title: Differences in activity of actinoporins are related with the hydrophobicity of their N-terminus.
abstract: Actinoporins are pore-forming toxins (PFT) produced by sea anemones with molecular mass around 20 kDa and high affinity for sphingomyelin. The most studied atinoporins are sticholysins I and II (StI/StII) from Stichodactyla helianthus, equinatoxin II (EqtII) from Actinia equina, and fragaceatoxin C (FraC) from Actinia fragacea. Their N-terminal sequences encompassing residues 1-30 seem to be the best candidates for pore formation. This segment comprises an amphipathic α-helix preceded by a more or less hydrophobic segment, depending on the toxin, of around 10 amino acid residues. Although it is clear that the N-terminal is the most variable sequence in this protein family, the role of their hydrophobic segment in not fully understood. Here we show a comparison of StI, StII, EqtII, and FraC activities with that of their respective N-terminal synthetic peptides. The hemolytic and permeabilizing activity of the peptides reproduce qualitatively the behavior of their respective parental proteins and are particularly related to the hydrophobicity of the corresponding 1-10 segment. Furthermore, the dendrogram analysis of actinoporins' N-terminal sequence allows relating differences in alignment with differences in activity among the four toxins. We have also evaluated the penetration depth of the N-terminal segment of StI and StII by using Trp-containing peptide-analogs. Our data suggest that the N-terminus of StII is more deeply buried into the hydrophobic core of the bilayer than that of StI. We hypothesize that the highest activity of StII could be ascribed to a larger hydrophobic continuum, an uninterrupted sequence of non-charged mainly hydrophobic amino acid residues, of its N-terminus promoting a highest ability to partially insert in the membrane core. Moreover, as we show for four related peptides that a higher hydrophobicity contributes to increase the activity, we reinforce the notion that this property must be taken into account to design new potent membranotropic agents.
authors.affiliation: Center for Protein Studies, Biology Faculty, University of Havana, Havana, Cuba.
authors.forename: Uris
authors.initials: U
authors.lastname: Ros
authors.affiliation: Center for Protein Studies, Biology Faculty, University of Havana, Havana, Cuba.
authors.forename: Wendy
authors.initials: W
authors.lastname: Rodríguez-Vera
authors.affiliation: Center for Protein Studies, Biology Faculty, University of Havana, Havana, Cuba.
authors.forename: Lohans
authors.initials: L
authors.lastname: Pedrera
authors.affiliation: Center for Protein Studies, Biology Faculty, University of Havana, Havana, Cuba.
authors.forename: Pedro A
authors.initials: PA
authors.lastname: Valiente
authors.affiliation: Center for Protein Studies, Biology Faculty, University of Havana, Havana, Cuba.
authors.forename: Sheila
authors.initials: S
authors.lastname: Cabezas
authors.affiliation: Center for Protein Studies, Biology Faculty, University of Havana, Havana, Cuba.
authors.forename: María E
authors.initials: ME
authors.lastname: Lanio
authors.affiliation: Max Planck Institute for Intelligent Systems, Stuttgart, Germany and German Cancer Research Center, Bioquant, Heidelberg, Germany; Interfaculty Institute of Biochemistry, University of Tubingen, Tubingen, Germany.
authors.forename: Ana J
authors.initials: AJ
authors.lastname: García-Sáez
authors.affiliation: Center for Protein Studies, Biology Faculty, University of Havana, Havana, Cuba. Electronic address: calvarez@fbio.uh.cu.
authors.forename: Carlos
authors.initials: C
authors.lastname: Alvarez
mesh_terms: D000595:Amino Acid Sequence; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008969:Molecular Sequence Data; D010455:Peptides / Q000009:adverse effects / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D010455:Peptides
keywords: Actinoporin; Hemolytic activity; Peptide–membrane interaction; Permeabilizing activity; Pore-forming toxins