Family

Sea anemone actinoporin-like (IPR009104)

Short name: Anemon_actinoporin-like

Family relationships

None.

Description

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 [PMID: 11689232]. 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), sticholysins (from Stichodactyla helianthus), magnificalysins (from Heteractis magnifica), and tenebrosins (from Actinia tenebrosa), which exhibit pore-forming, haemolytic, cytotoxic, and heart stimulatory activities.

Cytolysins adopt a stable soluble structure, which undergoes a conformational change when brought in contact with a membrane, leading to an active, membrane-bound form that inserts spontaneously into the membrane. They often oligomerise on the membrane surface, before puncturing the lipid bilayers, causing the cell to lyse. The 20kDa sea anemone cytolysins require a phosphocholine lipid headgroup for binding, however sphingomyelin is required for the toxin to promote membrane permeability [PMID: 14604518]. The crystal structures of equinotoxin II [PMID: 11827489] and sticholysin II [PMID: 14604522] 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.

Interestingly, this entry also includes bryoporin from the moss Physcomitrella patens. It shares the protein structure similarity with sea anemone actinoporin. The bryoporin gene was upregulated by various abiotic stresses, in particular most strongly by dehydration stress. Overexpression of the bryoporin gene heightens drought tolerance in P. patens significantly [PMID: 19674339].

GO terms

Biological Process

GO:0006812 cation transport
GO:0052331 hemolysis in other organism involved in symbiotic interaction
GO:0046931 pore complex assembly

Molecular Function

GO:0015267 channel activity

Cellular Component

GO:0046930 pore complex

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
Pfam