Predicted structure of a major Schistosoma mansoni eggshell protein

Schistosoma mansoni: the egg, biosynthesis of the shell and interaction with the host

The schistosome eggshell is a hardened and tanned structure made from cross-linked proteins. It is synthesized within the female worm from many different kinds of proteins and glycoproteins. Once the egg is released in the circulation, the outer surface of the eggshell is exposed and hence a direct site of interaction between the parasite and the host. The major eggshell protein is p14, but about one third of the eggshell is made from common cellular proteins, some of which are known to be immunogenic. This has many consequences for parasite-host interactions. However, so far, the eggshell has gained little attention from researchers. We will discuss the structure of the eggshell and its role in granuloma formation, host factor binding and egg excretion.

The proteome of the insoluble Schistosoma mansoni eggshell skeleton

In schistosomiasis, the majority of symptoms of the disease is caused by the eggs that are trapped in the liver. These eggs elicit an immune reaction that leads to the formation of granulomas. The eggshell, which is a rigid insoluble structure built from cross-linked proteins, is the site of direct interaction between the egg and the immune system. However, the exact protein composition of the insoluble eggshell was previously unknown. To identify the proteins of the eggshell of Schistosoma mansoni we performed LC-MS/MS analysis, immunostaining and amino acid analysis on eggshell fragments. For this, eggshell protein skeleton was prepared by thoroughly cleaning eggshells in a four-step stripping procedure of increasing strength including urea and SDS to remove all material that is not covalently linked to the eggshell itself, but is part of the inside of the egg, such as Reynold's layer, von Lichtenberg's envelope and the miracidium. We identified 45 proteins of which the majority are non-structural proteins and non-specific for eggs, but are house-keeping proteins that are present in large quantities in worms and miracidia. Some of these proteins are known to be immunogenic, such as HSP70, GST and enolase. In addition, a number of schistosome-specific proteins with unknown function and no homology to any known annotated protein were found to be incorporated in the eggshell. Schistosome-specific glycoconjugates were also shown to be present on the eggshell protein skeleton. This study also confirmed that the putative eggshell protein p14 contributes largely to the eggshell. Together, these results give new insights into eggshell composition as well as eggshell formation. Those proteins that are present at the site and time of eggshell formation are incorporated in the cross-linked eggshell and this cross-linking does no longer occur when the miracidium starts secreting proteins.

An oligonucleotide microarray for transcriptome analysis of Schistosoma mansoni and its application/use to investigate gender-associated gene expression

Global profiling transcriptomes of parasitic helminths offers the potential to simultaneously identify co-ordinately expressed genes, novel genetic programs and uniquely utilized metabolic pathways, which together provide an extensive and new resource for vaccine and drug discovery. We have exploited this post-genomic approach to fabricate the first oligonucleotide DNA microarray for gene expression analysis of the parasitic trematode Schistosoma mansoni. A total of 17,329 S. mansoni DNA sequences were used to design a microarray consisting of 7335 parasite elements or approximately 50% of this parasite's transcriptome. Here, we describe the design of this new microarray resource and its evaluation by extending studies into gender-associated gene expression in adult schistosomes. We demonstrate a high degree of reproducibility in detecting transcriptional differences among biologically replicated experiments and the ability of the microarray to distinguish between the expression of closely related gene family members. Importantly, for issues related to sexual dimorphism, labour division, gamete production and drug target discovery, 197 transcripts demonstrated a gender-biased pattern of gene expression in the adult schistosome, greatly extending the number of sex-associated genes. These data demonstrate the power of this new resource to facilitate a greater understanding into the biological complexities of schistosome development and maturation useful for identifying novel intervention strategies.

An historical and genomic view of schistosome conjugal biology with emphasis on sex-specific gene expression

The genetic programmes associated with the sexual biology of dioecious schistosomes remain a critically important but significantly understudied area of parasitology. Throughout the last four decades, progress has been slow in describing the gross antigenic and proteomic differences linked to sexually mature schistosomes and in characterizing some of the sex-associated transcripts and regulatory mechanisms induced during developmental maturation. These investigations have been severely hindered by the lack of complete EST/genomic information, as well as corresponding post- and functional-genomic tools for studying these pathogenic parasites. As near complete transcriptomes forSchistosoma japonicumandS. mansonihave recently been reported, and both DNA microarrays and post-transcriptional gene silencing have been applied to schistosomes, the tools and techniques for the high-throughput identification and characterization of transcripts involved in conjugal biology are now readily available. Here, an historical review is presented that summarizes some of the most significant findings associated with schistosome sex and sexual maturation during the last several decades. Following this discussion is a current overview of some modern day genomic approaches used to study schistosomes, which illustrates how major advances in the field of conjugal biology will be achieved.

Characterization of development-related genes for the cestode Bothriocephalus acheilognathi

Differential gene expression of mature and immature Bothriocephalus acheilognathi cestodes was analyzed using the suppression subtractive hybridization technique. Five mature-associated cDNAs were isolated and characterized. Virtual Northern blot and RT-PCR analyses confirmed that four of the five genes were upregulated in mature parasites. The sequence analysis revealed that one gene encoded the structural protein chorion precursor, and the three encoded functional proteins homologous to yolk ferritin, sodium/hydrogen exchanger and muscin-like protein. Another gene appeared to be specific to B. acheilognathi, encoding a putative metal-bound protein. Although results obtained in the present study are preliminary, the information about the five genes may provide clues for further investigation on the decline in parasite numbers during the maturation of B. acheilognathi.

Gender-associated gene expression in two related strains of Schistosoma japonicum

Host inflammatory responses directed against eggs laid by sexually-mature Schistosoma japonicum female worms instigate lesion formation and associated clinical pathologies during infection. To identify parasite gene transcripts that associate with egg production and to characterise sexually-mature adult gene expression profiles of two related Chinese strains, S. japonicum cDNA microarrays were fabricated using 457 ESTs originating from three parasite developmental stages. Twenty-two female-associated and 8 male-associated gene transcripts were identified in the adult Anhui strain whereas 21 female-associated and 7 male-associated gene transcripts were revealed in the adult Zhejiang strain. RT-PCR analysis, in situ enzyme localisation studies and enzymatic assays confirmed the cDNA microarray results, and importantly, provided information previously unappreciated in schistosome conjugal biology. Specifically, our novel findings include the female-specific expression of genes putatively involved in haemoglobin digestion and eggshell formation including extracellular superoxide dismutase, two histidine-rich proteins, a large blood-brain barrier amino acid transporter and two tyrosinase orthologues. In contrast, transcripts involved in mechanical support (actin), cytoskeletal infrastructure (e.g. dynein light chain 3 and myosin regulatory light chain) and tegumental biology (e.g. TM4SF and Sj25) were more highly represented in adult male schistosomes. Together these data establish a transcriptional basis for adult schistosome labour division and expands the list of novel S. japonicum gender-associated gene transcripts that may be considered targets for improved intervention strategies.

Isolation of cDNAs encoding secreted and transmembrane proteins from Schistosoma mansoni by a signal sequence trap method

Surface and secreted proteins of schistosomes orchestrate the basic physiologic requirements of a parasitic existence. These proteins are often exposed to host tissues during penetration, migration, feeding, and immune evasion, and they are obvious targets for control strategies. Signal sequence trap (SST) represents a novel approach that selects for cDNAs encoding secreted and surface proteins with N-terminal signal peptides, so we constructed a randomly primed adult Schistosoma mansoni cDNA library fused to a signalless reporter gene encoding placental alkaline phosphatase. The library was used to transfect COS-7 cells, which were then assayed for the presence of reporter at the cell surface. Eighteen S. mansoni cDNA fragments were isolated and sequenced. Expression profiles of the novel clones were determined for different developmental stages; some transcripts were restricted to single-sex adult worms, while others were ubiquitously distributed. Most clones contained signal peptides or signal anchors as determined by the SignalP algorithm. Open reading frames (ORFs) were categorized as follows: (i) previously identified S. mansoni cDNAs encoding proteins of known function; (ii) cDNAs encoding proteins of known function in other organisms but novel for Schistosoma; (iii) S. mansoni expressed sequence tags (ESTs) of unknown function; and (iv) completely novel ORFs without homologues (including ESTs) from any phylum. Clones of particular interest included tetraspanins similar to human cell surface antigens, a protein kinase, and ORFs transcribed in the antisense orientation to previously characterized S. mansoni cDNAs. This is the first report describing the use of SST as a tool for identifying secreted proteins from any pathogenic organism.

A novel cDNA clone of Schistosoma japonicum encoding the 34,000 Dalton eggshell precursor protein

A cDNA clone encoding the 34 kDa eggshell protein of Schistosoma japonicum was isolated from an adult female cDNA library with a rabbit antiserum raised against the 34 kDa female worm fraction. A 230 bp-insert of this clone (Sj23A) was introduced in frame into the expression plasmid vector, pMAL-c2, and the recombinant fusion protein of the Sj23A transiation product was induced in Escherichia coli. The antiserum raised against the recombinant protein reacted only with the native 34 kDa protein of mature female worms, which localized in the vitelline cells of the vitelline glands. By reverse transcription-polymerase chain reaction (RT-PCR) analysis, it was found that the gene corresponding to the Sj23A was expressed exclusively in mature female worms. The clone Sj23A showed a high degree of homology to the genes for the eggshell precursor proteins of Fasciola hepatica. At the deduced polypeptide level, the Sj23A also had similarities with the F. hepatica-protein sequence, the amino acid composition [high glycine (16%), lysine (12%) and tyrosine (11%)] and the presence of tyrosine residues flanked by glycine. The clone Sj23A also shared an extensive sequence homology with 3 S. mansoni expression sequence tags (ESTs). The present results suggest that the protein encoded by the female-specific Sj23A gene of S. japonicum is widely conserved in trematodes and plays a significant role as a precursor involved in eggshell formation.

Electrophoretical and histochemical characterization of Schistosoma mansoni phenol oxidases

The phenol oxidase system, which is thought to play a central role in eggshell formation, was analyzed by means of electrophoretic and histochemical techniques. In contrast to current beliefs, our data show that males also express the phenol oxidase activity. The analysis of the electrophoretic pattern from males and females shows differences: adult males present a major band and a faint band, migrating slightly below. Adult females express a more complex pattern composed of four bands. Histochemical studies revealed that female phenol oxidase is concentrated in the vitelline cells, is inhibited by DDC, and this inhibition is correlated with disruption of female egg production. The present studies, in agreement with other reports, reveal that female phenol oxidase may be involved in sclerotization of the S. mansoni eggshell.

[Immunological aspects of the phenoloxidase enzymatic system of Schistosoma mansoni]

The phenol oxidase enzymatic system (EC 1.10.3.1, EC 1.10.3.2) is widespread in different species of the animal and vegetal kingdom. Despite its importance in the eggshell formation of the trematodes phenol oxidase (PO) has been little studied in these organisms, mainly in S. mansoni. This report presents the initial results concerning the immunization of rabbits with PO of S. mansoni and mushroom tyrosinase. The immunological analysis done by means of double immunodifusion (Ouchterlony) and immunoelectrophoresis techniques revealed some immunological identity between the PO of males and females. It was not seen cross reaction between the antisera against PO and tyrosinase, what suggests that the antigenic determinants of both enzymes are different in spite of their catalytic sites being similar, since they act over the same substrate. The results reported here represent a first step in way to obtain the PO isoenzymes in their pure form and should open new insights for further studies on the molecular mechanisms involved in the sclerotization process of the S. mansoni eggshell.

Structure of the gene encoding a putative Schistosoma mansoni tegumental antigen precursor

In order to obtain the complete gene encoding the putative precursor of a 15-kDa Schistosoma mansoni tegumental antigen (Sm15), two cDNAs (A70 and A184) and two fragments of independent genomic clones were subcloned and sequenced. The collated sequence contains 4700 nucleotides and represents the full length open reading frame of the gene, encoding a protein of 1032 amino acids with a calculated molecular mass of 116,900. Thus, the gene encodes a much longer protein than that identified in the tegumental membranes, suggesting that it encodes a precursor that is subsequently highly processed. A 964-bp region composed of 5 closely related repeats was found to be present within the translated frame. The predicted protein is highly acidic and there is no indication of hydrophobic domains that may represent transmembrane regions or indicate attachment of a GPI anchor. The coding region has no homologies in the currently available data bases. In the 5' non-transcribed area a copy of the SM alpha repeat family is present. The coding region is preceded by putative CCAAT and TATA boxes that may be involved in the control of expression.

Paternity testing with the F10 multilocus DNA fingerprinting probe

Empirical analysis of 200 paternity cases by multilocus DNA fingerprinting with the F10 probe showed that it was capable of distinguishing fathers from non-fathers in every case. The average exclusion probability was 0.99998. A very effective discrimination parameter was the proportion of non-maternal (test) bands which cannot be detected in the alleged father (unassignable bands) among all test bands. Values below 0.2 were seen in true fathers while in all cases of non-fathers the values were above 0.35. Minisatellite mutations occurred at a rate of 0.004 per band per child. The distribution of band-sharing among first degree relatives and unrelated individuals showed only a small overlap. Thus, band-sharing of the F10 fingerprints should provide a useful statistic for testing genetic relationships in deficiency cases.

DNA fingerprints: a tool for identification and determination of the relationships between species and strains of Leishmania

Using nonradioactive hybridization, the multilocal probes 33.15, F10 and (CAC)5 were shown to recognize multiple minisatellite regions in nuclear DNA of Leishmania, producing on Southern blots complex banding patterns typical of DNA fingerprints. We used the 33.15 probe to study 14 different strains belonging to 6 different species from both the sub-genus Viannia and the Leishmania mexicana complex of the sub-genus Leishmania. Distinct DNA fingerprints were obtained for each strain, permitting their identification. On the other hand, each strain showed little or no clonal variation. The information from the fingerprinting maps could be used for constructing phenograms and cladograms of the species and strains of Leishmania.

Molecular architecture of helicoidal proteinaceous eggshells

I will not attempt to summarize this chapter, which is already a summary. I merely wish to point out that experimental and theoretical evidence to date clearly suggests that antiparallel beta-pleated sheet dictates self-assembly in helicoidal proteinaceous eggshells. Molecular details of this process have started to become clear after the development of the specific, most probably correct, protein structural models in the case of the silkmoths, where amino acid information is available and with the help of several experimental techniques. However, for people seeking universal mechanisms the picture should still be far from complete. Several analogous systems should be studied before providing final answers.

Tandemly repeating peptide motifs and their secondary structure in Ceratitis capitata eggshell proteins Ccs36 and Ccs38

Evidence from amino acid composition, Fourier transform analysis of primary structure and secondary structure prediction suggests a tripartite structure for Ceratitis capitata eggshell proteins Ccs36 and Ccs38, which consists of a central domain and two flanking 'arms'. The proteins, apparently, contain tandemly repeating peptide motifs specific for each domain of the tripartite structure. The central domain of both proteins, which exhibits extensive sequence homology with the corresponding domains of Drosophila melanogaster proteins s36 and s38, is formed by tandem repeats of an octapeptide-X-X-X-Z-Z-Z-Z-Z- (where X = large hydrophobic residue and Z = beta-turn former residue) and its variants. It is predicted to adopt a compact, most probably twisted, antiparallel beta-pleated sheet structure of beta-sheet strands regularly alternating with beta-turns or loops. The central domains of Ccs36 and Ccs38 share structural similarities, but they are recognizably different. The 'arms' of the proteins presumably serving for protein and species-specific functions differ substantially from those of Drosophila melanogaster. In Ccs36, the C-terminal 'arm' is formed by, almost precise, tandem repeats of an octapeptide-Y-X-A-A-P-A-A-S- (X = G or S), whereas the N-terminal 'arm' contains repeats of the octapeptide -Z-Z-Z-A-X-A-A-Z- (X = Q, N or E and Z a beta-turn former). In both 'arms' alpha-helices are predicted, alternating with beta-turns.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a putative eggshell precursor protein of the female Schistosoma japonicum

In adult worms of Schistosoma japonicum, a prominent radiolabelled female-specific protein (34 kDa) was demonstrated on fluorography of SDS gels with the pulse incorporation of 14C-tyrosine in vitro, though it was difficult to detect major female-specific proteins by direct staining methods. This female-specific protein was demonstrated to localize exclusively in the vitelline cells by indirect immunofluorescence using the rabbit anti-34 kDa female protein antiserum. It was shown that 14C-tyrosine was selectively incorporated into the vitelline cells by the pulse labelled autoradiographs. Two days after the exposure of worms to radio-tyrosine, the shells of eggs in the uterus were demonstrated to have become radioactive, indicating that 14C-tyrosine-labelled protein was used as a material for the eggshell. In the fluorograph of proteins extracted from newly laid eggs in vitro, the prominent band was not found at the 34 kDa region, but a lot of radioactivity appeared at higher than 100 kDa. The results suggested that a 34 kDa female protein was a precursor of the eggshell and became a much larger protein molecule as a result of cross-linking during eggshell hardening.

An improved noninfectious murine skin model of organized granulomatous inflammation

An improved model of granulomatous inflammation in skin was developed by second passage skin grafting of isolated, lyophilized skin granulomas, originally elicited in naive mice by inoculations of lyophilized hepatic schistosome egg granulomas. The tissue reaction is caused by a single exposure to a noninfectious, acellular granulomagenic stimulus and occurs in healthy mice free of systemic disease. The model should prove useful for isolation of granuloma initiation factor(s). Furthermore, because there is a time lag before new granuloma formation begins, a window exists for analytical dissection of the initiation process. In this study we described the responses of host cells by autoradiography, and light and electron microscopy. The activity of angiotensin-converting enzyme and proline-specific endopeptidase showed a modulation during granuloma formation. In addition we found that severe immunosuppression with high dose cyclosporine therapy did not alter granuloma formation, supporting the idea that initiation of organized granulomas is T-cell independent.

DNA bioprints: simple nonisotopic DNA fingerprints with biotinylated probes

The discovery of multilocal DNA fingerprinting represented a revolution in criminal identification and paternity testing. However, for routine use in clinical laboratories, the standard DNA fingerprint methodology is too complex. We have been successful in the development of a simplified DNA nonisotopic fingerprinting system using biotin-labeled probes which we have called DNA bioprints. To achieve this we explored three main technical features: utilization of biotinylated nonradioactive probes as a simpler substitute for 32P-labeled probes, utilization of oligonucleotide probes as a simpler substitute for recombinant probes, and direct hybridization in the dried agarose gel as a simpler substitute for Southern blots. In this article we review our results in the development of DNA bioprints.

F10, the gene for the glycine-rich major eggshell protein of Schistosoma mansoni recognizes a family of hypervariable minisatellites in the human genome

Images

The phylogeny and chemical diversity of quinone-tanned glues and varnishes

1. 3,4-Dihydroxyphenyl-L-alanine (DOPA)-containing proteins are widely distributed throughout the animal kingdom and appear to serve chiefly as waterproof adhesives and varnishes. 2. The unique chemical and physical stability of these adhesives and varnishes is imparted by quinone-tanning, an oxidative process that leads to the polymerization of DOPA-containing and other proteins. 3. Recent advances in the biochemistry of DOPA-containing proteins suggest that most consist of tandemly repeated sequence motifs. Each motif contains DOPA, a basic amino acid (usually lysine), and abundant glycine or proline. 4. The DOPA residues undergo catechol oxidase-catalyzed conversion to o-quinones at the onset of quinone-tanning. 5. The complexity of quinone chemistry is discussed with regard to quinone-tanning.

Structural and functional features of Drosophila chorion proteins s36 and s38 from analysis of primary structure and infrared spectroscopy

Amino acid composition, Fourier transform analysis and secondary structure prediction methods strongly support a tripartite structure for Drosophila chorion proteins s36 and s38. Each protein consists of a central domain and two flanking 'arms'. The central domain contains tandemly repetitive peptides, which apparently generate a secondary structure of beta-sheet strands alternating with beta-turns, most probably, forming a twisted beta-pleated sheet or beta-barrel. The central domains of s36 and s38 share similarities, but they are recognizably different. The flanking 'arms', with different primary and secondary structure features, presumably serve protein-specific functions. The possible roles of the protein domains for the establishment of higher order structure in Drosophila chorion and the possible function of the molecules are discussed. The predicted secondary structure of Drosophila chorion proteins s36 and s38 is supported by experimental information obtained from Fourier transform infrared spectroscopic studies of Drosophila chorions.