capped with a neutral oligosaccharide. Using a microsomal membrane preparation from L.major, we have been able to demonstrate that galactose from UDP-[14C]galactose can be transferred to an endogenous acceptor, characterized as LPG. An in vitro assay was established, based on anion-exchange HPLC, that concurrently identifies and quantitates the products of the galactosyltransferases. We show that the products formed are [14C]galactose-labelled P3 (PO4-6-[Gal(beta 1-3)]Gal(beta 1-4)Man(alpha 1-), P4b (PO4-6-[Gal(beta 1-3)Gal(beta 1-3)]Gal(beta 1-4)Man(alpha 1-) and P5b(PO4-6-[Gal(beta 1-3)Gal(beta 1-3)Gal(beta 1-3)]Gal(beta 1- 4)Man(alpha 1-). These are major galactosylated repeating units of the backbone of L.major LPG. The same products are also formed when LPG from L.donovani, which contains an unbranched backbone of P2 repeats, is used as an exogenous acceptor with L.major microsomal membranes and UDP-[14C]galactose. In addition, no formation of radioactive backbone repeats (P2) was detected in membrane incubations containing UDP-[14C]galactose with or without added unlabelled GDP-mannose, indicating that the addition of the (beta 1-3)-linked galactose branches is independent of the synthesis of the repeating disaccharide (P2) backbone. Preliminary kinetic analyses suggest that the addition of multiple (beta 1-3)-linked galactose residues may be catalysed by more than one (beta 1-3) galactosyltransferase. The (beta 1-3)galactosyltransferase(s) activity was not detected in microsomal membrane preparations from promastigotes of L.donovani.

Isolation of the protein backbone of an arabinogalactan-protein from the styles of Nicotiana alata and characterization of a corresponding cDNA

Arabinogalactan-proteins (AGPs) from the styles of Nicotiana alata were isolated by ion exchange and gel filtration chromatography. After deglycosylation by anhydrous hydrogen fluoride, the protein backbones were fractionated by reversed-phase HPLC. One of the protein backbones, containing mainly hydroxyproline, alanine, and serine residues (53% of total residues), was digested with proteases, and the peptides were isolated and sequenced. This sequence information allowed the cloning of a 712-bp cDNA, AGPNa1. AGPNa1 encodes a 132-amino acid protein with three domains: an N-terminal secretion signal sequence, which is cleaved from the mature protein; a central sequence, which contains most of the hydroxyproline/proline residues; and a C-terminal hydrophobic region. AGPNa1 is expressed in many tissues of N. alata and related species. The arrangement of domains and amino acid composition of the AGP encoded by AGPNa1 are similar to that of an AGP from pear cell suspension culture filtrate, although the only sequence identity is at the N termini of the mature proteins.

Molecular cloning of a gene encoding an arabinogalactan-protein from pear (Pyrus communis) cell suspension culture

Arabinogalactan-proteins (AGPs) are proteoglycans containing a high proportion of carbohydrate (typically > 90%) linked to a protein backbone rich in hydroxyproline (Hyp), Ala, Ser, and Thr. They are widely distributed in plants and may play a role in development. The structure of the carbohydrate of some AGPs is known in detail but information regarding the protein backbone is restricted to a few peptide sequences. Here we report isolation and partial amino acid sequencing of the protein backbone of an AGP. This AGP is a member of one of four major groups of AGPs isolated from the filtrate of pear cell suspension culture. A cDNA encoding this protein backbone (145 amino acids) was cloned; the deduced protein is rich in Hyp, Ala, Ser, and Thr, which together account for > 75% of total residues. It has three domains, an N-terminal secretion signal, a central hydrophilic domain containing all of the Pro residues, and a hydrophobic C-terminal domain that is predicted to be a transmembrane helix. Approximately 93% of the Pro residues are hydroxylated and hence are potential sites for glycosylation.

A style-specific hydroxyproline-rich glycoprotein with properties of both extensins and arabinogalactan proteins

A basic, hydroxyproline-rich glycoprotein (molecular mass 120 kDa) has been purified from the styles of Nicotiana alata. An antibody, specific for the protein backbone (molecular mass 78 kDa) of the glycoprotein, was used to demonstrate that the glycoprotein is a soluble, style-specific component and that related molecules are present in the styles of other solanaceous species. Linkage analysis of the carbohydrate portion of the glycoprotein, together with antibody binding studies, indicates that the glycoprotein contains both extensin-like and arabinogalactan-protein (AGP)-like side chains. Furthermore, the AGP-like side-chains contain a style-specific epitope that is also present on AGPs from N. alata styles and glycoconjugates from the styles of other members of the Solanaceae. The abundance of this 120 kDa glycoprotein, its location in the extracellular matrix of the transmitting tract and its conservation in several species within the Solanaceae suggests a role in pistil function.

Epitope mapping of monoclonal antibodies directed against lipophosphoglycan of Leishmania major promastigotes

Monoclonal antibodies (MAbs) were generated against Leishmania major promastigote lipophosphoglycan (LPG) to use as tools in defining functional epitopes of this major cell surface glycoconjugate. Epitope mapping of four MAbs, designated 4A2-A2, 2G11-A3, 5E6-D10 and 5E10-F2, revealed that the phosphorylated oligosaccharide repeat unit PO4-6[Gal(beta 1-3)]Gal(beta 1-4)Man alpha 1-, P3, is a highly immunogenic epitope which has previously been demonstrated, by chemical analyses, to be a repeat unit specific to L. major. Two antibodies, 4A2-A2 and 5E10-F2, also recognised the repeat unit PO4-6[Ara(beta 1-2)Gal(beta 1-3)]Gal(beta 1-4)Man alpha 1-, 4Pa, with less affinity than P3, while 2G11-A3 recognised P4a with greater affinity than for P3. The L. major metacyclic-specific antibody 3F12 only recognised repeat units terminating with arabinose residues. In particular, 3F12 recognised P4a, which is upregulated in metacyclic LPG compared to the procyclic form of the molecule. The oligosaccharides P3, P4a and P5a are specific to L. major LPG. The epitopes of 4A2-A2, 2G11-A3, 5E6-D10 and 5E10-F2 were found on the cell surface and in the flagellar pocket of both procyclic and metacyclic V121 promastigotes, but were only detected at very low levels on amastigotes. The repeat unit P3 is able to inhibit attachment of procyclic promastigotes to the midgut of the sandfly vector, but neither Fab fragments of the four antibodies nor purified P3 could inhibit attachment of metacyclic promastigotes to the macrophage cell line J774. It was also shown that human sera from patients with cutaneous leishmaniasis recognised purified P3. The data suggests that while P3 is an immunogen in the natural course of infection of the human host, P3 plays no role in attachment and internalisation of promastigotes into the macrophages of the mammalian host.