MOTS-c: Research Chemistry and Literature

Origin and identification

Lee, Cohen and co-workers described the peptide in Cell Metabolism in 2015. The route to it was computational. Following the earlier identification of humanin, the mitochondrial genome was searched for further short open reading frames, and one lying within the 12S rRNA gene yielded a candidate that could then be detected as a real molecule. The name records that provenance: mitochondrial open reading frame of the twelve S ribosomal RNA type-c.

Endogenous material has since been measured in tissue and in circulating blood, by immunoassay and by mass spectrometry, in human and in rodent samples. Detection in circulation is what moved the peptide out of the category of computational curiosity and into the primary literature.

The sequence carries a documented natural variant. Fuku and colleagues reported the m.1382A>C substitution in a Japanese cohort, which replaces the lysine at position fourteen with glutamine and is largely confined to a single mitochondrial haplogroup. Synthetic material prepared for laboratory work follows the reference sequence unless a variant is specified. PubChem indexes the human peptide under CID 155885767.

Preclinical research context

Most of the primary work concerns metabolic regulation in rodents and in cultured muscle cells. The 2015 report followed mice on high-fat feeding and examined glucose handling, taking skeletal muscle as the tissue of interest. Untargeted metabolomics and isotope tracing in cell culture pointed to the folate one-carbon cycle, and to de novo purine biosynthesis downstream of it, as the pathway the peptide interferes with. Accumulation of the intermediate AICAR follows, and AICAR is an established activator of AMP-activated protein kinase. Phosphorylation of AMPK was the readout that tied the metabolomics to a signalling response.

A second line of work concerns where the peptide goes. Kim and colleagues reported in 2018 that MOTS-c moves into the nucleus of cultured human cells under metabolic stress, in a manner dependent on AMPK, and associates with transcription factors acting at antioxidant response elements. Subcellular fractionation, immunofluorescence, chromatin immunoprecipitation and RNA sequencing carried that argument. This is the mitochondrial-to-nuclear communication framing that most later papers adopt.

Reynolds and colleagues published in Nature Communications in 2021, covering mice at three ages, myoblast cultures placed under metabolic stress, and human skeletal muscle sampled around bouts of exertion. Transcriptional profiling of muscle and quantitation of the circulating peptide were the principal measurements. Review articles, including the 2023 survey by Zheng and colleagues, gather the wider set of rodent models, while the Fuku report situates the variant in a human genetic association context. Rodent and cell-culture findings are the substance of this field. Extrapolation beyond those systems is not supported by the experiments as published.

Analytical characterisation

Purity is assessed by reverse-phase HPLC. A C18 column run with an acetonitrile gradient in acidified water resolves the target from deletion sequences and from oxidised forms, with detection near 214 nanometres for the backbone. One tryptophan and two tyrosines also make the 280 nanometre channel usable, which gives a second and independent handle on concentration through the calculated extinction coefficient. Methionine oxidation is the impurity to watch. It adds sixteen mass units per residue and usually presents as an earlier-eluting shoulder on the main peak.

Mass spectrometry establishes that the observed mass agrees with the sequence. Electrospray ionisation of a peptide this basic returns a multiply charged envelope rather than a single protonated ion, and the doubly and triply charged species tend to dominate. Deconvolution should give a neutral mass consistent with C101H152N28O22S2. Tandem fragmentation supplies sequence coverage where identity, and not merely mass, is in question.

Testing is contracted to Janoshik Analytical and reported per lot. The certificate reproduces the chromatogram and the mass spectrum alongside the numerical result, which allows the shape of the trace to be judged rather than taken on trust. Match the lot number on the vial against the certificate before the material is put to any use.

Handling and storage

Lyophilised MOTS-c ships without refrigeration and is not harmed by the ambient conditions of ordinary transit. The dry solid is robust over the timescale of a shipment. What matters is where it goes on arrival, which is minus 20 degrees Celsius, in a freezer not subject to constant opening, with the vial sealed and dry.

Keep the material out of light. Tryptophan and tyrosine absorb in the ultraviolet, and photo-oxidation of those residues is well documented for peptides generally. An amber vial or the original carton is sufficient. There is no reason to leave a vial sitting under bench lighting while other work proceeds.

Once reconstituted, hold the solution at 2 to 8 degrees Celsius and work through it over a short window. If it must be kept longer, split it into aliquots sized for a single occasion and freeze those, because each freeze and thaw cycle costs intact peptide through aggregation and through solute concentration as ice forms. Thaw an aliquot once and do not return it to the freezer.

References

1. The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance
2. The Mitochondrial-Encoded Peptide MOTS-c Translocates to the Nucleus to Regulate Nuclear Gene Expression in Response to Metabolic Stress
3. MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis
4. The mitochondrial-derived peptide MOTS-c: a player in exceptional longevity?
5. MOTS-c: A promising mitochondrial-derived peptide for therapeutic exploitation
6. MOTS-c (human), PubChem Compound Summary CID 155885767

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