Sea Anemone Actinoporins: The Transition from a Folded Soluble State to a Functionally Active Membrane-Bound Oligomeric Pore

Title: Sea Anemone Actinoporins: The Transition from a Folded Soluble State to a Functionally Active Membrane-Bound Oligomeric Pore

Volume: 8 Issue: 6

Author(s): J. Alegre-Cebollada, M. Onaderra, J. G. Gavilanes and A. Martinez del Pozo

Affiliation:

Keywords: Actinoporins, equinatoxin, sticholysin, pore-forming toxin, lipid-protein interaction, membrane, pore, oligomerization

Abstract: Actinoporins are a family of 20-kDa, basic proteins isolated from sea anemones, whose activity is inhibited by preincubation with sphingomyelin. They are produced in monomeric soluble form but, when binding to the plasma membrane, they oligomerize to produce functional pores which result in cell lysis. Equinatoxin II (EqtII) from Actinia equina and Sticholysin II (StnII) from Stichodactyla helianthus are the actinoporins that have been studied in more detail. Both proteins display a β-sandwich fold composed of 10 β-strands flanked on each side by two short α-helices. Twodimensional crystallization on lipid monolayers has allowed the determination of low-resolution models of tetrameric structures distinct from the pore. However, the actual structure of the pore is not known yet. Wild-type EqtII and StnII, as well as a nice collection of natural and artificially made variants of both proteins, have been produced in Escherichia coli and purified. Their characterization has allowed the proposal of a model for the mechanism of pore formation. Four regions of the actinoporins structure seem to play an important role. First, a phosphocholine-binding site and a cluster of exposed aromatic residues, together with a basic region, would be involved in the initial interaction with the membrane, whereas the amphipathic N-terminal region would be essential for oligomerization and pore formation. Accordingly, the model states that pore formation would proceed in at least four steps: Monomer binding to the membrane interface, assembly of four monomers, and at least two distinct conformational changes driving to the final formation of the functional pore.

Cite this article as:

Alegre-Cebollada J., Onaderra M., Gavilanes G. J. and del Pozo Martinez A., Sea Anemone Actinoporins: The Transition from a Folded Soluble State to a Functionally Active Membrane-Bound Oligomeric Pore, Current Protein & Peptide Science 2007; 8 (6) . https://dx.doi.org/10.2174/138920307783018686

DOI https://dx.doi.org/10.2174/138920307783018686	Print ISSN 1389-2037
Publisher Name Bentham Science Publisher	Online ISSN 1875-5550