InterPro domain: IPR015926

This entry represents a beta-sandwich domain consisting of 10 strands in two sheets that is found in anemone pore-forming cytolysin and in fungal fruit body lectin.

Sea anemones are a rich source of lethal pore-forming peptides and proteins, known collectively as cytolysins or actinoporins. There are several different groups of cytolysins based on their structure and function [ 1 ]. This entry represents the most numerous group, the 20kDa highly basic peptides. These cytolysins form cation-selective pores in sphingomyelin-containing membranes. Examples include equinatoxins (from Actinia equina (European sea anemone)), sticholysins (from Stoichactis helianthus (Carribean sea anemone) (Stichodactyla helianthus)), magnificalysins (from Radianthus magnifica (Magnificent sea anemone) (Heteractis magnifica)), and tenebrosins (from Actinia tenebrosa (Australian red waratah sea anemone)), which exhibit pore-forming, haemolytic, cytotoxic, and heart stimulatory activities. The crystal structures of equinotoxin II [ 2 ] and sticholysin II [ 3 ] both revealed a compact beta-sandwich consisting of ten strands in two sheets flanked on each side by two short alpha-helices, which is a similar topology to osmotin. It is believed that the beta sandwich structure attaches to the membrane, while a three-turn alpha helix lying on the surface of the beta sheet may be involved in membrane pore formation, possibly by the penetration of the membrane by the helix.

Fungal fruit body lectins and TF antigen-binding lectins carry a domain with a similar structural fold. Fungal fruit body lectin proteins. Fruit body lectins are thought to have insecticidal activity [ 4 ] and may also function in capturing nematodes [ 5 ]. One member of this family, the lectin XCL from Xerocomus chrysenteron, induces drastic changes in the actin cytoskeleton after sugar binding at the cell surface and internalization, and has potent insecticidal activity. The fold of lectin xcl is not related to any of several lectin folds, but shows significant structural similarity to cytolysins [ 6 ].

1. Cytolytic peptide and protein toxins from sea anemones (Anthozoa: Actiniaria). Toxicon 40, 111-24
2. Solution structure of the eukaryotic pore-forming cytolysin equinatoxin II: implications for pore formation. J. Mol. Biol. 315, 1219-29
3. Crystal and electron microscopy structures of sticholysin II actinoporin reveal insights into the mechanism of membrane pore formation. Structure 11, 1319-28
4. Xerocomus chrysenteron lectin: identification of a new pesticidal protein. Biochim. Biophys. Acta 1621, 292-8
5. Two genes encoding fruit body lectins of Pleurotus cornucopiae: sequence similarity with the lectin of a nematode-trapping fungus. Biosci. Biotechnol. Biochem. 66, 2083-9
6. A new lectin family with structure similarity to actinoporins revealed by the crystal structure of Xerocomus chrysenteron lectin XCL. J. Mol. Biol. 344, 1409-20