title: Dynamics and conformational studies of TOAC spin labeled analogues of Ctx(Ile(21))-Ha peptide from Hypsiboas albopunctatus.
abstract: Antimicrobial peptides (AMPs) isolated from several organisms have been receiving much attention due to some specific features that allow them to interact with, bind to, and disrupt cell membranes. The aim of this paper was to study the interactions between a membrane mimetic and the cationic AMP Ctx(Ile(21))-Ha as well as analogues containing the paramagnetic amino acid 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) incorporated at residue positions n = 0, 2, and 13. Circular dichroism studies showed that the peptides, except for [TOAC(13)]Ctx(Ile(21))-Ha, are unstructured in aqueous solution but acquire different amounts of α-helical secondary structure in the presence of trifluorethanol and lysophosphocholine micelles. Fluorescence experiments indicated that all peptides were able to interact with LPC micelles. In addition, Ctx(Ile(21))-Ha and [TOAC(13)]Ctx(Ile(21))-Ha peptides presented similar water accessibility for the Trp residue located near the N-terminal sequence. Electron spin resonance experiments showed two spectral components for [TOAC(0)]Ctx(Ile(21))-Ha, which are most likely due to two membrane-bound peptide conformations. In contrast, TOAC(2) and TOAC(13) derivatives presented a single spectral component corresponding to a strong immobilization of the probe. Thus, our findings allowed the description of the peptide topology in the membrane mimetic, where the N-terminal region is in dynamic equilibrium between an ordered, membrane-bound conformation and a disordered, mobile conformation; position 2 is most likely situated in the lipid polar head group region, and residue 13 is fully inserted into the hydrophobic core of the membrane.
authors.affiliation: Departamento de Bioquímica e Tecnologia Química, Instituto de Química, UNESP-Univ Estadual Paulista, Araraquara/SP, Brazil.
authors.forename: Eduardo F
authors.initials: EF
authors.lastname: Vicente
authors.forename: Luis Guilherme M
authors.initials: LG
authors.lastname: Basso
authors.forename: Graziely F
authors.initials: GF
authors.lastname: Cespedes
authors.forename: Esteban N
authors.initials: EN
authors.lastname: Lorenzón
authors.forename: Mariana S
authors.initials: MS
authors.lastname: Castro
authors.forename: Maria José S
authors.initials: MJ
authors.lastname: Mendes-Giannini
authors.forename: Antonio José
authors.initials: AJ
authors.lastname: Costa-Filho
authors.forename: Eduardo M
authors.initials: EM
authors.lastname: Cilli
mesh_terms: D000595:Amino Acid Sequence; D029845:Amphibian Proteins / Q000032:analysis / Q000737:chemistry*; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000032:analysis / Q000737:chemistry*; D001001:Anura / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry*; D002942:Circular Dichroism; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D057927:Hydrophobic and Hydrophilic Interactions; D008244:Lysophosphatidylcholines; D008567:Membranes, Artificial; D008823:Micelles; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D013113:Spin Labels; D014270:Trifluoroethanol
chemical_list: D029845:Amphibian Proteins; D023181:Antimicrobial Cationic Peptides; D003497:Cyclic N-Oxides; D008244:Lysophosphatidylcholines; D008567:Membranes, Artificial; D008823:Micelles; D013113:Spin Labels; D014270:Trifluoroethanol; C003959:TEMPO; C037109:2,2,6,6-tetramethylpiperidine-N-oxide-4-amino-4-carboxylic acid