Model ion channels: gramicidin and alamethicin

Area of Science:

• Biophysics
• Structural Biology
• Molecular Biology

Background:

• Gramicidin and alamethicin are peptides known to form ion channels.
• Understanding their conformational and dynamic properties is key to elucidating ion channel activity at a molecular level.
• Previous studies have identified multiple gramicidin isomers in solution and proposed a helical structure in membranes.

Purpose of the Study:

• To investigate the conformational heterogeneity and dynamic properties of gramicidin and alamethicin.
• To understand the molecular basis of ion channel formation and function.
• To explore the role of peptide conformation and dynamics in ion transport and channel behavior.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy (solution-state and solid-state)
• X-ray crystallography
• Circular Dichroism (CD) spectroscopy
• Fluorescence spectroscopy
• Computational simulations

Main Results:

• Gramicidin exhibits conformational heterogeneity in solution, with at least five major isomers identified.
• In lipid membranes, gramicidin adopts a right-handed beta 6.3 helical conformation, with two helices likely forming the conducting channel.
• Side-chain conformations influence ion conductance and selectivity by altering the electrostatic environment.
• Peptide dynamics (backbone and side-chain) are critical for ion transport.
• Gramicidin monomers exhibit rotational and translational motion within the membrane, affecting channel lifetime and stability.

Conclusions:

• Experimental and computational studies are progressively detailing gramicidin's membrane-bound conformation and dynamics.
• Understanding these properties is crucial for advancing computational simulations of ion transport.
• Gramicidin-membrane interactions influence channel subconductance states, flickering, and overall conformational stability.
• The molecular origin of voltage-dependent conductance in alamethicin channels remains a significant biophysical problem.