Structure of the alamethicin pore reconstructed by x-ray diffraction analysis

Area of Science:

• Structural biology
• Biophysics
• Membrane protein structure

Background:

• Alameticin forms transmembrane pores in lipid bilayers.
• Understanding pore structure is crucial for elucidating its function and antibacterial activity.

Purpose of the Study:

• To reconstruct the electron density profile of the alamethicin-induced transmembrane pore.
• To determine the precise structural arrangement of alamethicin within the lipid bilayer.

Main Methods:

• X-ray diffraction on fully hydrated and dehydrated multiple bilayers of alamethicin-lipid mixtures.
• Multiwavelength anomalous diffraction (MAD) using a brominated lipid at the bromine K edge.
• Correlation with neutron in-plane scattering and oriented circular dichroism.

Main Results:

• Dehydrated conditions induced long-range correlation and rhombohedral symmetry in membrane pores.
• X-ray diffraction unambiguously revealed an 8-helix barrel-stave alamethicin pore structure.
• This structure aligns with stable pores observed in hydrated bilayers at high peptide/lipid ratios.

Conclusions:

• The alamethicin pore is a barrel-stave structure composed of eight alamethicin helices.
• This structure is consistent with stable pore formation and the antibacterial activity of alamethicin.
• X-ray diffraction, particularly MAD, is a powerful tool for resolving membrane protein structures.