title: Functional and topological studies with Trp-containing analogs of the peptide StII(1-30) derived from the N-terminus of the pore forming toxin sticholysin II: contribution to understand its orientation in membrane.
abstract: Sticholysin II (St II) is the most potent cytolysin produced by the sea anemone Stichodactyla helianthus, exerting hemolytic activity via pore formation in membranes. The toxin's N-terminus contains an amphipathic α-helix that is very likely involved in pore formation. We have previously demonstrated that the synthetic peptide StII(1-30) encompassing the 1-30 segment of St II forms pores of similar radius to that of the protein (around 1 nm), being a good model of toxin functionality. Here we have studied the functional and conformational properties of fluorescent analogs of StII(1-30) in lipid membranes. The analogs were obtained by replacing Leu residues at positions 2, 12, 17, and 24 with the intrinsically fluorescent amino acid Trp (StII(1-30L2W), StII(1-30L12W), StII(1-30L17W), or StII(1-30L24W), respectively). The exchange by Trp did not significantly modify the activity and conformation of the parent peptide. The blue-shift and intensity enhancement of fluorescence in the presence of membrane indicated that Trp at position 2 is more deeply buried in the hydrophobic region of the bilayer. These experiments, as well as assays with water-soluble or spin-labeled lipid-soluble fluorescence quenchers suggest an orientation of StII(1-30) with its N-terminus oriented towards the hydrophobic core of the bilayer while the rest of the peptide is more exposed to the aqueous environment, as hypothesized for sticholysins.
authors.affiliation: Center for Protein Studies, Biology Faculty, University of Havana (UH), Havana, Cuba.
authors.forename: Uris
authors.initials: U
authors.lastname: Ros
authors.forename: Ana Lucia C F
authors.initials: AL
authors.lastname: Souto
authors.forename: Felipe J
authors.initials: FJ
authors.lastname: de Oliveira
authors.forename: Edson
authors.initials: E
authors.lastname: Crusca
authors.forename: Fabiola
authors.initials: F
authors.lastname: Pazos
authors.forename: Eduardo M
authors.initials: EM
authors.lastname: Cilli
authors.forename: Maria E
authors.initials: ME
authors.lastname: Lanio
authors.forename: Shirley
authors.initials: S
authors.lastname: Schreier
authors.forename: Carlos
authors.initials: C
authors.lastname: Alvarez
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D008563:Membrane Lipids; D008969:Molecular Sequence Data; D009930:Organic Chemicals; D010455:Peptides / Q000737:chemistry; D017433:Protein Structure, Secondary; D012615:Sea Anemones
chemical_list: D008563:Membrane Lipids; D009930:Organic Chemicals; D010455:Peptides
keywords: Trp-containing peptides; fluorescence; pore-forming toxin; sticholysin; transbilayer orientation