Acylcarnitines at the Membrane Surface: Insertion Parameters for a Mitochondrial Leaflet Model

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Physiology

Background:

• Elevated acylcarnitines (ACs) are linked to metabolic disorders like obesity and insulin resistance.
• The precise mechanisms by which ACs contribute to these pathophysiological effects are not well understood.
• Investigating AC interactions with mitochondrial membranes is crucial for understanding their role in disease.

Purpose of the Study:

• To elucidate the interaction mechanisms between acylcarnitines and the mitochondrial inner membrane.
• To model the outer leaflet of the mitochondrial inner membrane to study AC insertion.
• To determine the parameters and consequences of AC insertion into the membrane.

Main Methods:

• Utilized Langmuir monolayers and cushioned supported bilayers to model the mitochondrial inner membrane's outer leaflet.
• Employed epifluorescence microscopy to observe AC interactions and leaflet changes.
• Performed constant-pressure insertion assays to quantify AC insertion parameters.

Main Results:

• Observed local leaflet expansion upon exposure to long-chain ACs, indicating insertion.
• Determined that AC insertion involves primarily the acyl chain (21 ± 3 Ų), leaving the carnitine moiety exposed.
• Found the carnitine moiety requires a larger area (37 ± 3 Ų) and likely alters surface electrostatics.

Conclusions:

• Acylcarnitine insertion into mitochondrial membranes occurs primarily via the acyl chain.
• This insertion alters membrane morphology and surface electrostatics, particularly with long-chain ACs.
• ACs may trigger signaling pathways in the inner mitochondrial membrane, contributing to pathophysiological outcomes.