The sea anemone actinoporin (Arg‐Gly‐Asp) conserved motif is involved in maintaining the competent oligomerization state of these pore‐forming toxins

<jats:sec><jats:label/><jats:p>Sea anemone actinoporins constitute an optimum model to investigate mechanisms of membrane pore formation. All actinoporins of known structure show a general fold of a β‐sandwich motif flanked by two α‐helices. The crucial structure for pore formation seems to be the helix located at the N‐terminal end. The role of several other protein regions in membrane attachment is also well established. However, not much is known about the protein residues involved in the oligomerization required for pore formation. Previous detailed analysis of the soluble three‐dimensional structures of different wild‐type and mutant actinoporins from <jats:italic>Stychodactyla helianthus</jats:italic> suggested residues which could be involved in this oligomerization. One of these stretches contains a conserved sequence compatible with an integrin‐binding <jats:styled-content style="fixed-case">RGD</jats:styled-content> motif. The results presented now deal with mutants affecting this motif in the well‐characterized actinoporin sticholysin <jats:styled-content style="fixed-case">II</jats:styled-content>. Small modifications along this three‐residue sequence had profound effects on its solubility. Just a single methyl group yielded an <jats:styled-content style="fixed-case">RAD</jats:styled-content> mutant version with a highly diminished haemolytic activity and altered oligomerization behaviour. The results obtained are discussed in terms of a key role for the <jats:styled-content style="fixed-case">RGD</jats:styled-content> motif in maintaining the actinoporins' pore‐competent state of protein oligomerization.</jats:p></jats:sec><jats:sec><jats:title>Structured digital abstract</jats:title><jats:p><jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.uniprot.org/uniprot/P07845">StnII</jats:ext-link> and <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.uniprot.org/uniprot/P07845">StnII</jats:ext-link> <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0407">bind</jats:ext-link> by <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0071">molecular sieving</jats:ext-link> (<jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.ebi.ac.uk/intact/interaction/EBI-9084000">1</jats:ext-link>, <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.ebi.ac.uk/intact/interaction/EBI-9084034">2</jats:ext-link>)</jats:p></jats:sec>