Structure-function relationships in ShKT domain peptides: ShKT-Ts1 from the sea anemone Telmatactis stephensoni.

Diverse structural scaffolds have been described in peptides from sea anemones, with the ShKT domain being a common scaffold first identified in ShK toxin from Stichodactyla helianthus. ShK is a potent blocker of voltage-gated potassium channels (KV 1.x), and an analog, ShK-186 (dalazatide), has completed Phase 1 clinical trials in plaque psoriasis. The ShKT domain has been found in numerous other species, but only a tiny fraction of ShKT domains has been characterized functionally. Despite adopting the canonical ShK fold, some ShKT peptides from sea anemones inhibit KV 1.x, while others do not. Mutagenesis studies have shown that a Lys-Tyr (KY) dyad plays a key role in KV 1.x blockade, although a cationic residue followed by a hydrophobic residue may also suffice. Nevertheless, ShKT peptides displaying an ShK-like fold and containing a KY dyad do not necessarily block potassium channels, so additional criteria are needed to determine whether new ShKT peptides might show activity against potassium channels. In this study, we used a combination of NMR and molecular dynamics (MD) simulations to assess the potential activity of a new ShKT peptide. We determined the structure of ShKT-Ts1, from the sea anemone Telmatactis stephensoni, examined its tissue localization, and investigated its activity against a range of ion channels. As ShKT-Ts1 showed no activity against KV 1.x channels, we used MD simulations to investigate whether solvent exposure of the dyad residues may be informative in rationalizing and potentially predicting the ability of ShKT peptides to block KV 1.x channels. We show that either a buried dyad that does not become exposed during MD simulations, or a partially exposed dyad that becomes buried during MD simulations, correlates with weak or absent activity against KV 1.x channels. Therefore, structure determination coupled with MD simulations, may be used to predict whether new sequences belonging to the ShKT family may act as potassium channel blockers.

Structural and functional characterisation of Tst2, a novel TRPV1 inhibitory peptide from the Australian sea anemone Telmatactis stephensoni.

Sea anemone venoms are complex mixtures of biologically active compounds, including disulfide-rich peptides, some of which have found applications as research tools, and others as therapeutic leads. Our recent transcriptomic and proteomic studies of the Australian sea anemone Telmatactis stephensoni identified a transcript for a peptide designated Tst2. Tst2 is a 38-residue peptide showing sequence similarity to peptide toxins known to interact with a range of ion channels (NaV, TRPV1, KV and CaV). Recombinant Tst2 (rTst2, which contains an additional Gly at the N-terminus) was produced by periplasmic expression in Escherichia coli, enabling the production of both unlabelled and uniformly 13C,15N-labelled peptide for functional assays and structural studies. The LC-MS profile of the recombinant Tst2 showed a pure peak with molecular mass 6 Da less than that of the reduced form of the peptide, indicating the successful formation of three disulfide bonds from its six cysteine residues. The solution structure of rTst2 was determined using multidimensional NMR spectroscopy and revealed that rTst2 adopts an inhibitor cystine knot (ICK) structure. rTst2 was screened using various functional assays, including patch-clamp electrophysiological and cytotoxicity assays. rTst2 was inactive against voltage-gated sodium channels (NaV) and the human voltage-gated proton (hHv1) channel. rTst2 also did not possess cytotoxic activity when assessed against Drosophila melanogaster flies. However, the recombinant peptide at 100 nM showed >50% inhibition of the transient receptor potential subfamily V member 1 (TRPV1) and slight (∼10%) inhibition of transient receptor potential subfamily A member 1 (TRPA1). Tst2 is thus a novel ICK inhibitor of the TRPV1 channel.

Next batter up! Targeting cancers with KRAS-G12D mutations.

KRAS is the most frequently mutated oncogene in cancer. Activating mutations in codon 12, especially G12D, have the highest prevalence across a range of carcinomas and adenocarcinomas. With inhibitors to KRAS-G12D now entering clinical trials, understanding the biology of KRAS-G12D cancers, and identifying biomarkers that predict therapeutic response is crucial. In this Review, we discuss the genomics and biology of KRAS-G12D adenocarcinomas, including histological features, transcriptional landscape, the immune microenvironment, and how these factors influence response to therapy. Moreover, we explore potential therapeutic strategies using novel G12D inhibitors, leveraging knowledge gained from clinical trials using G12C inhibitors.

Genomic, functional and structural analyses elucidate evolutionary innovation within the sea anemone 8 toxin family.

BACKGROUND: The ShK toxin from Stichodactyla helianthus has established the therapeutic potential of sea anemone venom peptides, but many lineage-specific toxin families in Actiniarians remain uncharacterised. One such peptide family, sea anemone 8 (SA8), is present in all five sea anemone superfamilies. We explored the genomic arrangement and evolution of the SA8 gene family in Actinia tenebrosa and Telmatactis stephensoni, characterised the expression patterns of SA8 sequences, and examined the structure and function of SA8 from the venom of T. stephensoni. RESULTS: We identified ten SA8-family genes in two clusters and six SA8-family genes in five clusters for T. stephensoni and A. tenebrosa, respectively. Nine SA8 T. stephensoni genes were found in a single cluster, and an SA8 peptide encoded by an inverted SA8 gene from this cluster was recruited to venom. We show that SA8 genes in both species are expressed in a tissue-specific manner and the inverted SA8 gene has a unique tissue distribution. While the functional activity of the SA8 putative toxin encoded by the inverted gene was inconclusive, its tissue localisation is similar to toxins used for predator deterrence. We demonstrate that, although mature SA8 putative toxins have similar cysteine spacing to ShK, SA8 peptides are distinct from ShK peptides based on structure and disulfide connectivity. CONCLUSIONS: Our results provide the first demonstration that SA8 is a unique gene family in Actiniarians, evolving through a variety of structural changes including tandem and proximal gene duplication and an inversion event that together allowed SA8 to be recruited into the venom of T. stephensoni.

Venoms for all occasions: The functional toxin profiles of different anatomical regions in sea anemones are related to their ecological function.

The phylum Cnidaria is the oldest extant venomous group and is defined by the presence of nematocysts, specialized organelles responsible for venom production and delivery. Although toxin peptides and the cells housing nematocysts are distributed across the entire animal, nematocyte and venom profiles have been shown to differ across morphological structures in actiniarians. In this study, we explore the relationship between patterns of toxin expression and the ecological roles of discrete anatomical structures in Telmatactis stephensoni. Specifically, using a combination of proteomic and transcriptomic approaches, we examined whether there is a direct correlation between the functional similarity of regions and the similarity of their associated toxin expression profiles. We report that the regionalization of toxin production is consistent with the partitioning of the ecological roles of venom across envenomating structures, and that three major functional regions are present in T. stephensoni: tentacles, epidermis and gastrodermis. Additionally, we find that most structures that serve similar functions not only have comparable putative toxin profiles but also similar nematocyst types. There was no overlap in the putative toxins identified using proteomics and transcriptomics, but the expression patterns of specific milked venom peptides were conserved across RNA-sequencing and mass spectrometry imaging data sets. Furthermore, based on our data, it appears that acontia of T. stephensoni may be transcriptionally inactive and only mature nematocysts are present in the distal portions of the threads. Overall, we find that the venom profile of different anatomical regions in sea anemones varies according to its ecological functions.

Tentacle Morphological Variation Coincides with Differential Expression of Toxins in Sea Anemones.

Phylum Cnidaria is an ancient venomous group defined by the presence of cnidae, specialised organelles that serve as venom delivery systems. The distribution of cnidae across the body plan is linked to regionalisation of venom production, with tissue-specific venom composition observed in multiple actiniarian species. In this study, we assess whether morphological variants of tentacles are associated with distinct toxin expression profiles and investigate the functional significance of specialised tentacular structures. Using five sea anemone species, we analysed differential expression of toxin-like transcripts and found that expression levels differ significantly across tentacular structures when substantial morphological variation is present. Therefore, the differential expression of toxin genes is associated with morphological variation of tentacular structures in a tissue-specific manner. Furthermore, the unique toxin profile of spherical tentacular structures in families Aliciidae and Thalassianthidae indicate that vesicles and nematospheres may function to protect branched structures that host a large number of photosynthetic symbionts. Thus, hosting zooxanthellae may account for the tentacle-specific toxin expression profiles observed in the current study. Overall, specialised tentacular structures serve unique ecological roles and, in order to fulfil their functions, they possess distinct venom cocktails.

Characterising Functional Venom Profiles of Anthozoans and Medusozoans within Their Ecological Context.

This review examines the current state of knowledge regarding toxins from anthozoans (sea anemones, coral, zoanthids, corallimorphs, sea pens and tube anemones). We provide an overview of venom from phylum Cnidaria and review the diversity of venom composition between the two major clades (Medusozoa and Anthozoa). We highlight that the functional and ecological context of venom has implications for the temporal and spatial expression of protein and peptide toxins within class Anthozoa. Understanding the nuances in the regulation of venom arsenals has been made possible by recent advances in analytical technologies that allow characterisation of the spatial distributions of toxins. Furthermore, anthozoans are unique in that ecological roles can be assigned using tissue expression data, thereby circumventing some of the challenges related to pharmacological screening.