Asymmetric dimethylarginine is transported by the mitochondrial carrier SLC25A2

Area of Science:

• Mitochondrial biology
• Amino acid transport
• Molecular genetics

Background:

• Asymmetric dimethyl L-arginine (ADMA) is produced during protein degradation within cells and mitochondria.
• The precise mechanisms for ADMA transport across the inner mitochondrial membrane are not fully understood.
• Identifying ADMA transporters is crucial for understanding its cellular roles and metabolic regulation.

Purpose of the Study:

• To identify the specific carrier protein responsible for transporting ADMA across the inner mitochondrial membrane.
• To characterize the transport properties and specificity of the identified carrier for ADMA.

Main Methods:

• Recombinant expression and purification of the mitochondrial solute carrier SLC25A2.
• Reconstitution of purified SLC25A2 into liposomes to study transport kinetics.
• Assays to measure unidirectional transport and exchange of ADMA against other amino acids.
• Inhibition studies using ADMA and symmetric dimethylarginine (SDMA) to assess specificity.

Main Results:

• SLC25A2 efficiently transports ADMA across the liposomal membrane in both directions.
• SLC25A2 also transports known substrates arginine, lysine, and ornithine, but not SDMA.
• ADMA transport by SLC25A2 follows first-order kinetics and is highly specific.
• ADMA competitively inhibits SLC25A2 activity with a low inhibition constant.

Conclusions:

• SLC25A2 is identified as a key transporter of ADMA across the inner mitochondrial membrane.
• SLC25A2 likely plays a significant role in exporting ADMA from mitochondria, particularly when the AGXT2 enzyme is absent.
• SLC25A2 may also mediate ADMA import into mitochondria for metabolism by AGXT2 in specific cell types.