A cytochrome b561 with ferric reductase activity from the parasitic blood fluke, Schistosoma japonicum

Comparative transcriptomic analysis of the larval and adult stages of Dibothriocephalus dendriticus (Cestoda: Diphyllobothriidea)

Tapeworms of the genus Dibothriocephalus are widely distributed throughout the world, some of which are agents of human diphyllobothriasis, one of the most important fish-borne zoonoses caused by a cestode parasite. Genomic and transcriptomic data can be used to develop future diagnostic tools and epidemiological studies. The present work focuses on a comparative analysis of the transcriptomes of adult and plerocercoid D. dendriticus and the identification of their differentially expressed genes (DEGs). Transcriptome assembly and analysis yielded and annotated 35,129 unigenes, noting that 16,568 (47%) unigenes were not annotated in known databases, which may indicate a unique set of expressed transcripts for D. dendriticus. A total of 8022 differentially expressed transcripts were identified, including 3225 upregulated and 4797 downregulated differentially expressed transcripts from the plerocercoid and adult animals. The analysis of DEGs has shown that among the most differentially expressed genes, there are important genes characteristic of each stage. Thus, several genes are characteristic of D. dendriticus plerocercoids, including fatty acid-binding protein and ferritin. Among the most highly expressed DEGs of the adult stage of D. dendriticus is the Kunitz-type serine protease inhibitor, in two putative isoforms. The analyses of GO and KEGG metabolic pathways revealed that a large number of the DEGs of D. dendriticus are associated with the biosynthesis of various substances such as arginine and folate, as well as with various metabolic pathways such as galactose metabolism, selenocompound metabolism, and phosphonate and phosphinate metabolism. This will contribute to further research aimed at identifying targets for new generation drugs and the development of specific vaccines.

A new ferritin SjFer0 affecting the growth and development of Schistosoma japonicum

Background

Schistosomiasis, an acute and chronic parasitic disease, causes substantial morbidity and mortality in tropical and subtropical regions of the world. Iron is an essential constituent of numerous macromolecules involving in important cellular reactions in virtually all organisms. Trematodes of the genus Schistosoma live in iron-rich blood, feed on red blood cells and store abundant iron in vitelline cells. Ferritins are multi-meric proteins that store iron inside cells. Three ferritin isoforms in Schistosoma japonicum are known, namely SjFer0, SjFer1 and SjFer2; however, their impact on the growth and development of the parasites  is still unknown. In this study we report on and characterize the ferritins in S. japonicum.

Methods

A phylogenetic tree of the SjFer0, SjFer1 and SjFer2 genes was constructed to show the evolutionary relationship among species of genus Schistosoma. RNA interference in vivo was used to investigate the impact of SjFer0 on schistosome growth and development.  Immunofluorescence assay was applied  to localize the expression of the ferritins. RNA-sequencing was performed  to characterize the iron transport profile after RNA interference.

Results

SjFer0 was found to have low similarity with SjFer1 and SjFer2 and contain an additional signal peptide sequence. Phylogenetic analysis revealed that SjFer0 can only cluster with some ferritins of other trematodes and tapeworms, suggesting that this ferritin branch might be unique to these parasites. RNA interference in vivo showed that SjFer0 significantly affected the growth and development of schistosomula but did not affect egg production of adult female worms. SjFer1 and SjFer2 had no significant impact on growth and development. The immunofluorescence study showed that SjFer0 was widely expressed in the somatic cells and vitelline glands but not in the testicle or ovary. RNA-sequencing indicated  that, in female, the ion transport process and calcium ion binding function were downregulated after SjFer0 RNA interference. Among the differentially downregulated genes, Sj-cpi-2, annexin and insulin-like growth factor-binding protein may be accounted for the suppression of schistosome growth and development.

Conclusions

The results indicate that SjFer0 affects the growth and development of schistosomula but does not affect egg production of adult female worms. SjFer0 can rescue the growth of the fet3fet4 double mutant Saccharomyces cerevisiae (strain DEY1453), suggesting being able to promote iron absorption. The RNA interference of SjFer0 inferred that  the suppression of worm growth and development may via  down-regulating Sj-cpi-2, annexin, and IGFBP.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05247-1.

The transferred translocases: An old wine in a new bottle

The role of translocases was underappreciated and was not included as a separate class in the enzyme commission until August 2018. The recent research interests in proteomics of orphan enzymes, ionomics, and metallomics along with high-throughput sequencing technologies generated overwhelming data and revamped this enzyme into a separate class. This offers a great opportunity to understand the role of new or orphan enzymes in general and specifically translocases. The enzymes belonging to translocases regulate/permeate the transfer of ions or molecules across the membranes. These enzyme entries were previously associated with other enzyme classes, which are now transferred to a new enzyme class 7 (EC 7). The entries that are reclassified are important to extend the enzyme list, and it is the need of the hour. Accordingly, there is an upgradation of entries of this class of enzymes in several databases. This review is a concise compilation of translocases with reference to the number of entries currently available in the databases. This review also focuses on function as well as dysfunction of translocases during normal and disordered states, respectively.

Eudiplozoon nipponicum (Monogenea, Diplozoidae) and its adaptation to haematophagy as revealed by transcriptome and secretome profiling

Background

Ectoparasites from the family Diplozoidae (Platyhelminthes, Monogenea) belong to obligate haematophagous helminths of cyprinid fish. Current knowledge of these worms is for the most part limited to their morphological, phylogenetic, and population features. Information concerning the biochemical and molecular nature of physiological processes involved in host–parasite interaction, such as evasion of the immune system and its regulation, digestion of macromolecules, suppression of blood coagulation and inflammation, and effect on host tissue and physiology, is lacking. In this study, we report for the first time a comprehensive transcriptomic/secretome description of expressed genes and proteins secreted by the adult stage of Eudiplozoon nipponicum (Goto, 1891) Khotenovsky, 1985, an obligate sanguivorous monogenean which parasitises the gills of the common carp (Cyprinus carpio).

Results

RNA-seq raw reads (324,941 Roche 454 and 149,697,864 Illumina) were generated, de novo assembled, and filtered into 37,062 protein-coding transcripts. For 19,644 (53.0%) of them, we determined their sequential homologues. In silico functional analysis of E. nipponicum RNA-seq data revealed numerous transcripts, pathways, and GO terms responsible for immunomodulation (inhibitors of proteolytic enzymes, CD59-like proteins, fatty acid binding proteins), feeding (proteolytic enzymes cathepsins B, D, L1, and L3), and development (fructose 1,6-bisphosphatase, ferritin, and annexin). LC-MS/MS spectrometry analysis identified 721 proteins secreted by E. nipponicum with predominantly immunomodulatory and anti-inflammatory functions (peptidyl-prolyl cis-trans isomerase, homolog to SmKK7, tetraspanin) and ability to digest host macromolecules (cathepsins B, D, L1).

Conclusions

In this study, we integrated two high-throughput sequencing techniques, mass spectrometry analysis, and comprehensive bioinformatics approach in order to arrive at the first comprehensive description of monogenean transcriptome and secretome. Exploration of E. nipponicum transcriptome-related nucleotide sequences and translated and secreted proteins offer a better understanding of molecular biology and biochemistry of these, often neglected, organisms. It enabled us to report the essential physiological pathways and protein molecules involved in their interactions with the fish hosts.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07589-z.

Functional Assembly of Caenorhabditis elegans Cytochrome b-2 (Cecytb-2) into Phospholipid Bilayer Nanodisc with Enhanced Iron Reductase Activity

Among seven homologs of cytochrome b₅₆₁ in a model organism C. elegans, Cecytb-2 was confirmed to be expressed in digestive organs and was considered as a homolog of human Dcytb functioning as a ferric reductase. Cecytb-2 protein was expressed in Pichia pastoris cells, purified, and reconstituted into a phospholipid bilayer nanodisc. The reconstituted Cecytb-2 in nanodisc environments was extremely stable and more reducible with ascorbate than in a detergent-micelle state. We confirmed the ferric reductase activity of Cecytb-2 by analyzing the oxidation of ferrous heme upon addition of ferric substrate under anaerobic conditions, where clear and saturable dependencies on the substrate concentrations following the Michaelis–Menten equation were observed. Further, we confirmed that the ferric substrate was converted to a ferrous state by using a nitroso-PSAP assay. Importantly, we observed that the ferric reductase activity of Cecytb-2 became enhanced in the phospholipid bilayer nanodisc.

Haem uptake is essential for egg production in the haematophagous blood fluke of humans, Schistosoma mansoni

Schistosomes ingest host erythrocytes, liberating large quantities of haem. Despite its toxicity, haem is an essential factor for numerous biological reactions, and may be an important iron source for these helminths. We used a fluorescence haem analogue, palladium mesoporphyrin, to investigate pathways of haem acquisition, and showed that palladium mesoporphyrin accumulates in the vitellaria (eggshell precursor glands) and ovary of female Schistosoma mansoni. Furthermore, incubation of adult females in 10-100 μm cyclosporin A (IC50 = 2.3 μm) inhibits the uptake of palladium mesoporphyrin to these tissues, with tenfold reductions in fluorescence intensity of the ovary. In vitro exposure to cyclosporin A resulted in significant perturbation of egg production, reducing egg output from 34 eggs per female to 5.7 eggs per female over the incubation period, and retardation of egg development. We characterized a S. mansoni homologue of the haem-responsive genes of Caenorhabditis elegans. The gene (Smhrg-1) encodes a protein with a molecular weight of approximately 17 kDa. SmHRG-1 was able to rescue growth in haem transport-deficient HEM1Δ yeast. Transcriptional suppression of Smhrg-1 in adult S. mansoni worms resulted in significant delay in egg maturation, with 47% of eggs from transcriptionally suppressed worms being identified as immature compared with only 27% of eggs laid by control worms treated with firefly luciferase. Our findings indicate the presence of transmembrane haem transporters in schistosomes, with a high abundance of these molecules being present in tissues involved in oogenesis.

Antibody Signatures Reflect Different Disease Pathologies in Patients With Schistosomiasis Due to Schistosoma japonicum

Infection with Schistosoma japonicum causes high levels of pathology that is predominantly determined by the cellular and humoral response of the host. However, the specific antibody response that arises during the development of disease is largely undescribed in Asian schistosomiasis-endemic populations. A schistosome protein microarray was used to compare the antibody profiles of subjects with acute infection, with early or advanced disease associated with severe pathology, with chronic infection, and subjects exposed but stool negative for S. japonicum eggs to the antibody profiles of nonexposed controls. Twenty-five immunodominant antigens were identified, including vaccine candidates, tetraspanin-related proteins, transporter molecules, and unannotated proteins. Additionally, individuals with severe pathology had a limited specific antibody response, suggesting that individuals with mild disease may use a broad and strong antibody response, particularly against surface-exposed proteins, to control pathology and/or infection. Our study has identified specific antigens that can discriminate between S. japonicum-exposed groups with different pathologies and may also allow the host to control disease pathology and provide resistance to parasite infection.

Characterization and differential expression of a ferritin protein from Fasciola hepatica

Ferritins are proteins that play a central role in maintaining intracellular iron balance. A cDNA clone of Fasciola hepatica (687 bp long) encoding a putative 228-amino acid polypeptide (FhFtn-1) homologous with ferritins of vertebrates and invertebrates was identified. FhFtn-1 contains a conserved motif of the ferroxidase center typical of vertebrate ferritins. Phylogenetic tree analysis showed that FhFtn-1 clusters with two ferritins of Paragonimus westermani, which suggests a common ancestry for the ferritins of these two trematodes. Recombinant FhFtn-1 protein expressed and purified from an Escherichia coli system showed iron-uptake ability. Moreover, FhFtn-1 showed strong reactivity with sera from rabbits infected with F. hepatica for 2-12 weeks, which suggests that this protein could be a potential antigen for immunodiagnosis of fascioliasis. qPCR analysis demonstrated that FhFtn-1-mRNA is expressed at significantly higher levels in adults and unembryonated eggs than in juveniles or miracidia. These results represent the first characterization of a ferritin protein from the liver fluke F. hepatica.

The Bradyrhizobium japonicum frcB gene encodes a diheme ferric reductase

Iron utilization by bacteria in aerobic environments involves uptake as a ferric chelate from the environment, followed by reduction to the ferrous form. Ferric iron reduction is poorly understood in most bacterial species. Here, we identified Bradyrhizobium japonicum frcB (bll3557) as a gene adjacent to, and coregulated with, the pyoR gene (blr3555) encoding the outer membrane receptor for transport of a ferric pyoverdine. FrcB is a membrane-bound, diheme protein, characteristic of eukaryotic ferric reductases. Heme was essential for FrcB stability, as were conserved histidine residues in the protein that likely coordinate the heme moieties. Expression of the frcB gene in Escherichia coli conferred ferric reductase activity on those cells. Furthermore, reduced heme in purified FrcB was oxidized by ferric iron in vitro. B. japonicum cells showed inducible ferric reductase activity in iron-limited cells that was diminished in an frcB mutant. Steady-state levels of frcB mRNA were strongly induced under iron-limiting conditions, but transcript levels were low and unresponsive to iron in an irr mutant lacking the global iron response transcriptional regulator Irr. Thus, Irr positively controls the frcB gene. FrcB belongs to a family of previously uncharacterized proteins found in many proteobacteria and some cyanobacteria. This suggests that membrane-bound, heme-containing ferric reductase proteins are not confined to eukaryotes but may be common in bacteria.

Molecular analysis of zinc transporters in Schistosoma japonicum

Members of the zinc-regulated transporter/iron-regulated transporter-like protein (ZIP) family of proteins transport metal ions across cell membranes. Genes encoding ZIPs are present in the genomes of schistosomes. Here, we describe molecular characterisation of six ZIPs (SjZIPA-F) from Schistosoma japonicum. Quantitative PCR analyses of these ZIPs through the lifecycle showed that each is expressed predominantly during the intramammalian stage and are particularly enriched in adult females. Using laser microdissected tissue as template, SjZIPA-D were transcriptionally enriched in female reproductive tissues, SjZIPE was not expressed in specific tissues and SjZIPF was expressed similarly in each tissue. Whole mount in situ hybridization revealed that SjZIPA and SjZIPB were localised to the oesophageal gland of adults and the vitellaria. We have shown that multiple ZIPs are expressed by schistosomes during the intramammalian parasitic phases and propose that the encoded products perform diverse cellular functions related to metal transport in different cells of S. japonicum.