Abstract
Actinoporins are proteinaceous toxins known for their ability to bind to and create pores in cellular membranes. This quality has generated interest in their potential use as new tools, such as therapeutic immunotoxins. Isolated historically from sea anemones, genes encoding for similar actinoporin-like proteins have since been found in a small number of other animal phyla. Sequencing and de novo assembly of Irish Haliclona transcriptomes indicated that sponges also possess similar genes. An exhaustive analysis of publicly available sequencing data from other sponges showed that this is a potentially widespread feature of the Porifera. While many sponge proteins possess a sequence similarity of 27.70–59.06% to actinoporins, they show consistency in predicted structure. One gene copy from H. indistincta has significant sequence similarity to sea anemone actinoporins and possesses conserved residues associated with the fundamental roles of sphingomyelin recognition, membrane attachment, oligomerization, and pore formation, indicating that it may be an actinoporin. Phylogenetic analyses indicate frequent gene duplication, no distinct clade for sponge-derived proteins, and a stronger signal towards actinoporins than similar proteins from other phyla. Overall, this study provides evidence that a diverse array of Porifera represents a novel source of actinoporin-like proteins which may have biotechnological and pharmaceutical applications.
Highlights
Actinoporins (APs) are proteinaceous α-pore-forming toxins originally isolated from and named after sea anemones [1]
Approximately 472.68, 69.80, 257.97, 207.46, and 94.64 Mbp of data were acquired for H. cinerea, H. indistincta, H. oculata, H. simulans, and H. viscosa, respectively
More data were available for H. cinerea, H. oculata, and H. simulans, which appeared to be reflected in the generally larger assembly size and higher number of true genes when compared to H. indistincta and H. viscosa
Summary
Actinoporins (APs) are proteinaceous α-pore-forming toxins originally isolated from and named after sea anemones [1]. This group of toxins typically exhibit several common characteristics, such as a common absence of cysteine residues, a high isoelectric point (>8.8), and a small size (~20 kDa) [2]. After binding to a target membrane, APs undergo a conformational change in which the N-terminal region, containing one of the α-helices, is translocated to lie flat upon the membrane surface [8,9]. The qualities of APs which allow for their membrane-binding and pore-forming activity have attracted attention regarding potential biotechnological and therapeutic applications, such as the design of immunotoxins, nanopores, adjuvants, and SM-specific probes [16,17,18,19]
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