Isolation and characterization of Perkinsus marinus proteases using bacitracin–sepharose affinity chromatography

Perkinsus marinus suppresses in vitro eastern oyster apoptosis via IAP-dependent and caspase-independent pathways involving TNFR, NF-kB, and oxidative pathway crosstalk

The protozoan parasite Perkinsus marinus causes Dermo disease in eastern oysters, Crassostrea virginica, and can suppress apoptosis of infected hemocytes using incompletely understood mechanisms. This study challenged hemocytes in vitro with P. marinus for 1 h in the presence or absence of caspase inhibitor Z-VAD-FMK or Inhibitor of Apoptosis protein (IAP) inhibitor GDC-0152. Hemocytes exposure to P. marinus significantly reduced granulocyte apoptosis, and pre-incubation with Z-VAD-FMK did not affect P. marinus-induced apoptosis suppression. Hemocyte pre-incubation with GDC-0152 prior to P. marinus challenge further reduced apoptosis of granulocytes with engulfed parasite, but not mitochondrial permeabilization. This suggests P. marinus-induced apoptosis suppression may be caspase-independent, affect an IAP-involved pathway, and occur downstream of mitochondrial permeabilization. P. marinus challenge stimulated hemocyte differential expression of oxidation-reduction, TNFR, and NF-kB pathways. WGCNA analysis of P. marinus expression in response to hemocyte exposure revealed correlated protease, kinase, and hydrolase expression that could contribute to P. marinus-induced apoptosis suppression.

Pathogen proteases and host protease inhibitors in molluscan infectious diseases

The development of infectious diseases represents an outcome of dynamic interactions between the disease-producing agent's pathogenicity and the host's self-defense mechanism. Proteases secreted by pathogenic microorganisms and protease inhibitors produced by host species play an important role in the process. This review aimed at summarizing major findings in research on pathogen proteases and host protease inhibitors that had been proposed to be related to the development of mollusk diseases. Metalloproteases and serine proteases respectively belonging to Family M4 and Family S8 of the MEROPS system are among the most studied proteases that may function as virulence factors in mollusk pathogens. On the other hand, a mollusk-specific family (Family I84) of novel serine protease inhibitors and homologues of the tissue inhibitor of metalloprotease have been studied for their potential in the molluscan host defense. In addition, research at the genomic and transcriptomic levels showed that more proteases of pathogens and protease inhibitor of hosts are likely involved in mollusk disease processes. Therefore, the pathological significance of interactions between pathogen proteases and host protease inhibitors in the development of molluscan infectious diseases deserves more research efforts.

Peptides having antimicrobial activity and their complexes with transition metal ions

Peptide antibiotics are produced by bacterial, mammalian, insect or plant organisms in defense against invasive microbial pathogens. Therefore, they are gaining importance as anti-infective agents. There are a number of antibiotics that require metal ions to function properly. Metal ions play a key role in their action and are involved in specific interactions with proteins, nucleic acids and other biomolecules. On the other hand, it is well known that some antimicrobial agents possess functional groups that enable them interacting with metal ions present in physiological fluids. Some findings support a hypothesis that they may alter the serum metal ions concentration in humans. Complexes usually have a higher positive charge than uncomplexed compounds. This means that they might interact more tightly with polyanionic DNA and RNA molecules. It has been shown that several metal ion complexes with antibiotics promote degradation of DNA. Some of them, such as bleomycin, form stable complexes with redox metal ions and split the nucleic acids chain via the free radicals mechanism. However, this is not a rule. For example blasticidin does not cause DNA damage. This indicates that some peptide antibiotics can be considered as ligands that effectively lower the oxidative activity of transition metal ions.

Identification of cvSI-3 and evidence for the wide distribution and active evolution of the I84 family of protease inhibitors in mollusks

Protease inhibitors are an extremely diverse group of proteins that control the proteolytic activities of proteases and play a crucial role in biological processes including host defenses. The I84 family of protease inhibitors in the MEROPS database currently consists of cvSI-1 and cvSI-2, two novel serine protease inhibitors purified and characterized from the eastern oyster Crassostrea virginica plasma and believed to play a role in host defense and disease resistance. In the present study, a third member of I84 family, named cvSI-3, was identified from C. virginica by cDNA cloning and sequencing. The full cvSI-3 cDNA was composed of 342 bp including a 255 bp open reading frame (ORF) that encodes an 84-amino acid peptide. The mature cvSI-3 molecule was predicted to have 68 amino acid residues after removal of a 16-amino acid signal peptide, with a calculated molecular mass of 7724.5 Da and a theoretical isoelectric point (pI) of 6.28. CvSI-3 amino acid sequence shared 41% identity with cvSI-2 and 37% identity with cvSI-1, which included 12 conserved cysteines. Quantitative real-time PCR determined that cvSI-3 gene expressed primarily in oyster digestive glands. Real-time PCR also detected that cvSI-1, cvSI-2 and cvSI-3 expression levels in digestive glands varied significantly, with cvSI-2 showing the highest expression level and cvSI-3 the lowest. Additionally, a significant correlation was detected between cvSI-2 and cvSI-3 mRNAs levels. Searches into sequence databases using cvSI-1, cvSI-2 and cvSI-3 as queries retrieved ESTs suggesting the possible existence of at least 9 more I84 family members in eastern oysters and of I84 family protease inhibitors in various bivalve and gastropod species. Moreover, orthologs of all C. virginica I84 family members or potential member genes were found to be present in the C. gigas genome, and their distributions among species provided important information about the evolution of the I84 family of protease inhibitors. It appears that the I84 family of protease inhibitors is widely distributed and actively evolving in the Phylum Mollusca.

Identification of MMV Malaria Box inhibitors of Perkinsus marinus using an ATP-based bioluminescence assay

"Dermo" disease caused by the protozoan parasite Perkinsus marinus (Perkinsozoa) is one of the main obstacles to the restoration of oyster populations in the USA. Perkinsus spp. are also a concern worldwide because there are limited approaches to intervention against the disease. Based on the phylogenetic affinity between the Perkinsozoa and Apicomplexa, we exposed Perkinsus trophozoites to the Medicines for Malaria Venture Malaria Box, an open access compound library comprised of 200 drug-like and 200 probe-like compounds that are highly active against the erythrocyte stage of Plasmodium falciparum. Using a final concentration of 20 µM, we found that 4 days after exposure 46% of the compounds were active against P. marinus trophozoites. Six compounds with IC50 in the µM range were used to compare the degree of susceptibility in vitro of eight P. marinus strains from the USA and five Perkinsus species from around the world. The three compounds, MMV666021, MMV665807 and MMV666102, displayed a uniform effect across Perkinsus strains and species. Both Perkinsus marinus isolates and Perkinsus spp. presented different patterns of response to the panel of compounds tested, supporting the concept of strain/species variability. Here, we expanded the range of compounds available for inhibiting Perkinsus proliferation in vitro and characterized Perkinsus phenotypes based on their resistance to six compounds. We also discuss the implications of these findings in the context of oyster management. The Perkinsus system offers the potential for investigating the mechanism of action of the compounds of interest.

Early host-pathogen interactions in marine bivalves: evidence that the alveolate parasite Perkinsus marinus infects through the oyster mantle during rejection of pseudofeces

Parasites have developed myriad strategies to reach and infect their specific hosts. One of the most common mechanisms for non-vector transmitted parasites to reach the internal host environment is by ingestion during feeding. In this study, we investigated the mechanisms of oyster host colonization by the alveolate Perkinsus marinus and focused on how oysters process infective waterborne P. marinus cells during feeding in order to determine the portal(s) of entry of this parasite to its host. We also compared the infectivity of freely-suspended cells of P. marinus with that of cells incorporated into marine aggregates to link changes in particle processing by the feeding organs with infection success and route. Finally, we evaluated the effect of oyster secretions (mucus) covering the feeding organs on P. marinus physiology because these host factors are involved in the processing of waterborne particles. The ensemble of results shows a unique mechanism for infection by which the parasite is mostly acquired during the feeding process, but not via ingestion. Rather, infection commonly occurs during the rejection of material as pseudofeces before reaching the mouth. The pseudofeces discharge area, a specialized area of the mantle where unwanted particles are accumulated for rejection as pseudofeces, showed significantly higher parasite loads than other host tissues including other parts of the mantle. Aggregated P. marinus cells caused significantly higher disease prevalence and infection intensities when compared to freely-suspended parasite cells. Mucus covering the mantle caused a quick and significant increase in parasite replication rates suggesting rapid impact on P. marinus physiology. A new model for P. marinus acquisition in oysters is proposed.

Molecular responses of Ostrea edulis haemocytes to an in vitro infection with Bonamia ostreae

Bonamiosis due to the parasite Bonamia ostreae is a disease affecting the flat oyster Ostrea edulis. B. ostreae is a protozoan, affiliated to the order of haplosporidia and to the cercozoan phylum. This parasite is mainly intracellular, infecting haemocytes, cells notably involved in oyster defence mechanisms. Suppression subtractive hybridisation (SSH) was carried out in order to identify oyster genes differentially expressed during an infection of haemocytes with B. ostreae. Forward and reverse banks allowed obtaining 1104 and 1344 clones respectively, among which 391 and 480 clones showed a differential expression between both tested conditions (haemocytes alone versus haemocytes in contact with parasites). ESTs of interest including genes involved in cytoskeleton, respiratory chain, detoxification membrane receptors, and immune system were identified. The open reading frames of two selected genes (galectin and IRF-like) were completely sequenced and characterized. Real time PCR assays were developed to study the relative expression of candidate ESTs during an in vitro infection of haemocytes by live and dead parasites. Haemocyte infection with B. ostreae induced an increased expression of omega glutathione S-transferase (OGST), superoxide dismutase (SOD), tissue inhibitor of metalloproteinase (TIMP), galectin, interferon regulatory factor (IRF-like) and filamin genes.

The Alveolate Perkinsus marinus: biological insights from EST gene discovery

Background

Perkinsus marinus, a protozoan parasite of the eastern oyster Crassostrea virginica, has devastated natural and farmed oyster populations along the Atlantic and Gulf coasts of the United States. It is classified as a member of the Perkinsozoa, a recently established phylum considered close to the ancestor of ciliates, dinoflagellates, and apicomplexans, and a key taxon for understanding unique adaptations (e.g. parasitism) within the Alveolata. Despite intense parasite pressure, no disease-resistant oysters have been identified and no effective therapies have been developed to date.

Results

To gain insight into the biological basis of the parasite's virulence and pathogenesis mechanisms, and to identify genes encoding potential targets for intervention, we generated >31,000 5' expressed sequence tags (ESTs) derived from four trophozoite libraries generated from two P. marinus strains. Trimming and clustering of the sequence tags yielded 7,863 unique sequences, some of which carry a spliced leader. Similarity searches revealed that 55% of these had hits in protein sequence databases, of which 1,729 had their best hit with proteins from the chromalveolates (E-value ≤ 1e-5). Some sequences are similar to those proven to be targets for effective intervention in other protozoan parasites, and include not only proteases, antioxidant enzymes, and heat shock proteins, but also those associated with relict plastids, such as acetyl-CoA carboxylase and methyl erythrithol phosphate pathway components, and those involved in glycan assembly, protein folding/secretion, and parasite-host interactions.

Conclusions

Our transcriptome analysis of P. marinus, the first for any member of the Perkinsozoa, contributes new insight into its biology and taxonomic position. It provides a very informative, albeit preliminary, glimpse into the expression of genes encoding functionally relevant proteins as potential targets for chemotherapy, and evidence for the presence of a relict plastid. Further, although P. marinus sequences display significant similarity to those from both apicomplexans and dinoflagellates, the presence of trans-spliced transcripts confirms the previously established affinities with the latter. The EST analysis reported herein, together with the recently completed sequence of the P. marinus genome and the development of transfection methodology, should result in improved intervention strategies against dermo disease.

Serine protease inhibitor cvSI-1 potential role in the eastern oyster host defense against the protozoan parasite Perkinsus marinus

The serine protease inhibitor cvSI-1, purified from plasma of eastern oysters, inhibited the proliferation of the protozoan parasite Perkinsus marinus in vitro. In situ hybridization located cvSI-1 gene expression in basophil cells of the digestive tubules and cvSI-1 expression measured by real-time quantitative reverse transcriptase polymerase chain reaction was several hundred folds greater in digestive glands than in other organs examined or circulating hemocytes. cvSI-1 gene expression was also significantly greater in winter than in summer. Finally, cvSI-1 gene expression and plasma protease inhibitory activity in oysters selected for increased resistance to P. marinus were significantly greater than in unselected oysters. These findings support the hypothesis that cvSI-1 plays a role in eastern oyster host defense against P. marinus possibly through inhibition of parasite proliferation.

Perkinsus marinus, a protozoan parasite of the eastern oyster, has a requirement for dietary sterols

Perkinsus marinus, a protozoan parasite of the eastern oyster, Crassostrea virginica, causes high mortality in its host along the Atlantic and Gulf coasts of North America. P. marinus meronts cultured in vitro in medium containing complete lipid supplement (cod liver oil, cholesterol and alpha tocopherol acetate in detergent) are able to synthesize a wide variety of lipids, yet cultures cannot be maintained in lipid-free medium. To determine P. marinus lipid requirements meronts were inoculated into media containing different combinations of lipid components in detergent. Treatments included complete lipid supplement (positive control), detergent only (negative control), cholesterol in detergent, alpha tocopherol acetate in detergent and cholesterol+alpha tocopherol acetate in detergent. Meronts proliferated in the positive control medium and media containing cholesterol or cholesterol+alpha tocopherol acetate, but failed to proliferate in the negative control medium and the medium containing just alpha tocopherol acetate. Gas chromatography analysis of P. marinus meronts grown in medium with added (13)C sodium acetate (0.5 mg mL(-1)) revealed the presence of fatty acids containing (13)C, but the only sterol present was cholesterol containing no (13)C. These results suggest that P. marinus cannot synthesize sterols and must sequester them from its host.

A novel slow-tight binding serine protease inhibitor from eastern oyster (Crassostrea virginica) plasma inhibits perkinsin, the major extracellular protease of the oyster protozoan parasite Perkinsus marinus

A serine protease inhibitor was purified from plasma of the eastern oyster, Crassostrea virginica. The inhibitor is a 7609.6 Da protein consisting of 71 amino acids with 12 cysteine residues that are postulated to form 6 intra-chain disulfide bridges. Sequencing of the cloned cDNA identified an open reading frame encoding a polypeptide of 90 amino acids, with the 19 N-terminal amino acids forming a signal peptide. No sequence similarity with known proteins was found in sequence databases. The protein inhibited the serine proteases subtilisin A, trypsin and perkinsin, the major extracellular protease of the oyster protozoan parasite, Perkinsus marinus, in a slow binding manner. The mechanism of inhibition involves a rapid binding of inhibitor to the enzyme to form a weak enzyme-inhibitor complex followed by a slow isomerization to form a very tight binding enzyme-inhibitor complex. The overall dissociation constants K(i) with subtilisin A, perkinsin and trypsin were 0.29 nM, 13.7 nM and 17.7 nM, respectively. No inhibition of representatives of the other protease classes was detected. This is the first protein inhibitor of proteases identified from a bivalve mollusk and it represents a new protease inhibitor family. Its tight binding to subtilisin and perkinsin suggests it plays a role in the oyster host defense against P. marinus.

Metalloantibiotic Mn(II)-bacitracin complex mimicking manganese superoxide dismutase

Superoxide dismutase (SOD) activities of various metallobacitracin complexes were evaluated using the riboflavin-methionine-nitro blue tetrazolium assay. The radical scavenging activity of various metallobacitracin complexes was shown to be higher than those of the negative controls, e.g., free transition metal ions and metal-free bacitracin. The SOD activity of the complex was found to be in the order of Mn(II)>Cu(II)>Co(II)>Ni(II). Furthermore, the effect of bacitracin and their complexation to metals on various microorganisms was assessed by antibiotic susceptibility testing. Moreover, molecular modeling and quantum chemical calculation of the metallobacitracin complex was performed to evaluate the correlation of electrostatic charge of transition metal ions on the SOD activity.

Monoclonal antibody analysis of Perkinsus marinus extracellular products

The protozoan oyster parasite Perkinsus marinus releases a complex set of extracellular products (ECP) during in vitro culture. These products have been previously implicated in parasite virulence, and their expression can be altered by medium supplementation with oyster tissue homogenate. Little is known regarding ECP function, regulation, or mechanism of storage and release. Perkinsus marinus ECP were purified from a protein-free medium and used to produce a panel of five monoclonal antibodies. Several of the antibodies recognised series of proteins implying that the ECP may originate from comparatively few parental molecules. The ECP are secreted by several pathways, including the release of one product from an external cell layer, and two other products from two morphologically distinct intracellular compartments. Antibodies against separate epitopes on one protein provided information about possible protein structure. A sandwich ELISA format allowed sensitive quantification of that protein and showed significantly reduced protein expression in oyster tissue homogenate supplemented cultures. Immunopurification allowed tandem mass spectroscopic amino acid sequencing of that protein. Another antibody was used to characterise the P. marinus cell wall. This antibody specifically bound to trophozoite and tomont walls, and was used to investigate the morphological and antigenic changes in these walls during Ray's fluid thioglycollate medium-induced formation of hypnospores. It was also used to confirm that oyster tissue homogenate supplementation could induce formation of hypnospores. This antibody labeled P. marinus cells in fixed oyster tissue in a species-specific manner.

Multiple Polymorphic Sites at the ITS and ATAN Loci in Cultured Isolates of Perkinsus marinus

Sequence analysis of genomic DNA from the protozoan parasite Perkinsus marinus at two loci revealed genetic polymorphisms within and among different cultured isolates. Genomic DNA from 12 Perkinsus marinus isolates was amplified at the internal transcribed spacer region and at an anonymous locus previously identified to contain polymorphisms by restriction fragment length polymorphism analysis. Fourteen polymorphic nucleotide positions were identified at the internal transcribed spacer region; eight in internal transcribed spacer 1 and six in internal transcribed spacer 2. Thirteen polymorphic nucleotide sites were identified within the anonymous locus. In some instances, more than three different sequences were observed at both the internal transcribed spacer region and at the anonymous locus from a single clonal isolate, suggesting the possibility of recombination in cultured cells and/or strand jumping during the polymerase chain reaction. Intra-isolate sequence variation (3.46% for the anonymous locus and 3.08% for internal transcribed spacer 1) was in several cases as high as inter-isolate sequence variation, even in one isolate where recombination was not evident. High intra- and inter-isolate variation detected at both loci demonstrates the importance of determining the genetic variation of each locus prior to development of sequence-based molecular diagnostics.

Protease activity in the plasma of American oysters, Crassostrea virginica, experimentally infected with the protozoan parasite Perkinsus marinus

Perkinsus marinus is responsible for disease and mortality of the American oyster, Crassostrea virginica. To investigate the interactions between P. marinus and oyster hemocytes, protease activity was measured in plasma of oysters collected 4 hr, 24 hr, 4 days, and 2 mo after experimental infection with P. marinus. A significant increase in protease activity was observed in oyster plasma 4 hr after injection with P. marinus, followed by a sharp decrease within 24 hr. Gelatin-impregnated gel electrophoresis showed the presence of 2 major bands (60 and 112 kDa) and 3 less prevalent bands (35, 92, and 200 kDa) with metalloproteinaselike activity in the plasma of noninfected oysters. Additional bands in the 40- to 60-kDa range, corresponding to P. marinus serine proteases, were observed in oyster plasma at early time points after infection. A transient, but significant, decrease in the activity of oyster metalloproteinases was observed at early time points after infection. Coincubation of oyster plasma with P. marinus extracellular products resulted in a decrease in oyster metalloproteinases and several P. marinus proteases. This study provides insights into the role of proteases in the pathogenesis of Dermo disease.

Metal binding and structure-activity relationship of the metalloantibiotic peptide bacitracin

Bacitracin is a widely used metallopeptide antibiotic produced by Bacillus subtilis and Bacillus licheniformis with a potent bactericidal activity directed primarily against Gram-positive organisms. This antibiotic requires a divalent metal ion such as Zn(2+) for its biological activity, and has been reported to bind several other transition metal ions, including Mn(2+), Co(2+), Ni(2+), and Cu(2+). Despite the widespread use of bacitracin since its discovery in the early 1940s, the structure-activity relationship of this drug has not been established and the coordination chemistry of its metal complexes was not fully determined until recently. This antibiotic has been suggested to influence cell functioning through more than one route. Since bacterial resistance against bacitracin is still rare despite several decades of widespread use, this antibiotic can serve as an ideal lead for the design of potent peptidyl antibiotics lacking bacterial resistance. In this review, the results of physical (including NMR, EPR, and EXAFS) and molecular biological studies regarding the synthesis and structure of bacitracin, the coordination chemistry of its metal derivatives, the mechanism of its antibiotic actions, its influence on membrane function, and its structure and function relationship are discussed.

Proteolytic activity of cultured Pseudoperkinsus tapetis extracellular products

Several pathogenic protozoan release proteases are necessary for host invasion and initiation of infection. We have identified proteolytic activities in extracellular proteins secreted by the clam parasite Pseudoperkinsus tapetis (Mesomycetozoa) in vitro. The protein concentration of the P. tapetis extracellular products (ECP) increased only during the first week of culture. The appearance of new proteins of 10 and 157 kDa at the second week sample and of 12 kDa at the third week sample was shown by SDS-PAGE. The protease activity rapidly increased in the first 3 weeks of culture, and five clear bands of 23, 29, 60, 67 and 96 kDa with proteolytic activity were detected in the ECP on gelatin SDS-PAGE. Using inhibitors, the proteases were identified as members of the Ca(2+) dependent, serine protease family. Their optimum pH was higher than pH 9.4. The protease activity of the P. tapetis ECP was different than that described for Perkinsus marinus, an oyster pathogen very similar morphologically to the clam parasite and member of the genus in which P. tapetis had been initially included.

Analysis of extracellular proteins of two Perkinsus spp. isolated from the softshell clam Mya arenaria in vitro

Biochemical characterization of the extracellular proteins (ECP) of two softshell clam Perkinsus spp. cloned isolates, Perkinsus chesapeaki isolate G-117 and Perkinsus marinus H-49, was performed and compared to that of the oyster-derived P. marinus isolate P-1. G-117 and H-49 demonstrated distinct differences in enzyme activities; however, all three isolates shared common bands. Substrate-impregnated gels showed H-49 to possess proteolytic activities while G-117 did not. Inhibition studies revealed that H-49 ECP contain serine proteases similar to those described for P-1. The G-117 ECP lacked proteolytic activity but showed a higher production of lipolytic enzymes than H-49 or P-1. Optimal in vitro growth temperatures for the two clam isolates were generally lower than those for P-1. G-117 showed faster growth at lower salinities than either H-49 or P-1. Clam Perkinsus spp. isolates appear to be better adapted to lower salinities and temperatures than the P. murinus isolate of the eastern oyster.