Structural elucidation and monokine-inducing activity of two biologically active zwitterionic glycosphingolipids derived from the porcine parasitic nematode Ascaris suum

The isolated neutral glycosphingolipid fraction from the pig parasitic nematode, Ascaris suum, was fractionated by silica gel chromatography to yield a neutral and a zwitterionic glycosphingolipid fraction, the latter of which mainly contained two zwitterionic glycosphingolipids termed components A and C. Preliminary chemical characterization with hydrofluoric acid treatment and immunochemical characterization with a phosphocholine-specific monoclonal antibody indicated that both components contained phosphodiester substitutions: phosphocholine for component A, and phosphocholine and phosphoethanolamine for component C. Both components were biologically active in inducing human peripheral blood mononuclear cells to release the inflammatory monokines tumor necrosis factor alpha, interleukin 1, and interleukin 6. Component A was the more bioactive molecule, and its biological activity was abolished on removal of the phosphocholine substituent by hydrofluoric acid. The glycosphingolipid components were structurally analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, liquid secondary ion mass spectrometry, methylation analysis, 1H NMR spectroscopy, exoglycosidase cleavage, and ceramide analysis. Their chemical structures were elucidated to be (see Structure I below), [structure: see text] The carbohydrate moiety oligosaccharide core was characterized as belonging to the arthro series of protostomial glycosphingolipids. The ceramide moiety was distinguished by (R)-2-hydroxytetracosanoic acid as the dominant fatty acid species and by the C17 iso-branched sphingosine and sphinganine bases, 15-methylhexadecasphing-4-enine and 15-methylhexadecasphinganine, respectively.

Structural analysis of neutral glycosphingolipids from Ascaris suum adults (Nematoda:Ascaridida)

The neutral glycosphingolipid fraction from adults of the pig parasitic nematode, Ascaris suum, was resolved into four components on thin-layer chromatography. The high-performance liquid chromatography-isolated components were structurally analysed by: methylation analysis; exoglycosidase cleavage; gas-liquid chromatography/mass spectrometry; liquid secondary-ion mass spectrometry; and, in particular, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Their chemical structures were determined as: Glc(beta 1-1)ceramide, Man(beta 1-4)Glc(beta 1-1)ceramide, GlcNAc(beta 1-3)Man(beta 1-4)Glc(beta 1-1)ceramide and Gal(alpha 1-3)GalNAc(beta 1-4)GlcNAc(beta 1-3)Man(beta 1-4)Glc(beta 1-1)ceramide; and were characterized as belonging to the arthro-series of protostomial glycosphingolipids. No glycosphingolipid component corresponding to ceramide tetrasaccharide was detected during these analyses. The ceramide composition of the parent glycosphingolipids was dominated by the 2-(R)-hydroxy C24:0 fatty acid, cerebronic acid, and C17 sphingoid-bases: 15-methylhexadecasphing-4-enine and 15-methylhexadecaphinganine in approximately equal proportions. The component ceramide monohexoside was characterized by an additional 15-methylhexadecaphytosphingosine.

Isolation and structural analysis of three neutral glycosphingolipids from a mixed population of Caenorhabditis elegans (Nematoda:Rhabditida)

The free-living nematode, Caenorhabditis elegans, has been proposed and analyzed as a prototypic model for parasitic nematodes. In order to study whether there is a structural basis for the proposed analogy with respect to nematode glycoconjugates, we have analyzed Caenorhabditis elegans glycosphingolipids. Three, simple neutral glycosphingolipid components of the neutral glycolipid fraction were isolated by high-performance liquid chromatography. Structural analysis was performed by methylation analysis, exoglycosidase cleavage, matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry, and ceramide analysis. The chemical structures have been determined as Glc beta 1Cer, Man beta 4Glc beta 1Cer and GlcNAc beta 3Man beta 4Glc beta 1Cer; that are characterized as belonging to the arthroseries of protostomial glycosphingolipids. The ceramide moiety of the parent glycosphingolipid-ceramide mono-hexoside was dominated by 2-hydroxy fatty acids, and a d17:1 spingoid-base with an iso- or anteiso-branched chain. The chemical composition of the three glycosphingolipids from Caenorhabditis elegans displayed close structural coincidence with the equivalent structures from the porcine parasitic nematode, Ascaris suum (G.Lochnit, R.D. Dennis, U.Zähringer, and R.Geyer, Glycoconjugate J., 1997), in support of this organism as a prototypic glycosphingolipid model for parasitic nematodes.

Isolation and partial characterization of a fatty-acid-binding protein from Ascaris suum reproductive tissue

A 12-kDa fatty-acid-binding protein was purified to homogeneity from Ascaris suum reproductive tissue as confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. N-terminal amino-acid-sequence analysis of the protein revealed its identity with the ABA-1 allergen protein isolated from A. suum pseudocoelomic fluid. Fatty-acid binding by the protein from A. suum reproductive tissue was investigated using the Lipidex 1000 assay, which revealed the presence of a single class of fatty-acid-binding sites with an apparent dissociation constant for palmitate of about 0.8 microM.

Lophotoxin-insensitive nematode nicotinic acetylcholine receptors

Nematode nicotinic acetylcholine receptors (nAChRs) are molecular targets of several anthelmintic drugs. Studies to date on Caenorhabditis elegans and Ascaris suum have demonstrated atypical pharmacology with respect to nAChR antagonists, including the finding that kappa-bungarotoxin is a more effective antagonist than alpha-bungarotoxin on Ascaris muscle nAChRs. Lophotoxin and its naturally occurring analogue bipinnatin B block all vertebrate and invertebrate nAChRs so far examined. In the present study, the effects on nematode nAChRs of bipinnatin B have been examined. The Ascaris suum muscle cell nAChR was found to be insensitive to 30 mumol l-1 bipinnatin B, a concentration that is highly effective on other nAChRs. To our knowledge, this is the first demonstration of a nAChR that is insensitive to one of the lophotoxins. Xenopus laevis oocytes injected with C. elegans polyadenylated, poly(A+), mRNA also expressed bipinnatin-B-insensitive levamisole responses, which were, however, blocked by the nAChR antagonist mecamylamine (10 mumol l-1). In contrast to the findings for nematode receptors, bipinnatin B (30 mumol l-1) was effective in blocking mouse muscle nAChRs expressed in Xenopus laevis oocytes and native insect nAChRs. A possible explanation for insensitivity of certain nematode nAChRs to lophotoxins is advanced based on the sequence of an alpha-like C. elegans nAChR subunit in which tyrosine-190 (numbering based on the Torpedo californica sequence), a residue known to be critical for lophotoxin binding in vertebrate nAChRs, is replaced by a proline residue.

Structure of the ascarosides from Ascaris suum

Six glycosides have been identified from the nematode Ascaris suum. The glycon part of all six glycosides is alpha L-3,6-dideoxymannose, previously known as ascarylose. The major components (4 and 5) and the minor components (8 and 9) have been shown by NMR and electrospray MS to involve a mixture of two homologous aglycons: the 2, omega-1 diols of hentriacontane and tritriacontane. Compounds 4 and 5 are glycosylated on only one of the hydroxy groups, while 8 and 9 are glycosylated on both. These compounds resemble ascarosides B and C previously isolated from Parascaris equorum. However, these aglycons are reported to be based on the 2,6-diol of hentriacontane. Compounds 6 and 7 are based on 2-hydroxy-nonacosane and 2-hydroxy-28-methylnonacosane glycosylated at C-2 with the same sugar. Although 6 and 7 are related to ascaroside A, previously isolated from P. equorum, these earlier reports suggest the chain in ascaroside A to be unbranched.

Repetitive peptide motifs in the cuticlin of Ascaris suum

The cuticle of parasitic nematodes is composed of extracellular structural proteins. Over 90% of these proteins are collagenous molecules in the basal and median layers of the cuticle. The outermost layers of the cuticle, the epicuticle, is composed of non-collagenous proteins, that represent the structural surface of nematodes. In Ascaris these proteins have been termed 'cuticlins'. While cuticular collagens have been well studied by both biochemical and genetic means, knowledge of the molecular structure of cuticlin components of parasitic nematodes is scarce. In the present paper we report on the production of monoclonal antibody 8.1, which is specific for cuticlin, but does not recognize collagen epitopes. We have screened a cDNA library derived from adult Ascaris suum mRNA of the hypodermal tissue underlying and synthesizing the cuticle. One positive cDNA clone encodes alanine-rich repetitive motifs, which are part of the insoluble cuticlin of the outermost layers of the epicuticle of Ascaris suum. This was shown in immunocytochemical experiments using specific polyclonal antisera raised against these motifs, expressed as fusion protein with glutathione S-transferase of the helminth Schistosoma japonicum. Comparison of the repetitive amino acid sequence with structural proteins of the nematode Caenorhabditis elegans and the insects Locusta migratoria and Ceratitis capitata revealed a minimal consensus motif.

Structural characterization of a novel glycoinositolphospholipid from the parasitic nematode, Ascaris suum

A novel glycosphingolipid containing inositol phosphate as an acidic group has been demonstrated in whole tissues of the porcine roundworm, Ascaris suum. The thin layer chromatographic pattern of the total acidic glycolipid revealed the presence of several components, of which a major component (named AGL) with positive reactions toward both orcinol-sulfuric acid (sugar) and molybdate (phosphate) spray reagents was isolated and purified by the use of successive column chromatography on DEAE-Sephadex and silicic acid (latrobeads). From structural studies including compositional sugar analysis, hydrogen fluoride degradation, methylation analysis, periodate oxidation, proton magnetic resonance spectroscopy and fast atom bombardment mass spectrometry, the structure of AGL was deduced to be Gal alpha 1-2Ins(1-->)-P-Cer. Aliphatic constituents were lignoceric acid and its 2-hydroxy homologue as the principal fatty acids, and octadecasphinganine and branched heptadecasphinganine as the major sphingoids.

Effects of pH on a high conductance Ca-dependent chloride channel: a patch-clamp study in Ascaris suum

Plasma membrane vesicles prepared from the bag region of the somatic muscle cells of the parasitic nematode Ascaris suum contain high conductance, voltage sensitive, Ca-dependent chloride channels, suggested to be involved in the excretion of carboxylic acids produced by the anaerobic respiration of glucose (Valkanov, Martin & Dixon, 1994). The effect of altered pH on this channel was investigated using the patch-clamp technique and isolated inside-out membrane patches. Changes in pH had little effect on channel conductances and only a small effect on reversal potentials. Under control conditions (symmetrical pH 7.2) the channel had the highest probability of opening at approximately -35 mV (the resting membrane potential of the cell). At positive membrane potentials the probability of opening decreased. The Boltzmann equation was used to describe the relationship between membrane potential and probability of channel opening, and to calculate the effective gating charge. Reduction of external pH produced an increase in the probability of channel opening at hyperpolarized membrane potentials. An increase in internal pH caused a voltage-independent increase in the probability of channel opening and made the effective gating charge less negative. The effect of reducing internal pH was marked: the channel then opened most frequently at positive membrane potentials and the probability of opening at -35 mV was greatly reduced. The decrease in internal pH changed the polarity of the effective gating charge. A simple model was constructed to describe the effects of pH on channel gating.

The motile major sperm protein (MSP) from Ascaris suum is a symmetric dimer in solution

The major sperm protein (MSP) of Ascaris suum mediates amoeboid motility by forming an extensive intermeshed system of cytoskeletal filaments analogous to that formed by actin in many amoeboid cells. We have used a combination of biochemical and NMR methods to show that, in contrast to actin, MSP exist in solution as a symmetrical dimer. This result has important implications for the mechanism of both MSP filament assembly and the recognition of different MSP isoforms in vivo.

Molecular and functional properties of cytochrome c from adult Ascaris suum muscle

Mitochondrial cytochrome c was isolated at high purity from adult Ascaris suum muscle and its molecular properties were investigated. The molecular weight of A. suum cytochrome c was determined to be 13,119 by electrospray ionization mass spectrometry. The oxidation-reduction potential of nematode cytochrome c was measured to be +248 mV; this value is comparable to those for cytochrome c from mammalian sources. The A. suum cytochrome c, like bovine heart cytochrome c, showed biphasic kinetics against bovine heart cytochrome c oxidase. Comparative kinetic studies revealed species-specificity in the reaction between cytochrome c and cytochrome c oxidase from A. suum and bovine sources. The cytochrome c content in mitochondria was highest at the second larval stage, in which the respiratory chain is the most aerobic among various developmental stages of A. suum. These data clearly show that adult A. suum cytochrome c, as isolated, is a bona fide substrate for cytochrome c oxidase in the aerobic respiratory chain of second-stage larvae.

Neuronal localization of serotonin in the nematode Ascaris suum

We have used immunocytochemical techniques to investigate the distribution of serotonin-like immunoreactivity in the nematode Ascaris suum. Antisera raised against serotonin (5-hydroxytryptamine, 5-HT) conjugated to bovine serum albumin (BSA) labelled a pair of neurons in the pharynx of both sexes and five cells in the ventral cord of the male tail. The labelling was blocked by 5-HT or by 5-HT conjugated to BSA. The 5-HT-immunoreactive cells in the pharynx resemble neurosecretory cells and are probably homologous to the neurosecretory motor neurons (NSM) in Caenorhabditis elegans; the cells in the male tail appear to be motor neurons that are homologous to CP neurons in C. elegans. Other cells that stain with 5-HT antisera have been observed in C. elegans but are not seen in Ascaris.

Purification and molecular characterization of a novel b5-type cytochrome of the parasitic nematode, Ascaris suum

A b5-type cytochrome was extracted from Ascaris suum muscle at pH 4.5 with 0.3% aluminum sulfate and purified by ammonium sulfate fractionation, ion-exchange chromatography on CM-500 Cellulofine, and gel filtration on Sephadex G-75. The hemoprotein displayed a typical absorption spectrum of cytochrome b with a midpoint redox potential of 78 mV. The N-terminal amino acid sequence was determined and revealed the N-terminus to be highly homologous to the heme-binding domain of vertebrate cytochrome b5. Using an oligonucleotide probe synthesized based on the amino acid sequence of the purified protein, the cDNA clone encoding A. suum cytochrome b5 was isolated from the lambda ZAP II cDNA library. The entire nucleotide sequence of 563 bases comprised an open reading frame of 339 bases encoding a precursor protein of 112 amino acid residues. The purified cytochrome B5 was predicted to contain 82 amino acids with a molecular mass of 9141 Da, matching the 9140 Da obtained from electrospray ionization mass spectometry, and to lack of membrane-anchor domain at the C-terminus. In contrast, an N-terminal extension of 30 amino acids, characteristic of signal peptides, was apparent. Immunoblots revealed the presence of an A. suum cytochrome b5 of 82 amino acids, but no protein with an N-terminal extension. These results demonstrate a novel cytochrome b5 possessing a presequence.

Characterization of subtypes of gamma-aminobutyric acid receptors in an Ascaris muscle preparation by binding assay and binding of PF1022A, a new anthelmintic, on the receptors

We examined the effect of PF1022A, one of the gabergic anthelmintics newly developed in Japan, on gamma-aminobutyric acid (GABA) receptors using a radioligand binding technique in isolated membrane preparations of the nematode Ascaris suum. Membrane protein was prepared from the homogenate of somatic muscle cells after ultracentrifugation. In addition to the basic binding of [2,3-3H-(N)]-GABA, the radioligand [methyl-3H]-bicuculline is used to identify the GABAA receptor, whereas [butyl-4-3H]-baclofen is employed for GABAB receptor sites. The dissociation constants (Kd values) and the maximal numbers of binding sites (Bmax values) from Scatchard plotting for GABA receptors are close to those obtained in mammalian brain. PF1022A displaced in a concentration-dependent way the binding of [2,3-3H(N)]-GABA and [methyl-3H]-bicuculline as did other specific gabergic agents. In addition, PF1022A decreased the binding of [butyl-4-3H]-baclofen at a higher concentration, although this binding did not represent GABAB sites. In a comparison of the inhibition constants (Ki values) of PF1022A with those of other agents, it is conclusive that PF1022A bound with GABA receptors. A direct effect of PF1022A on GABA receptors can thus be postulated.

Glycerophosphorylcholine, a component of both Ascaris suum muscle and Caenorhabditis elegans

Studies of the muscle phospholipid metabolism of Ascaris suum suggest an effect of cholinergic drugs on the turnover of phosphatidylcholine and the generation of glycerophosphorylcholine (GPC). 31P-nuclear magnetic resonance (NMR) studies of helminths revealed the presence of a major peak that was assigned to GPC. The primary effect of the cholinergic drugs on the parasites' phosphate profile appeared to be on the level of GPC. In in vivo studies, decreases in internal GPC concentrations occurred prior to any decrease in the concentration of ATP. The importance of these studies relies on the correct identity of this major 31P-NMR resonance. More recently, the identity of this resonance as GPC was questioned by experimental data obtained from C. elegans dauer larvae using the NMR technique. Because studies from our laboratory suggested that phospholipid metabolism may be intimately connected with the parasite's responses to drugs, the identity of the assigned resonance in the 31P-NMR spectrum as GPC in Ascaris suum was reexamined and found to be correct. Similar studies with C. elegans indicate the presence of both GPC and GPE.

Initiation of chemical studies on the immunoreactive glycolipids of adult Ascaris suum

There is a general lack of basic information concerning one class of glycoconjugate, the glycolipids, from parasitic nematodes. As the prototype, the neutral glycolipid fraction derived from adult males of Ascaris suum was investigated as to its chromatographic, differential chemical staining, antigenic and chemical properties. The thin-layer chromatography-resolved neutral fraction glycolipids could be classified into components of fast and slow migrating band groups. Immunoreactivity was restricted to the latter as detected by IgG and IgM anti-neutral fraction glycolipid antibody levels in serial infection sera of mice. Similarities of chromatography, antigenicity and serological cross-reactivity have been extended to the neutral glycolipid fractions of other parasitic nematodes: Litomosoides carinii and Nippostrongylus brasiliensis. Chemical, differential chemical staining and enzymatic analyses identified the Ascaris suum antigenic, slow migrating band group of components as amphoteric glycosphingolipids, and not the originally hypothesized glycoglycerolipids or glycosylphosphatidylinositols, that contained typical neutral monosaccharide constituents and a zwitterionic phosphodiester linkage, most probably phosphocholine. Glycosphingolipid-immunoreactivity is eliminated on cleavage of the zwitterionic phosphodiester linkage by hydrofluoric acid treatment.

IgE regulation by nematodes: the body fluid of Ascaris contains a B-cell mitogen

Nematode infection of human beings or laboratory animals leads to markedly increased levels of circulating IgE, most of which is not specific to worm antigens. This phenomenon is known to be interleukin-4-dependent, but little is known about the mechanism of activation of the response. In an attempt to elucidate this mechanism, we have used a reductive approach with worm products rather than infections. In a previous article we showed that injection of the body fluid of the nematode Ascaris yields a marked increase in circulating IgE. In this study we demonstrate that the body fluid contains a B-cell mitogen. Incubation with purified splenic B cells with 50 micrograms/ml body fluid yields marked proliferation of B cells, as measured by tritiated thymidine uptake. Similarly, Ascaris body fluid stimulates G0 B cells to enter the cell cycle. T cells are unaffected by the mitogen, and the response is dependent on viable accessory cells. Contamination of Ascaris body fluid or reagents by bacterial lipopolysaccharide has been ruled out as a source of artefactual data. A model is proposed, which suggests that the B-cell mitogen in Ascaris body fluid stimulates polyclonal B-cell activity and that other nematode factors either stimulate the release of interleukin-4 or act in an interleukin-4-like manner to cause class switch to IgE.

The ABA-1 allergen of the parasitic nematode Ascaris suum: fatty acid and retinoid binding function and structural characterization

We report here on the structure and function of the ABA-1 allergen protein of the parasitic nematode Ascaris, the first nematode allergen to be characterized in detail. Using the fluorescent fatty acid analog 11-(((5-(dimethylamino)-1-naphthalenyl)sulfonyl)amino)undecanoic acid (DAUDA), it was demonstrated that ABA-1 is a fatty acid binding protein (FABP) with a high affinity for the fluorescent analog (8.8 x 10(-8) M) and for oleic acid in competition experiments (1.3 x 10(-8) M), with a single binding site for ligand per monomer unit. Blue-shifting of fluorescence emission of DAUDA upon binding was unprecedented in degree among FABPs, being equivalent to that occurring in cyclohexane. A similarly blue-shifted spectrum was obtained with a probe in which the fluorophore was bound to the alpha carbon of a fatty acid, indicating that the carboxylate group of bound fatty acids is probably not exposed to solvent. In competition experiments and by observation of changes in their intrinsic fluorescence, retinol and retinoic acid were also found to bind in the fatty acid binding site. Circular dichroism (CD) of the ABA-1 protein revealed a high alpha-helix content (59%) which was consistent with the four-helix structure for the protein predicted from sequence algorithms. Fluorescence measurements showed that the single, highly conserved tryptophan residue is deeply buried in an unusually apolar environment and that this was unaffected by ligand binding. DSC studies of thermal stability indicate that unfolding of the ABA-1 dimer is cooperative and biphasic (Tm approximately 71 and 89 degrees C), suggesting a two-domain thermal unfolding process, again consistent with the predicted structure. Only the folding of the high-temperature domain is reversible on cooling. DSC confirmed the gel filtration analysis, which indicated that ABA-1 forms a dimer. Aside from being the first nematode allergen for which structure or function has been elucidated, ABA-1 provides a highly manipulable model for investigation of the interaction between hydrophobic ligands and alpha-helical proteins.

Eight novel FMRFamide-like neuropeptides isolated from the nematode Ascaris suum

Eight FMRFamide-like neuropeptides were isolated from an extract of heads and tails from the nematode Ascaris suum using seven steps of HPLC. The peptides ranged in size from 8 to 14 amino acid residues: AF3 (Ala-Val-Pro-Gly-Val-Leu-Arg-Phe-amide), AF4 (Gly-Asp-Val-Pro-Gly-Val-Leu-Arg-Phe-amide), AF5 (Ser-Gly-Lys-Pro-Thr-Phe-Ile-Arg-Phe-amide), AF7 (Ala-Gly-Pro-Arg-Phe-Ile-Arg-Phe-amide), AF9 (Gly-Leu-Gly-Pro-Arg-Pro-Leu-Arg-Phe-amide), AF10 (Gly-Phe-Gly-Asp-Glu-Met-Ser-Met-Pro-Gly-Val-Leu-Arg-Phe-amide), AF11 (Ser-Asp-Ile-Gly-Ile-Ser-Glu-Pro-Asn-Phe-Leu-Arg-Phe-amide), and AF12 (Phe-Gly-Asp-Glu-Met-Ser-Met-Pro-Gly-Val-Leu-Arg-Phe-amide). The effect of synthetic AF4 on muscle tension in a dorsal muscle strip preparation was a strong, long-lasting contraction. PF1, a peptide present in Panagrellus redivivus and Caenorhabditis elegans, relaxed the AF4-induced contraction.

The motile major sperm protein (MSP) of Ascaris suum forms filaments constructed from two helical subfilaments

The amoeboid motility nematode sperm is mediated by cytoskeletal filaments composed of major sperm protein (MSP). We have used electron microscopy and image processing to show that MSP filaments are constructed from two subfilament strands which are themselves formed from a helical arrangement of subunits. The subfilaments are based on left-handed helices of pitch 9 nm that then coil along right-handed helical tracks of pitch 22.5 nm to form filaments. The subfilaments appear to be indistinguishable from the helices present in orthorhombic crystals of MSP. Because in filaments the subfilaments are themselves helical, not all subunits are able to participate in protein-protein interactions between different strands. One consequence of this interaction geometry is that the same molecular interactions that function to assemble subfilaments into filaments can also be used to assemble filaments into larger supramolecular assemblies such as the macrofibres formed in vitro and the fibre bundles found in vivo in sperm pseudopods. These results indicate the importance of filament bundling in addition to vectorial filament assembly in amoeboid cell motility.

Supramolecular assemblies of the Ascaris suum major sperm protein (MSP) associated with amoeboid cell motility

Sperm of the nematode, Ascaris suum, are amoeboid cells that do not require actin or myosin to crawl over solid substrata. In these cells, the role usually played by actin has been taken over by major sperm protein (MSP), which assembles into filaments that pack the sperm pseudopod. These MSP filaments are organized into multi-filament arrays called fiber complexes that flow centripetally from the leading edge of the pseudopod to the cell body in a pattern that is intimately associated with motility. We have characterized structurally a hierarchy of helical assemblies formed by MSP. The basic unit of the MSP cytoskeleton is a filament formed by two subfilaments coiled around one another along right-handed helical tracks. In vitro, higher-order assemblies (macrofibers) are formed by MSP filaments that coil around one another in a left-handed helical sense. The multi-filament assemblies formed by MSP in vitro are strikingly similar to the fiber complexes that characterize the sperm cytoskeleton. Thus, self-association is an intrinsic property of MSP filaments that distinguishes these fibers from actin filaments. The results obtained with MSP help clarify the roles of different aspects of the actin cytoskeleton in the generation of locomotion and, in particular, emphasize the contributions made by vectorial assembly and filament bundling.

The molecular structure of the complex of Ascaris chymotrypsin/elastase inhibitor with porcine elastase

BACKGROUND

The intestinal parasitic worm, Ascaris suum, produces a variety of protein inhibitors that defend the organism against the host's proteinases. Eight different proteins from Ascaris suum have been identified as inhibitors of serine proteinases, targeting chymotrypsin, elastase and trypsin. These inhibitors share 30-40% sequence identity with one another, but have virtually no sequence identity with members of any of the other families of serine proteinase inhibitors.

RESULTS

The crystal structure of the complex of porcine pancreatic elastase with a chymotrypsin/elastase inhibitor from Ascaris suum (the C/E-1 inhibitor) has been solved to 2.4 A resolution by the molecular replacement method. The C/E-1 inhibitor exhibits a novel folding motif. There are only two small beta-sheets and two single-turn 3(10)-helices in this inhibitor. Unlike the majority of proteins, the C/E-1 inhibitor does not have a hydrophobic core. The presence and unique topography of the five disulfide bridges suggests that they play important roles in maintaining the tertiary structure of the inhibitor. In addition, the side chains of several charged residues from electrostatic and hydrogen-bonding cascades, which also probably compensate for the lack of extensive secondary structures and a hydrophobic core. The reactive-site loop of this inhibitor displays a conformation that is characteristic of most serine proteinase inhibitors.

CONCLUSIONS

The structure of the C/E-1 inhibitor confirms that inhibitors from Ascaris suum belong to a novel family of proteinase inhibitors. It also provides conclusive evidence for the correct disulfide bridge connections. The C/E-1 inhibitor probably acts by a common inhibitory mechanism proposed for other substrate-like protein inhibitors of serine proteinases. The unusual molecular scaffolding presents a challenge to current folding algorithms. Proteins like the C/E-1 inhibitor may provide a valuable model system to study how the primary sequence of a protein dictates its three-dimensional structure.

The detection of AKH/HrTH-like peptides in Ascaridia galli and Ascaris suum using an insect hyperglycaemic bioassay

Evidence for the presence of adipokinetic hormone/hypertrehalosaemic hormone (AKH/HrTH)-like peptides in the parasitic nematodes Ascaridia galli and Ascaris suum has been obtained using insect bioassays which measure hyperglycaemic responses to peptides belonging to the AKH/HrTH family of insect hormones. A peptide fraction extracted from heads and tails of Ascaridia galli evoked a dose-dependent hyperglycaemic response when injected into the cockroach, Periplaneta americana. Maximal bioactivity was obtained with material that was equivalent to 38 mg (wet weight) of nematode. Bioactivity appeared to be highest in extracts from heads and tails of both male and female worms and could be fractionated into at least three peaks of hyperglycaemic activity by reversed-phase high-performance liquid chromatography. An extract from heads and tails of A. suum also evoked a hyperglycaemic response when injected into the cockroach, Blaberus discoidalis. The bioactivity was inactivated on incubation with pure endopeptidase 24.11, confirming the peptidic nature of the bioactive material. These results provide evidence for the existence of peptides related to the insect AKH/HrTH family of peptides in parasitic nematodes.

Immunocytochemical demonstration of peptidergic and serotoninergic components in the enteric nervous system of the roundworm, Ascaris suum (Nematoda, Ascaroidea)

The localization and distribution of neuropeptides and an indoleamine (serotonin or 5-hydroxytryptamine) in the enteric nervous system (ENS) of the pig roundworm, Ascaris suum, have been determined by the application of an indirect immunofluorescence technique in conjunction with confocal scanning laser microscopy. Whole-mount preparations of pharyngeal, intestinal and rectal regions were screened with antisera to 23 vertebrate peptides, 2 invertebrate peptides and serotonin (= 5-HT). Positive immunoreactivity (IR) was obtained with antisera to pancreatic polypeptide (PP), peptide YY (PYY), FMRFamide, gastrin and serotonin. The only IR observed in the ENS was that evident in the nerve supply to the pharynx and rectal region; no IR was associated with any region of the intestine. The most extensive patterns of IR occurred with antisera to PYY, FMRFamide and serotonin. In the pharyngeal component of the ENS, IR was evident in the lateral and dorsal longitudinal pharyngeal nerves, pharyngeal commissures, nerve plexus, and associated nerve cells and fibres. In contrast, the distribution of IR to the PP and gastrin antisera was more restricted and displayed a lower intensity of immunostaining. The other component of the ENS, the rectal enteric system, only yielded immunostaining to FMRFamide. The possible role of neuropeptides and serotonin in the nutritional biology of nematodes is discussed.