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SLC25A45 is required for mitochondrial uptake of methylated amino acids and de novo carnitine biosynthesis

Marília M. Dias, Martin King, Engy Shokry, Sérgio Lilla, Nikki R. Paul, Peter A. Thomason et al. · 2025 · 10 citationsRead the paper

Methylated amino acids accumulate upon the degradation of methylated proteins and are implicated in diverse metabolic and signaling pathways. Disturbed methylated amino acid homeostasis is associated with cardiovascular disease and renal failure. Mitochondria are core processing hubs in conventional amino acid metabolism, but how they interact with methylated amino acids is unclear. Here, we reveal that the orphan mitochondrial solute carrier 25A45 (SLC25A45) is required for the mitochondrial uptake of methylated amino acids. SLC25A45 binds with dimethylarginine and trimethyllysine but has no affinity for unmethylated arginine and lysine. A non-synonymous mutation of human SLC25A45 (R285C) stabilizes the carrier by limiting its proteolytic degradation and associates with altered methylated amino acids in human plasma. Metabolic tracing of trimethyllysine in cancer cells demonstrates that SLC25A45 drives the biosynthesis of the key amino acid derivative, carnitine. SLC25A45 is therefore an essential mediator of compartmentalized methylated amino acid metabolism.

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SLC25A45 is required for the mitochondrial uptake of methylated amino acids, specifically dimethylarginine and trimethyllysine. — ~56-fold increase in dimethylarginine and ~7-fold increase in trimethyllysine in mitochondria expressing SLC25A45-FLAG vs KO (AsPC-1 cells and FreeStyle 293-F cells)
SLC25A45 drives the de novo biosynthesis of carnitine from trimethyllysine in cells expressing BBOX1. (OVCAR-3 and Kuramochi ovarian cancer cell lines)
The R285C mutation in SLC25A45 stabilizes the protein by preventing its degradation by the m-AAA protease (AFG3L2/SPG7). (AsPC-1 cells)
The R285C mutation is associated with altered levels of trimethyllysine, deoxycarnitine, and dimethylarginine in human plasma. — p-value: 1.9 x 10^-80 for trimethyllysine (6,136 Finnish male participants (METSIM))
SLC25A45 has no affinity for unmethylated arginine or lysine. (Isolated mitochondria uptake assays)

Setup: AsPC-1, OVCAR-3, Kuramochi, and HeLa cell lines; isolated mitochondria; human plasma data from METSIM and GCKD studies.
How: The researchers used CRISPR-Cas9 knockout and exogenous expression of SLC25A45 in various cancer cell lines, combined with LC-MS metabolomics and deuterium-labeled amino acid tracing. They also performed protein-protein interaction studies and GWAS analysis of human plasma metabolomes.
Limitations: Lack of a reliable antibody necessitated reliance on tagged exogenous expression. · Direct quantification of transport activity in proteoliposomes was not performed. · Unclear how the R285C mutation specifically interferes with AFG3L2 proteolysis.

Summarized by Gemma 4 from the open-access full text · 8 Oct 2026. Read it