Lasalocid Acid Antibiotic at a Membrane Surface Probed by Sum Frequency Generation Spectroscopy

Area of Science:

• Biochemistry
• Biophysics
• Membrane Biophysics

Background:

• Carboxyl polyether ionophores (CPIs) are vital veterinary antibiotics and growth promoters in ruminants.
• CPIs show potential against drug-resistant bacteria, but their mechanism of action requires elucidation.
• Understanding ionophore-membrane interactions is key to developing safer, more effective therapeutic agents.

Purpose of the Study:

• To investigate the initial interaction of the carboxyl polyether ionophore lasalocid acid (LA) with model lipid membranes.
• To determine if free ionophore adsorption to the membrane surface precedes cation interaction for ion transport.

Main Methods:

• Sum-frequency generation (SFG) vibrational spectroscopy to probe molecular structure and orientation at the membrane interface.
• Surface tensiometry to measure changes in surface pressure and assess self-assembly and membrane disruption.

Main Results:

• Surface tensiometry revealed that free lasalocid acid undergoes self-assembly with lipid monolayers.
• SFG spectroscopy indicated partial insertion of lasalocid acid into the lipid monolayer.
• Subsequent complexation with sodium chloride led to disruption of the lipid monolayer structure.

Conclusions:

• The study strongly suggests that the initial adsorption and self-assembly of the free ionophore on the membrane surface is a critical prerequisite for ion transport.
• Complexation with metal ions, specifically sodium chloride in this case, appears to be the key step enabling the ionophore to traverse the lipid membrane.
• These findings provide crucial insights into the mode-of-action of carboxyl polyether ionophores, informing the development of novel therapeutic agents.