Melittin induced voltage-dependent conductance in DOPC lipid bilayers

Area of Science:

• Biophysics
• Membrane Biophysics
• Ion Channel Formation

Background:

• Melittin is a peptide toxin known to interact with lipid membranes.
• Understanding melittin's interaction with lipid bilayers is crucial for its toxicological and potential therapeutic applications.
• The precise mechanism of melittin-induced membrane permeabilization remains under investigation.

Purpose of the Study:

• To investigate the electrical properties of melittin-induced conductance in dioleoylphosphatidylcholine planar bilayers.
• To characterize the voltage and concentration dependence of melittin-induced ion transport.
• To explore the kinetics and pH-dependence of melittin pore formation.

Main Methods:

• Planar lipid bilayer electrophysiology using dioleoylphosphatidylcholine.
• Voltage-clamp measurements to determine current-voltage (I-V) characteristics.
• Systematic variation of voltage, peptide concentration, salt concentration, and pH.

Main Results:

• Melittin induced voltage-dependent conductance that increased exponentially with applied voltage.
• Conductance was proportional to the fourth power of melittin concentration and influenced by salt concentration.
• Discrete conductance steps were observed, with variable amplitudes.
• Asymmetric conductance was initially observed, becoming symmetric over time.
• Slower current stabilization at pH 7 compared to pH 8 suggested pH-dependent prepore formation involving melittin's N-terminus.

Conclusions:

• Melittin forms voltage-gated ion-conducting pathways in lipid bilayers.
• The pore formation process is concentration-dependent and exhibits distinct kinetic phases.
• The N-terminus of melittin plays a role in the slow formation of a prepore intermediate, influenced by pH.