MOTS-c

MOTS-c is a sixteen amino acid peptide encoded not in the nuclear genome but within the mitochondrial DNA, specifically inside a short open reading frame in the 12S ribosomal RNA gene. Its name is an abbreviation of that origin. It belongs to a small class of molecules called mitochondrial-derived peptides, a category that did not exist before the 2000s and that changed how the mitochondrion is understood: not solely as an organelle that produces energy and reports its status through metabolite levels, but as a genome that encodes its own signaling peptides.

The research interest in MOTS-c is concentrated on metabolism and on aging biology. In cell culture and in mouse models it has been reported to act on the folate one-carbon cycle in a way that indirectly activates AMP-activated protein kinase, the central cellular energy sensor, and under metabolic stress it has been observed translocating into the nucleus and associating with stress-response gene regulatory regions. Circulating MOTS-c has been measured in humans and reported to rise with exercise.

Response BioLabs supplies MOTS-c as a lyophilized powder for laboratory research use only. The distinction that matters most on this page is between what has been measured about endogenous MOTS-c in humans, which is real observational work, and what has been demonstrated about administering it, which has been done only in animals and cells.

The category preceded the molecule. In 2001 a peptide named humanin was identified from a short open reading frame within the mitochondrial 16S ribosomal RNA gene, which was the first demonstration that the mitochondrial genome encodes anything beyond the thirteen respiratory chain subunits, two ribosomal RNAs, and twenty-two transfer RNAs long assigned to it. That finding prompted systematic searches of the mitochondrial genome for additional coding regions.

MOTS-c was reported in 2015 by Changhan Lee, Pinchas Cohen, and colleagues at the University of Southern California, in a paper describing a short open reading frame within the 12S ribosomal RNA gene whose product they detected in tissue and plasma. The initial characterization reported effects on insulin sensitivity and adiposity in mice and proposed a mechanism running through the folate cycle rather than through a cell surface receptor, which distinguished it from most peptide signaling models.

Subsequent work extended the picture in three directions. A 2018 report described nuclear translocation of MOTS-c under metabolic stress and its association with chromatin at antioxidant response elements, which made it one of the few known mitochondria-encoded regulators of nuclear gene expression. Exercise physiology work in humans and rodents reported increases in MOTS-c in circulation and in skeletal muscle tissue following exercise. Population genetics work identified a mitochondrial DNA variant, m.1382A>C, producing a lysine to glutamine substitution at position fourteen of the peptide, which has been reported in Japanese cohorts in association with longevity and with lower prevalence of obesity and type 2 diabetes among males. Additional mitochondrial-derived peptides, including the small humanin-like peptides, have since been described.

MOTS-c is a linear sixteen-residue peptide with the sequence MRWQEMGYIFYPRKLR, molecular formula C101H152N28O22S2, and a calculated average molecular weight of approximately 2174.6 g/mol for the free base. CAS number 1627580-64-6 corresponds to this sequence. Researchers should note that supplier certificates for this peptide sometimes list a molecular weight several percent higher than the calculated free base value. That difference reflects counterion content, typically acetate or trifluoroacetate retained from purification, rather than a different molecule, and it is a reason to work from net peptide content rather than from gross powder mass when concentration accuracy matters.

The sequence contains no cysteine, so there is no disulfide bond and no folding requirement on reconstitution. It does contain two methionine residues, at positions one and six, which are the most oxidation-prone residues in the standard amino acid set. Methionine sulfoxide formation is therefore the degradation route to watch, and it is accelerated by air exposure, by trace metal contamination in buffers, and by extended time in solution. Oxidized peptide will show as a satellite peak sixteen mass units above the parent in mass spectrometry.

The peptide carries three arginines and one lysine against a single glutamate, giving it a net positive charge at physiological pH and generally good aqueous solubility. The tryptophan at position three provides a useful spectroscopic handle, since absorbance at 280 nm allows concentration verification independent of gravimetric assumptions. As with any peptide in this size range, adsorptive loss to glass and untreated plastic is measurable at low working concentrations and should be controlled with low-binding labware rather than ignored.

The mechanism proposed in the original characterization is indirect and unusual for a peptide. Rather than binding a cell surface receptor, MOTS-c was reported to interfere with the folate-dependent one-carbon cycle, specifically at methylenetetrahydrofolate dehydrogenase 2, which sits in the de novo purine biosynthesis route. Inhibition at that step causes accumulation of the intermediate AICAR, and AICAR is a well-characterized endogenous activator of AMP-activated protein kinase. In this model MOTS-c does not activate AMPK directly; it shifts a metabolic flux in a way that generates an endogenous AMPK activator.

AMPK activation is itself well characterized and provides a plausible downstream account of the reported metabolic observations. Activated AMPK promotes GLUT4 translocation and glucose uptake in skeletal muscle, increases fatty acid oxidation through inhibition of acetyl-CoA carboxylase, and suppresses anabolic pathways including mTORC1 signaling. Reported increases in muscle glucose uptake in mouse studies are consistent with this route.

A second and partly independent mechanism concerns nuclear translocation. Under metabolic stress such as glucose restriction or oxidative challenge, MOTS-c has been observed moving from the cytoplasm into the nucleus, where it associates with chromatin at antioxidant response elements alongside transcription factors including ATF1, and where it has been reported to influence expression of genes in the NRF2-associated stress response program. If confirmed, this places a mitochondria-encoded peptide in the position of directly communicating mitochondrial state to nuclear transcription, a form of retrograde signaling that is conceptually significant beyond this particular molecule.

Exercise responsiveness ties the two threads together in the working model, since exercise both raises AMPK activity and, in reported human and rodent measurements, raises MOTS-c levels. Whether the peptide is a mediator of exercise adaptation or a marker that rises alongside it has not been resolved, and the distinction is exactly the kind that observational human data cannot settle.

What is established: MOTS-c exists, its sequence is defined, and its origin in a short open reading frame within the mitochondrial 12S ribosomal RNA gene has been confirmed. It is detectable in human plasma and tissue by mass spectrometry and immunoassay. The broader category of mitochondrial-derived peptides is now accepted, with humanin and the small humanin-like peptides characterized alongside it.

What is supported in humans but only observationally: endogenous MOTS-c levels have been measured across age groups and reported to decline with age in some cohorts, and circulating levels have been reported to rise following exercise. Genetic association work has linked the m.1382A>C variant, which alters residue fourteen of the peptide, to longevity and metabolic phenotypes in specific populations. This is real human data, and it is correlational. It establishes that the peptide is present and that it varies with physiological state. It does not establish what happens when the peptide is administered.

What is animal-model or cell culture only: every functional finding that drives interest in this compound. The insulin sensitivity and adiposity results are mouse data. The AICAR and AMPK mechanism was established in cell culture and mouse tissue. The nuclear translocation work is cell culture. The reports concerning physical function and muscle homeostasis in aging are mouse data. There is no published interventional human trial of administered MOTS-c, no human pharmacokinetic characterization, and no human safety data.

The gap between the two categories is the thing to hold onto. It is genuinely interesting that a mitochondria-encoded peptide is measurable in human blood and responds to exercise. That observation supports investigating the peptide. It does not support any conclusion about what supplying it from outside would do in a human, and the published record contains nothing that would allow such a conclusion to be drawn.

The lyophilized powder is hygroscopic and is stored at -20 C or below for long-term inventory, with 2 to 8 C acceptable for short-term working stock. Vials are brought to room temperature before opening so that condensation does not form on cold powder, and are resealed promptly. Protection from light is standard practice, and matters somewhat more here than for peptides without aromatic and sulfur-containing residues.

For reconstitution, diluent is added slowly down the vial wall rather than onto the powder cake, and the vial is swirled gently or left to dissolve without agitation. Vortexing introduces shear and creates air-liquid interface, both of which promote aggregation and, for this sequence specifically, increase methionine oxidation by increasing dissolved oxygen contact. Buffers containing trace transition metals accelerate the same reaction, so metal-free water and clean labware are worth the attention.

Reconstituted stock is held at 2 to 8 C, protected from light, and aliquoted into single-use volumes. Repeated freeze and thaw cycles cause cumulative loss that is invisible in the vial and shows up only as unexplained variability between experiments. Because tryptophan is present at position three, concentration can be verified by absorbance at 280 nm, which is a more reliable figure than one calculated from powder mass given the counterion question discussed above. Label every aliquot with compound, lot, concentration, diluent, and preparation date.