The mitochondrial carnitine/acylcarnitine carrier: function, structure and physiopathology

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• The carnitine/acylcarnitine carrier (CAC) is a crucial inner mitochondrial membrane transporter.
• It belongs to the mitochondrial carrier protein family and facilitates the transport of carnitine and acylcarnitines.
• Functional studies often utilize purified proteins from rat liver or recombinant sources reconstituted into liposomes.

Purpose of the Study:

• To elucidate the function and significance of the carnitine/acylcarnitine carrier (CAC) in cellular metabolism.
• To highlight the role of CAC in fatty acid transport and energy production.
• To describe the clinical implications of CAC gene mutations, specifically carnitine carrier deficiency.

Main Methods:

• Functional characterization of the carnitine/acylcarnitine carrier (CAC) using purified proteins and liposome reconstitution.
• Analysis of the human SLC25A20 gene coding for CAC.
• Biochemical and genetic testing for diagnosis of carnitine carrier deficiency.

Main Results:

• The mammalian CAC exhibits higher affinity for longer acyl chain acylcarnitines.
• CAC catalyzes the exchange of intramitochondrial free carnitine for cytosolic acylcarnitines, enabling fatty acyl unit transport into the mitochondrial matrix.
• Mutations in the human SLC25A20 gene lead to carnitine carrier deficiency, a severe autosomal recessive disorder.
• 35 distinct mutations in the CAC gene have been identified in patients, with some missense mutations affecting conserved residues.

Conclusions:

• The carnitine/acylcarnitine carrier (CAC) is essential for cellular energy metabolism through fatty acid transport.
• Carnitine carrier deficiency, caused by SLC25A20 gene mutations, results in severe metabolic disturbances.
• Diagnosis relies on biochemical and genetic tests, with dietary management as the primary treatment; novel pharmacological approaches are emerging for milder cases.