Barrel-stave model or toroidal model? A case study on melittin pores

Area of Science:

• Biophysics
• Membrane Biology
• Peptide Science

Background:

• Amphiphilic peptides like melittin can induce transmembrane pores.
• These pores are often modeled using the barrel-stave model, exemplified by alamethicin.
• The structural basis of melittin-induced pores requires further investigation.

Purpose of the Study:

• To investigate the structural model of transmembrane pores induced by melittin.
• To compare melittin pore formation with other peptides like alamethicin and magainin.
• To determine if melittin pores conform to the barrel-stave or toroidal model.

Main Methods:

• Oriented circular dichroism (OCD) to determine melittin helix orientation relative to lipid bilayers.
• Neutron scattering to detect and characterize transmembrane pores.
• Systematic measurement of OCD spectra under varying physical conditions and lipid compositions.

Main Results:

• Melittin helix orientation is dependent on lipid bilayer conditions, adopting either perpendicular or parallel alignments.
• Transmembrane pore formation was observed exclusively when melittin helices were oriented perpendicularly.
• Melittin pore properties closely resemble those of magainin pores, not alamethicin pores.

Conclusions:

• Melittin-induced transmembrane pores do not follow the barrel-stave model.
• Melittin, magainin, and protegrins induce pores consistent with the toroidal model.
• Only alamethicin among the investigated natural peptides conforms to the barrel-stave pore model.