Milleporin-1, a new phospholipase A2 active protein from the fire coral Millepora platyphylla nematocysts

Transcriptomic and proteomic analyses reveal the first occurrence of diverse toxin groups in Millepora alcicornis

Millepora alcicornis is a reef-forming cnidarian widely distributed in the Mexican Caribbean. Millepora species or "fire corals" inflict a painful stinging reaction in humans when touched. Even though hundreds of organic and polypeptide toxins have been characterized from sea anemones and jellyfish, there are few reports regarding the diversity of toxins synthesized by fire corals. Here, based on transcriptomic analysis of M. alcicornis, several predicted proteins that show amino acid sequence similarity to toxins were identified, including neurotoxins, metalloproteases, hemostasis-impairing toxins, serin proteases, cysteine-rich venom proteins, phospholipases, complement system-impairing toxins, phosphodiesterases, pore-forming toxins, and L-aminoacid oxidases. The soluble nematocyst proteome of this organism was shown to induce hemolytic, proteolytic, and phospholipase A2 effects by gel zymography. Protein bands or spots on 1D- and 2D-PAGE gels corresponding to zones of hemolytic and enzymatic activities were excised, subjected to in-gel digestion with trypsin, and analyzed by mass spectrometry. These proteins exhibited sequence homology to PLA2s, metalloproteinases, pore-forming toxins, and neurotoxins, such as actitoxins and CrTX-A. The complex array of venom-related transcripts that were identified in M. alcicornis, some of which are first reported in "fire corals", provide novel insight into the structural richness of Cnidarian toxins and their distribution among species. SIGNIFICANCE: Marine organisms are a promising source of bioactive compounds with valuable contributions in diverse fields such as human health, pharmaceuticals, and industrial application. Currently, not much attention has been paid to the study of fire corals, which possess a variety of molecules that exhibit diverse toxic effects and therefore have great pharmaceutical and biotechnological potential. The isolation and identification of novel marine-derived toxins by classical approaches are time-consuming and have low yields. Thus, next-generation strategies, like base-'omics technologies, are essential for the high-throughput characterization of venom compounds such as those synthesized by fire corals. This study moves the field forward because it provides new insights regarding the first occurrence of diverse toxin groups in Millepora alcicornis. The findings presented here will contribute to the current understanding of the mechanisms of action of Millepora toxins. This research also reveals important information related to the potential role of toxins in the defense and capture of prey mechanisms and for designing appropriate treatments for fire coral envenomation. Moreover, due to the lack of information on the taxonomic identification of Millepora, the insights presented here can advise the taxonomic classification of the species of this genus.

Biochemical and Toxinological Characterization of Venom from Macrorhynchia philippina (Cnidaria, Hydrozoa)

Macrorhynchia philippina is a colonial benthic hydroid from the Class Hydrozoa (Phylum Cnidaria) distributed in the tropical and subtropical marine waters from Atlantic Ocean, Indo-Pacific, and Mozambique. Its colonies somewhat resemble plants, causing confusion in the bathers who accidentally touch the animal. Acute burning/local pain, edema, erythema, and pruritus were symptoms already described, but its venom composition is unknown, as well as the participation of toxins for the symptom's development. Thus, herein, we show the biochemical composition and toxic effects of M. philippina venom. Colonies were collected and processed for histological analysis; alternatively, they were immersed into methanol containing 0.1% acetic acid for venom attainment, which was analyzed by mass spectrometry and submitted to edema and nociception evaluation in mice, hemolysis and antimicrobial assays in vitro. Before the molecule's extraction, it was possible to see the inoculation structures (hydrocladiums and hydrotheca) containing venom, which was released after the immersion of the animal in the solvents. The venom was composed mainly by low molecular mass compounds, able to cause significant reduction of the paw withdrawal latency from the hot plate test, 30 minutes after the injection. Moreover, significant edema was observed 10 and 30 minutes after the injection, indicating the activity of at least two inflammatory mediators. The venom caused no hemolytic activity but reduced the growth of A. baumannii and K. pneumoniae strains. This study is the first biochemical description of M. philippina venom, with molecules that cause fast inflammatory and painful effects, characteristic of the envenomation.

New Insights into the Toxin Diversity and Antimicrobial Activity of the “Fire Coral” Millepora complanata

To date, few studies have been carried out aimed at characterizing the toxins synthesized by hydrocorals of the genus Millepora. The purpose of this study was to explore the toxin diversity and antibacterial activity of the “fire coral” M. complanata using a transcriptomic data mining approach. In addition, the cytolytic and antibacterial activities of the M. complanata nematocyst proteome were experimentally confirmed. Cytolysins were predicted from the transcriptome by comparing against the Animal Toxin Annotation Project database, resulting in 190 putative toxins, including metalloproteases, hemostasis-impairing toxins, phospholipases, among others. The M. complanata nematocyst proteome was analyzed by 1D and 2D electrophoresis and zymography. The zymograms showed different zones of cytolytic activity: two zones of hemolysis at ~25 and ~205 kDa, two regions corresponding to phospholipase A2 (PLA2) activity around 6 and 25 kDa, and a proteolytic zone was observed between 50 and 205 kDa. The hemolytic activity of the proteome was inhibited in the presence of PLA2 and proteases inhibitors, suggesting that PLA2s, trypsin, chymotrypsin, serine-proteases, and matrix metalloproteases are responsible for the hemolysis. On the other hand, antimicrobial peptide sequences were retrieved from their transcripts with the amPEPpy software. This analysis revealed the presence of homologs to SK84, cgUbiquitin, Ubiquicidin, TroTbeta4, SPINK9-v1, and Histone-related antimicrobials in the transcriptome of this cnidarian. Finally, by employing disk diffusion and microdilution assays, we found that the nematocyst peptidome of M. complanata showed inhibitory activity against both Gram-positive and Gram-negative bacteria including S. enteritidis, P. perfectomarina, E. coli, and C. xerosis, among others. This is the first transcriptomic data mining analysis to explore the diversity of the toxins synthesized by an organism of the genus Millepora. Undoubtedly, this work provides information that will broaden our general understanding of the structural richness of cnidarian toxins.

A Review of Toxins from Cnidaria

Cnidarians have been known since ancient times for the painful stings they induce to humans. The effects of the stings range from skin irritation to cardiotoxicity and can result in death of human beings. The noxious effects of cnidarian venoms have stimulated the definition of their composition and their activity. Despite this interest, only a limited number of compounds extracted from cnidarian venoms have been identified and defined in detail. Venoms extracted from Anthozoa are likely the most studied, while venoms from Cubozoa attract research interests due to their lethal effects on humans. The investigation of cnidarian venoms has benefited in very recent times by the application of omics approaches. In this review, we propose an updated synopsis of the toxins identified in the venoms of the main classes of Cnidaria (Hydrozoa, Scyphozoa, Cubozoa, Staurozoa and Anthozoa). We have attempted to consider most of the available information, including a summary of the most recent results from omics and biotechnological studies, with the aim to define the state of the art in the field and provide a background for future research.

Damages at the nanoscale on red blood cells promoted by fire corals

The hydrocoral Millepora alcicornis, known as fire coral, biosynthesize protein toxins with phospholipase A2 (PLA2) activity as a main defense mechanism; proteins that rapidly catalyse the hydrolysis at the sn-2 position of phosphatidylcholine-type phospholipids of cellular membranes. This hydrolysis mechanism triggers a structural damage in the outer leaflet of the red blood cells (RBC) membrane, by generating pores in the lipid bilayer that leads to a depletion of the cellular content of the damaged cell. A secondary mechanism, tentatively caused by pore-forming proteins toxins (PFTs), has been observed. The use of atomic force microscopy (AFM) has allowed to visualize the evolution of damages produced on the surface of the cells at the nanoscale level along the time.

A Novel Phospholipase A2 Isolated from Palythoa caribaeorum Possesses Neurotoxic Activity

Zoanthids of the genus Palythoa are distributed worldwide in shallow waters around coral reefs. Like all cnidarians, they possess nematocysts that contain a large diversity of toxins that paralyze their prey. This work was aimed at isolating and functionally characterizing a cnidarian neurotoxic phospholipase named A2-PLTX-Pcb1a for the first time. This phospholipase was isolated from the venomous extract of the zoanthid Palythoa caribaeorum. This enzyme, which is Ca²⁺-dependent, is a 149 amino acid residue protein. The analysis of the A2-PLTX-Pcb1a sequence showed neurotoxic domain similitude with other neurotoxic sPLA₂´s, but a different catalytic histidine domain. This is remarkable, since A2-PLTX-Pcb1a displays properties like those of other known PLA₂ enzymes.

Functional Elucidation of Nemopilema nomurai and Cyanea nozakii Nematocyst Venoms' Lytic Activity Using Mass Spectrometry and Zymography

Background: Medusozoans utilize explosively discharging penetrant nematocysts to inject venom into prey. These venoms are composed of highly complex proteins and peptides with extensive bioactivities, as observed in vitro. Diverse enzymatic toxins have been putatively identified in the venom of jellyfish, Nemopilema nomurai and Cyanea nozakii, through examination of their proteomes and transcriptomes. However, functional examination of putative enzymatic components identified in proteomic approaches to elucidate potential bioactivities is critically needed. Methods: In this study, enzymatic toxins were functionally identified using a combined approach consisting of in gel zymography and liquid chromatography tandem mass spectrometry (LC-MS/MS). The potential roles of metalloproteinases and lipases in hemolytic activity were explored using specific inhibitors. Results: Zymography indicated that nematocyst venom possessed protease-, lipase- and hyaluronidase-class activities. Further, proteomic approaches using LC-MS/MS indicated sequence homology of proteolytic bands observed in zymography to extant zinc metalloproteinase-disintegrins and astacin metalloproteinases. Moreover, pre-incubation of the metalloproteinase inhibitor batimastat with N. nomurai nematocyst venom resulted in an approximate 62% reduction of hemolysis compared to venom exposed sheep erythrocytes, suggesting that metalloproteinases contribute to hemolytic activity. Additionally, species within the molecular mass range of 14–18 kDa exhibited both egg yolk and erythrocyte lytic activities in gel overlay assays. Conclusion: For the first time, our findings demonstrate the contribution of jellyfish venom metalloproteinase and suggest the involvement of lipase species to hemolytic activity. Investigations of this relationship will facilitate a better understanding of the constituents and toxicity of jellyfish venom.

Composition and biological activities of the aqueous extracts of three scleractinian corals from the Mexican Caribbean: Pseudodiploria strigosa, Porites astreoides and Siderastrea siderea

BACKGROUND

Scleractinian corals (stony corals) are the most abundant reef-forming cnidarians found in coral reefs throughout the world. Despite their abundance and ecological importance, information about the diversity of their toxins and their biological activities is very scarce. In this study, the chemical composition and the biological activities of the aqueous extracts of Pseudodiploria strigosa, Porites astreoides and Siderastrea siderea, three scleractinian corals from the Mexican Caribbean, have been assessed for the first time.

METHODS

Toxicity of the extracts was assessed in crickets; the presence of cytolysins was detected by the hemolysis assay; the vasoconstrictor activity was determined by the isolated rat aortic ring assay; the nociceptive activity was evaluated by the formalin test. The presence of phospholipases A₂ (PLA₂), serine proteases, and hyaluronidases was determined by enzymatic methods. Low-molecular-weight fractions were obtained by gel filtration chromatography and ultrafiltration.

RESULTS

Extracts from the three species were toxic to crickets, induced hemolysis in human and rat erythrocytes, produced vasoconstriction on isolated rat aortic rings, and presented phospholipase A₂ and serine-protease activity. Despite the fact that these corals are not considered to be harmless to humans, the extracts generated significant nociceptive responses. The matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry analysis of the low-molecular-weight fractions revealed the presence of peptides within a mass range of 3000 to 6000 Da. These fractions were toxic to crickets and two of them induced a transitory vasoconstrictor effect on isolated rat aortic rings.

CONCLUSION

This study suggests that scleractinian corals produce low-molecular-weight peptides that are lethal to crickets and induce vasoconstriction.

Gene duplications are extensive and contribute significantly to the toxic proteome of nematocysts isolated from Acropora digitifera (Cnidaria: Anthozoa: Scleractinia)

Background

Gene duplication followed by adaptive selection is a well-accepted process leading to toxin diversification in venoms. However, emergent genomic, transcriptomic and proteomic evidence now challenges this role to be at best equivocal to other processess . Cnidaria are arguably the most ancient phylum of the extant metazoa that are venomous and such provide a definitive ancestral anchor to examine the evolution of this trait.

Methods

Here we compare predicted toxins from the translated genome of the coral Acropora digitifera to putative toxins revealed by proteomic analysis of soluble proteins discharged from nematocysts, to determine the extent to which gene duplications contribute to venom innovation in this reef-building coral species. A new bioinformatics tool called HHCompare was developed to detect potential gene duplications in the genomic data, which is made freely available (https://github.com/rgacesa/HHCompare).

Results

A total of 55 potential toxin encoding genes could be predicted from the A. digitifera genome, of which 36 (65 %) had likely arisen by gene duplication as evinced using the HHCompare tool and verified using two standard phylogeny methods. Surprisingly, only 22 % (12/55) of the potential toxin repertoire could be detected following rigorous proteomic analysis, for which only half (6/12) of the toxin proteome could be accounted for as peptides encoded by the gene duplicates. Biological activities of these toxins are dominatedby putative phospholipases and toxic peptidases.

Conclusions

Gene expansions in A. digitifera venom are the most extensive yet described in any venomous animal, and gene duplication plays a significant role leading to toxin diversification in this coral species. Since such low numbers of toxins were detected in the proteome, it is unlikely that the venom is evolving rapidly by prey-driven positive natural selection. Rather we contend that the venom has a defensive role deterring predation or harm from interspecific competition and overgrowth by fouling organisms. Factors influencing translation of toxin encoding genes perhaps warrants more profound experimental consideration.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1976-4) contains supplementary material, which is available to authorized users.

Cytolytic and systemic toxic effects induced by the aqueous extract of the fire coral Millepora alcicornis collected in the Mexican Caribbean and detection of two types of cytolisins

BACKGROUND

Millepora alcicornis is a branching hydrocoral common throughout the Caribbean Sea. Like other members of this genus, this species is capable of inducing skin eruptions and blisters with severe pain after contact. In the present study, we investigated the toxicity of the M. alcicornis aqueous extract on several animal models. Considering that some cnidarian hemolysins have been associated to local tissue damage, since they also induce lysis of other cell types, we also made a partial characterization of the hemolytic activity of M. alcicornis aqueous extract. This information is important for understanding the defense mechanisms of the "fire corals".

METHODS

The effects of pH, temperature, and some divalent cations on the hemolytic activity of the extract were assayed, followed by a zymogram analysis to detect the cytolysins and determine their approximate molecular weight. The toxicity of the aqueous extract was assayed in mice, by intravenous administration, and histopathological changes on several tissues were analyzed by light microscopy. The toxicity of the extract was also tested in Artemia salina nauplii, and the damages caused on the crustaceans were analyzed by transmission and scanning electron microscopy.

RESULTS

The hemolytic activity of the hydrocoral extract was enhanced in the presence of Ca(2+) (≥2 mM), Mg(2+) (≥6 mM), and Ba(2+) (≥0.1 mM); however, it was reduced in the presence of Cu(2+) (≥0.1 mM), Zn(2+) (≥6 mM), and EDTA (≥0.34 mM). Differences in the pH did not affect the hemolytic activity, but it was temperature-sensitive, since preincubation at ≥ 50 °C sharply reduced hemolysis. The zymogram showed the presence of two types of hemolysins: ~ 28-30 kDa proteins with phospholipase A2 activity and ~ 200 kDa proteins that do not elicit enzymatic activity. The aqueous extract of this cnidarian was lethal to mice (LD50 = 17 μg protein/g), and induced kidney, liver, and lung damages. Under denaturing conditions, the aqueous extract completely lost its toxic and hemolytic activities.

CONCLUSIONS

The results showed that the M. alcicornis aqueous extract contains two types of thermolabile hemolysins: proteins of approximately 28-30 kDa with PLA2 activity, while the others are larger proteins of approximately 200 kDa, which do not possess PLA2 activity. Those thermolabile cytolysins, which are stable to pH changes and whose activity is calcium dependent, are capable of inducing damage in lung, kidney and liver tissues, resulting in a slow death of mice. M. alcicornis cytolysins also provoke tissue dissociation in Artemia salina nauplii that might be attributed to pore forming mechanisms.

Characteristics of hemolytic activity induced by the aqueous extract of the Mexican fire coral Millepora complanata

BACKGROUND

Millepora complanata is a plate-like fire coral common throughout the Caribbean. Contact with this species usually provokes burning pain, erythema and urticariform lesions. Our previous study suggested that the aqueous extract of M. complanata contains non-protein hemolysins that are soluble in water and ethanol. In general, the local damage induced by cnidarian venoms has been associated with hemolysins. The characterization of the effects of these components is important for the understanding of the defense mechanisms of fire corals. In addition, this information could lead to better care for victims of envenomation accidents.

METHODS

An ethanolic extract from the lyophilized aqueous extract was prepared and its hemolytic activity was compared with the hemolysis induced by the denatured aqueous extract. Based on the finding that ethanol failed to induce nematocyst discharge, ethanolic extracts were prepared from artificially bleached and normal M. complanata fragments and their hemolytic activity was tested in order to obtain information about the source of the heat-stable hemolysins.

RESULTS

Rodent erythrocytes were more susceptible to the aqueous extract than chicken and human erythrocytes. Hemolytic activity started at ten minutes of incubation and was relatively stable within the range of 28-50°C. When the aqueous extract was preincubated at temperatures over 60°C, hemolytic activity was significantly reduced. The denatured extract induced a slow hemolytic activity (HU50 = 1,050.00 ± 45.85 μg/mL), detectable four hours after incubation, which was similar to that induced by the ethanolic extract prepared from the aqueous extract (HU50 = 1,167.00 ± 54.95 μg/mL). No significant differences were observed between hemolysis induced by ethanolic extracts from bleached and normal fragments, although both activities were more potent than hemolysis induced by the denatured extract.

CONCLUSIONS

The results showed that the aqueous extract of M. complanata possesses one or more powerful heat-labile hemolytic proteins that are slightly more resistant to temperature than jellyfish venoms. This extract also contains slow thermostable hemolysins highly soluble in ethanol that are probably derived from the body tissues of the hydrozoan.

High-molecular weight protein toxins of marine invertebrates and their elaborate modes of action

High-molecular weight protein toxins significantly contribute to envenomations by certain marine invertebrates, e.g., jellyfish and fire corals. Toxic proteins frequently evolved from enzymes meant to be employed primarily for digestive purposes. The cellular intermediates produced by such enzymatic activity, e.g., reactive oxygen species or lysophospholipids, rapidly and effectively mediate cell death by disrupting cellular integrity. Membrane integrity may also be disrupted by pore-forming toxins that do not exert inherent enzymatic activity. When targeted to specific pharmacologically relevant sites in tissues or cells of the natural enemy or prey, toxic enzymes or pore-forming toxins even may provoke fast and severe systemic reactions. Since toxin-encoding genes constitute "hot spots" of molecular evolution, continuous variation and acquirement of new pharmacological properties are guaranteed. This also makes individual properties and specificities of complex proteinaceous venoms highly diverse and inconstant. In the present chapter we portray high-molecular weight constituents of venoms present in box jellyfish, sea anemones, sea hares, fire corals and the crown-of-thorns starfish. The focus lies on the latest achievements in the attempt to elucidate their molecular modes of action.