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An EPR study of ampullosporin A, a medium-length peptaibiotic, in bicelles and vesicles
Marco Bortolus1, Annalisa Dalzini2, Fernando Formaggio2
1Dipartimento di Scienze Chimiche, Università degli Studi di Padova, 35131 Padova, Italy. marina.gobbo@unipd.it annalisa.maniero@unipd.it and Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, 20126, Milano, Italy.
Abstract:
Ampullosporin A is a medium-length (14-amino acid long) hydrophobic peptide of the peptaibol family. In this work, electron paramagnetic resonance and circular dichroism spectroscopies were applied to study the interaction of synthetic ampullosporin A and three spin-labeled analogs with small unilamellar vesicles and bicelles. Zwitterionic vesicles were used to investigate the conformation and the penetration depth of the peptide at room temperature. Bicelles were employed in combination with EPR spectroscopy to study the order, dynamics, orientation, aggregation and the 3D-structure of the peptide at near physiological temperature. In the membrane, the peptide adopts a helical structure that changes in nature depending on the thickness of the membrane-mimetic system, from mostly α-helical in vesicles to a more elongated helix in bicelles, suggesting an increase in the 310-helical content. The orientation assumed by the peptide also shows a dependence on the membrane-mimetic system: in bicelles, ampullosporin A has a transmembrane orientation at a peptide-to-lipid (P : L) ratio of 1 : 100 and higher, while in vesicles it undergoes a transition from a parallel to a transmembrane orientation as a function of the P : L ratio. In bicelles, the peptide was found to be monomeric at a P : L ratio of 1 : 25 and lower. Overall, the comparison of the results obtained in the two membrane-mimetic systems showed that ampullosporin A has a rather flexible structure that readily adapts to the bilayer thickness.
Insights
Ampullosporin A, a peptaibol peptide, exhibits a flexible helical structure that adapts to membrane thickness. Its orientation and aggregation depend on the membrane environment and peptide-to-lipid ratio.
Area of Science:
- Biophysics
- Structural Biology
- Membrane Biophysics
Background:
- Ampullosporin A is a 14-amino acid hydrophobic peptide belonging to the peptaibol family.
- Understanding peptide-membrane interactions is crucial for elucidating their biological functions.
Purpose of the Study:
- To investigate the conformational changes, orientation, and aggregation of Ampullosporin A within membrane-mimetic systems.
- To determine how membrane thickness and peptide-to-lipid ratio influence Ampullosporin A's behavior.
Main Methods:
- Electron paramagnetic resonance (EPR) spectroscopy and circular dichroism (CD) spectroscopy were employed.
- Synthetic Ampullosporin A and spin-labeled analogs were studied using small unilamellar vesicles (SUVs) and bicelles.
- Experiments were conducted at room temperature and near physiological temperatures.
Main Results:
- Ampullosporin A adopts a helical structure, primarily alpha-helical in vesicles and a more elongated helix with increased 310-helical content in bicelles.
- Peptide orientation varies with membrane system: transmembrane in bicelles (at higher peptide-to-lipid ratios) and transitioning from parallel to transmembrane in vesicles.
- Ampullosporin A exists as a monomer in bicelles at lower peptide-to-lipid ratios (1:25 and below).
Conclusions:
- Ampullosporin A demonstrates structural flexibility, adapting its helical conformation and orientation to the surrounding bilayer thickness.
- The study highlights the distinct behaviors of Ampullosporin A in different membrane environments, influenced by lipid composition and concentration.
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