Search Results (11)

Sea anemones are predatory marine invertebrates and have diverse venom arsenals. Venom is integral to their biology, and is used in competition, defense, and feeding. Three lineages of sea anemones are known to have independently evolved symbiotic relationships with clownfish, however the evolutionary impact of this relationship on the venom composition of the host is still unknown. Here, we investigate the potential of this symbiotic relationship to shape the venom profiles of the sea anemones that host clownfish. We use transcriptomic data to identify differences and similarities in venom profiles of six sea anemone species, representing the three known clades of clownfish-hosting sea anemones. We recovered 1121 transcripts matching verified toxins across all species, and show that hemolytic and hemorrhagic toxins are consistently the most dominant and diverse toxins across all species examined. These results are consistent with the known biology of sea anemones, provide foundational data on venom diversity of these species, and allow for a review of existing hierarchical structures in venomic studies. Full article

Actinoporins (APs) are soluble pore-forming proteins secreted by sea anemones that experience conformational changes originating in pores in the membranes that can lead to cell death. The processes involved in the binding and pore-formation of members of this protein family have been deeply examined in recent years; however, the intracellular responses to APs are only beginning to be understood. Unlike pore formers of bacterial origin, whose intracellular impact has been studied in more detail, currently, we only have knowledge of a few poorly integrated elements of the APs’ intracellular action. In this review, we present and discuss an updated landscape of the studies aimed at understanding the intracellular pathways triggered in response to APs attack with particular reference to sticholysin II, the most active isoform produced by the Caribbean Sea anemone Stichodactyla helianthus. To achieve this, we first describe the major alterations these cytolysins elicit on simpler cells, such as non-nucleated mammalian erythrocytes, and then onto more complex eukaryotic cells, including tumor cells. This understanding has provided the basis for the development of novel applications of sticholysins such as the construction of immunotoxins directed against undesirable cells, such as tumor cells, and the design of a cancer vaccine platform. These are among the most interesting potential uses for the members of this toxin family that have been carried out in our laboratory. Full article

A hallmark of sea anemone mitochondrial genomes (mitogenomes) is the presence of complex catalytic group I introns. Here, we report the complete mitogenome and corresponding transcriptome of the carpet sea anemone Stichodactyla haddoni (family Stichodactylidae). The mitogenome is vertebrate-like in size, organization, and gene content. Two mitochondrial genes encoding NADH dehydrogenase subunit 5 (ND5) and cytochrome c oxidase subunit I (COI) are interrupted with complex group I introns, and one of the introns (ND5-717) harbors two conventional mitochondrial genes (ND1 and ND3) within its sequence. All the mitochondrial genes, including the group I introns, are expressed at the RNA level. Nonconventional and optional mitochondrial genes are present in the mitogenome of S. haddoni. One of these gene codes for a COI-884 intron homing endonuclease and is organized in-frame with the upstream COI exon. The insertion-like orfA is expressed as RNA and translocated in the mitogenome as compared with other sea anemones. Phylogenetic analyses based on complete nucleotide and derived protein sequences indicate that S. haddoni is embedded within the family Actiniidae, a finding that challenges current taxonomy. Full article

Sea anemones are sedentary marine animals that tend to disperse via planktonic larvae and are predicted to have high population connectivity in undisturbed habitats. We test whether two sea anemone species living in two different tidal zones of a highly disturbed marine environment can maintain high genetic connectivity. More than 1000 loci with single-nucleotide polymorphisms (SNPs) were obtained with double-digest RADseq for 81 Stichodactyla haddoni and 99 Entacmaea quadricolor individuals to test for population genetic structure. We find evidence that both species predominantly propagate via sexual reproduction, and asexual reproduction is limited. We observe panmixia that indicates the absence of effective dispersal barriers for these species living in a highly anthropogenically disturbed environment. This is positive news for both species that are also found in the aquarium trade. More fundamentally, our results suggest that inhabiting different parts of a shallow reef may not affect a species’ population connectivity nor favour asexual reproduction. Full article

Venoms constitute complex mixtures of many different molecules arising from evolution in processes driven by continuous prey–predator interactions. One of the most common compounds in these venomous cocktails are pore-forming proteins, a family of toxins whose activity relies on the disruption of the plasmatic membranes by forming pores. The venom of sea anemones, belonging to the oldest lineage of venomous animals, contains a large amount of a characteristic group of pore-forming proteins known as actinoporins. They bind specifically to sphingomyelin-containing membranes and suffer a conformational metamorphosis that drives them to make pores. This event usually leads cells to death by osmotic shock. Sticholysins are the actinoporins produced by Stichodactyla helianthus. Three different isotoxins are known: Sticholysins I, II, and III. They share very similar amino acid sequence and three-dimensional structure but display different behavior in terms of lytic activity and ability to interact with cholesterol, an important lipid component of vertebrate membranes. In addition, sticholysins can act in synergy when exerting their toxin action. The subtle, but important, molecular nuances that explain their different behavior are described and discussed throughout the text. Improving our knowledge about sticholysins behavior is important for eventually developing them into biotechnological tools. Full article

Sea anemones’ venom is rich in peptides acting on different biological targets, mainly on cytoplasmic membranes and ion channels. These animals are also a source of pancreatic α-amylase inhibitors, which have the ability to control the glucose level in the blood and can be used for the treatment of prediabetes and type 2 diabetes mellitus. Recently we have isolated and characterized magnificamide (44 aa, 4770 Da), the major α-amylase inhibitor of the sea anemone Heteractis magnifica mucus, which shares 84% sequence identity with helianthamide from Stichodactyla helianthus. Herein, we report some features in the action of a recombinant analog of magnificamide. The recombinant peptide inhibits porcine pancreatic and human saliva α-amylases with Ki’s equal to 0.17 ± 0.06 nM and 7.7 ± 1.5 nM, respectively, and does not show antimicrobial or channel modulating activities. We have concluded that the main function of magnificamide is the inhibition of α-amylases; therefore, its functionally active recombinant analog is a promising agent for further studies as a potential drug candidate for the treatment of the type 2 diabetes mellitus. Full article

Sea anemones have been understudied as a source of peptide and protein toxins, with relatively few examined as a source of new pharmacological tools or therapeutic leads. This is surprising given the success of some anemone peptides that have been tested, such as the potassium channel blocker from Stichodactyla helianthus known as ShK. An analogue of this peptide, ShK-186, which is now known as dalazatide, has successfully completed Phase 1 clinical trials and is about to enter Phase 2 trials for the treatment of autoimmune diseases. One of the impediments to the exploitation of sea anemone toxins in the pharmaceutical industry has been the difficulty associated with their high-throughput discovery and isolation. Recent developments in multiple ‘omic’ technologies, including genomics, transcriptomics and proteomics, coupled with advanced bioinformatics, have opened the way for large-scale discovery of novel sea anemone toxins from a range of species. Many of these toxins will be useful pharmacological tools and some will hopefully prove to be valuable therapeutic leads. Full article

The bovine pancreatic trypsin inhibitor (BPTI)-Kunitz-type protein ShPI-1 (UniProt: P31713) is the major protease inhibitor from the sea anemone Stichodactyla helianthus. This molecule is used in biotechnology and has biomedical potential related to its anti-parasitic effect. A pseudo wild-type variant, rShPI-1A, with additional residues at the N- and C-terminal, has a similar three-dimensional structure and comparable trypsin inhibition strength. Further insights into the structure-function relationship of rShPI-1A are required in order to obtain a better understanding of the mechanism of action of this sea anemone peptide. Using enzyme kinetics, we now investigated its activity against other serine proteases. Considering previous reports of bifunctional Kunitz-type proteins from anemones, we also studied the effect of rShPI-1A on voltage-gated potassium (Kv) channels. rShPI-1A binds Kv1.1, Kv1.2, and Kv1.6 channels with IC₅₀ values in the nM range. Hence, ShPI-1 is the first member of the sea anemone type 2 potassium channel toxins family with tight-binding potency against several proteases and different Kv1 channels. In depth sequence analysis and structural comparison of ShPI-1 with similar protease inhibitors and Kv channel toxins showed apparent non-sequence conservation for known key residues. However, we detected two subtle patterns of coordinated amino acid substitutions flanking the conserved cysteine residues at the N- and C-terminal ends. Full article

Actinoporins are α-pore forming proteins with therapeutic potential, produced by sea anemones. Sticholysin II (StnII) from Stichodactyla helianthus is one of its most extensively characterized members. These proteins remain stably folded in water, but upon interaction with lipid bilayers, they oligomerize to form a pore. This event is triggered by the presence of sphingomyelin (SM), but cholesterol (Chol) facilitates pore formation. Membrane attachment and pore formation require changes involving long-distance rearrangements of residues located at the protein-membrane interface. The influence of Chol on membrane recognition, oligomerization, and/or pore formation is now studied using StnII variants, which are characterized in terms of their ability to interact with model membranes in the presence or absence of Chol. The results obtained frame Chol not only as an important partner for SM for functional membrane recognition but also as a molecule which significantly reduces the structural requirements for the mentioned conformational rearrangements to occur. However, given that the DOPC:SM:Chol vesicles employed display phase coexistence and have domain boundaries, the observed effects could be also due to the presence of these different phases on the membrane. In addition, it is also shown that the Arg51 guanidinium group is strictly required for membrane recognition, independently of the presence of Chol. Full article

ShK, from the sea anemone Stichodactyla helianthus, is a 35-residue disulfide-rich peptide that blocks the voltage-gated potassium channel Kv1.3 at ca. 10 pM and the related channel Kv1.1 at ca. 16 pM. We developed an analog of this peptide, ShK-186, which is currently in Phase 1b-2a clinical trials for the treatment of autoimmune diseases such as multiple sclerosis and rheumatoid arthritis. While ShK-186 displays a >100-fold improvement in selectivity for Kv1.3 over Kv1.1 compared with ShK, there is considerable interest in developing peptides with an even greater selectivity ratio. In this report, we describe several variants of ShK that incorporate p-phophono-phenylalanine at the N-terminus coupled with internal substitutions at Gln16 and Met21. In addition, we also explored the combinatorial effects of these internal substitutions with an alanine extension at the C-terminus. Their selectivity was determined by patch-clamp electrophysiology on Kv1.3 and Kv1.1 channels stably expressed in mouse fibroblasts. The peptides with an alanine extension blocked Kv1.3 at low pM concentrations and exhibited up to 2250-fold selectivity for Kv1.3 over Kv1.1. Analogs that incorporates p-phosphono-phenylalanine at the N-terminus blocked Kv1.3 with IC₅₀s in the low pM range and did not affect Kv1.1 at concentrations up to 100 nM, displaying a selectivity enhancement of >10,000-fold for Kv1.3 over Kv1.1. Other potentially important Kv channels such as Kv1.4 and Kv1.6 were only partially blocked at 100 nM concentrations of each of the ShK analogs. Full article

When 21 species of sea anemones were screened for Kv1 potassium channel toxins by competitive inhibition of the binding of ¹²⁵I-α-dendrotoxin to rat synaptosomal membranes, 11 species (two species of Actiniidae, one species of Hormathiidae, five species of Stichodactylidae and three species of Thalassianthidae) were found to be positive. Furthermore, full-length cDNAs encoding type 1 potassium channel toxins from three species of Stichodactylidae and three species of Thalassianthidae were cloned by a combination of RT-PCR, 3′RACE and 5′RACE. The precursors of these six toxins are commonly composed of signal peptide, propart and mature peptide portions. As for the mature peptide (35 amino acid residues), the six toxins share more than 90% sequence identities with one another and with κ_1.3-SHTX-She1a (Shk) from Stichodactyla helianthus but only 34–63% identities with the other type 1 potassium channel toxins. Full article