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MOTS-c and SS-31 are the two peptides most often discussed in mitochondrial research, and they are often mentioned in the same breath. They are very different molecules, though. One is a signalling peptide the mitochondrion makes itself, the other is a synthetic tetrapeptide designed to sit in the mitochondrial membrane. This page compares what the published literature examines, for research reference purposes only.
MOTS-c is studied as a signal: a peptide encoded in mitochondrial DNA that can act on pathways elsewhere in the cell. SS-31 is studied as a structural tool: a small peptide that concentrates at the inner mitochondrial membrane and associates with cardiolipin. If MOTS-c is about what mitochondria tell the cell, SS-31 is about the membrane mitochondria are built from.
MOTS-c was described in 2015 by Lee and colleagues in Cell Metabolism. It is a 16 amino acid peptide encoded within the 12S rRNA region of mitochondrial DNA, which places it among the mitochondrial-derived peptides. Later work by Kim and colleagues (Cell Metabolism, 2018) reported that it can move to the nucleus under metabolic stress in cell models.
SS-31 comes from the Szeto-Schiller family of synthetic peptides, developed by Hazel Szeto and Peter Schiller. It is a tetrapeptide, D-Arg-Dmt-Lys-Phe-NH2, where Dmt is 2',6'-dimethyltyrosine. Its alternating aromatic and basic residues are what the literature links to its uptake into mitochondria. It is also known in the literature as elamipretide.
| Feature | MOTS-c | SS-31 |
|---|---|---|
| Origin | Encoded in mitochondrial DNA (12S rRNA region) | Synthetic Szeto-Schiller peptide |
| Length | 16 amino acids | 4 amino acids |
| Main research focus | Metabolic signalling, AMPK-related pathways | Inner mitochondrial membrane, cardiolipin |
| Where it acts in models | Cytoplasm and, under stress, the nucleus | Inner mitochondrial membrane |
| Key early publication | Lee et al., Cell Metabolism, 2015 | Szeto, British Journal of Pharmacology, 2014 (review) |
Research on MOTS-c focuses on signalling. Cell and animal studies have examined its effects on the folate cycle, AMPK activation and gene expression linked to metabolic stress responses. Because it is encoded in mitochondrial DNA, it is also studied as evidence that mitochondria communicate with the rest of the cell through peptides.
Research on SS-31 focuses on structure. Studies such as Birk and colleagues (Journal of the American Society of Nephrology, 2013) examined its interaction with cardiolipin, a phospholipid found almost only in the inner mitochondrial membrane, and how that relates to cristae structure and electron transport in laboratory models. SS-31 has also been through clinical research programmes run by its developer, which are outside the scope of this page.
The two peptides answer different research questions, which is why they are often studied side by side rather than as alternatives. Comparing a signalling peptide with a membrane-targeted one can help separate effects that start with mitochondrial communication from effects that start with mitochondrial structure.
Both are listed as research reference materials: MOTS-c and SS-31, and together in the Mitochondrial Pair. For more on each, see MOTS-c and the mitochondrial-derived peptides and SS-31 and cardiolipin research.
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