Actinoporins: From the Structure and Function to the Generation of Biotechnological and Therapeutic Tools

Abstract

Actinoporins (APs) are a family of pore-forming toxins (PFTs) from sea anemones. These biomolecules exhibit the ability to exist as soluble monomers within an aqueous medium or as constitutively open oligomers in biological membranes. Through their conformational plasticity, actinoporins are considered good candidate molecules to be included for the rational design of molecular tools, such as immunotoxins directed against tumor cells and stochastic biosensors based on nanopores to analyze unique DNA or protein molecules. Additionally, the ability of these proteins to bind to sphingomyelin (SM) facilitates their use for the design of molecular probes to identify SM in the cells. The immunomodulatory activity of actinoporins in liposomal formulations for vaccine development has also been evaluated. In this review, we describe the potential of actinoporins for use in the development of molecular tools that could be used for possible medical and biotechnological applications.

Current Perspective on the Membrane-Damaging Action of Thermostable Direct Hemolysin, an Atypical Bacterial Pore-forming Toxin

“…Based on the structural similarity, TDH finds its nearest neighbours in the actinoporin family of eukaryotic PFTs that include Equinatoxin II, Fragaceatoxin C and Sticholysin II (Yanagihara et al, 2010;Caaveiro and Tsumoto, 2021). The actinoporins constitute a unique family of eukaryotic ⍺-PFTs secreted by the sea anemones (Ramírez-Carreto et al, 2020). As observed with TDH, actinoporins are also generally produced as water-soluble, single domain protein with a β-sandwich core architecture (Rojko et al, 2016).…”

“…As a result, Cys151-Cys161 disulphide linkage acts to hold this C-terminal extension against the core β-sandwich domain (Kundu et al, 2017). Interestingly, actinoporins are generally cysteine-less proteins (Ramírez-Carreto et al, 2020). Moreover, they do not possess the extended C-terminal region that is present in TDH (Kundu et al, 2017).…”

“…Some of the PFTs display direct interactions with membrane lipid components. For example, actinoporin family of PFTs, that are structurally similar to TDH, display ability to recognise and bind to the phosphocholine moiety of phosphatidylcholine and/ or sphingomyelin (Cosentino et al, 2016;Ramírez-Carreto et al, 2020). Moreover, actinoporin structures harbour distinct binding site(s)/pocket(s) involving conserved set of residues for lipid binding (Rojko et al, 2016).…”

PMP2/FABP8 induces PI(4,5)P2-dependent transbilayer reorganization of sphingomyelin in the plasma membrane

“…To understand the organization and dynamics of local SM-rich domains, several approaches to visualize them with fluorescent SM analogs or SM-binding probes have been reported (Hong et al, 2002;Honigmann et al, 2014;Kinoshita et al, 2017;Kiyokawa et al, 2005;Kol et al, 2019). In particular, specific SMbinding proteins have attracted a lot of attention because they can be easily used to label endogenous SM-rich domains in cell membranes, with few artifacts (Kobayashi and Menon, 2018;Ramı ´rez-Carreto et al, 2020). We developed methods for visualizing clusters of SM in vivo using lysenin, a specific SM-binding protein originally isolated from the coelomic fluid of the earthworm Eisenia fetida (Abe and Kobayashi, 2014;Abe et al, 2012;Makino et al, 2015).…”

Functional and Structural Variation among Sticholysins, Pore-Forming Proteins from the Sea Anemone Stichodactyla helianthus

“…On one hand, they are one of the main components of sea anemones venom. Venoms are a source of valuable information from a biochemical point of view, both for the possible fabrication of antidotes (for the most dangerous species) and the potential use of their components to our benefit [ 185 ], such as designing immunotoxins [ 186 , 187 , 188 , 189 , 190 ], sequencing DNA [ 191 ], facilitating drugs cell penetration [ 192 ] or constructing specific SM sensors [ 193 , 194 , 195 ]. Furthermore, actinoporins are unique since they can remain stably folded in solution until they encounter a membrane with the adequate composition.…”