MOTS-c: Molecular Characterization and Mitochondrial-Derived Peptide Biology — A Research Reference

Mitochondria carry their own small circular genome, separate from nuclear DNA, encoding a handful of proteins along with the transfer and ribosomal RNAs the organelle uses for its own translation. MOTS-c is encoded by a short open reading frame contained within one of those RNA genes: the 12S ribosomal RNA gene. The name compresses that description — mitochondrial open reading frame of the twelve S ribosomal RNA, type c [1].

That placement makes it a member of the mitochondrial-derived peptides, a class defined by genomic origin. Humanin, encoded within the 16S ribosomal RNA gene, was the first recognized, and its characterization prompted the search that produced the others [3]. The class label describes provenance rather than structural similarity, and the members do not resemble one another in sequence.

The peptide is a sixteen-residue linear chain: methionine-arginine-tryptophan-glutamine-glutamate-methionine-glycine-tyrosine-isoleucine-phenylalanine-tyrosine-proline-arginine-lysine-leucine-arginine, with a molecular weight of approximately 2,175 daltons. Three arginines and a lysine make it strongly basic. The composition worth noting for handling is the pair of methionines and the tryptophan — three residues drawn from the most oxidation- and light-sensitive end of the amino acid set.

No cell-surface receptor has been established for this peptide, which distinguishes it from most compounds in this catalogue and shapes what can meaningfully be assayed.

The characterized behaviour that has attracted most attention is subcellular relocation: under defined stress conditions in vitro the peptide moves from the cytosol into the nucleus, where it associates with chromatin and has been reported to influence transcription of nuclear-encoded genes [2]. That places its mechanism in the domain of protein-DNA and protein-chromatin interaction rather than receptor pharmacology — an unusual position for a synthetic peptide sold as a research compound, and one that dictates the relevant assay format.

The practical consequence for experimental design is that receptor binding assays have no target here. Localization imaging, chromatin association, and transcriptional readouts are the informative formats, and the stress condition applied to the system is a primary experimental variable rather than a background detail, since the relocation is conditional rather than constitutive [2].

Sequence conservation is a further consideration. The mitochondrial genome varies between species, and the reading frames encoding this class of peptide vary with it, so sequences reported for non-human organisms differ at several positions. Cross-species literature comparisons should be read with the exact sequence in hand.

Mass spectrometry confirms the intact mass near 2,175 daltons. For this sequence the measurement also reports on oxidation state: each oxidized methionine adds a defined sixteen-dalton increment, so a batch carrying sulfoxide forms shows satellite masses above the target at plus sixteen and plus thirty-two. Their absence is part of what a clean identity result asserts.

Reversed-phase HPLC resolves the main peak from related substances and yields the purity figure. A sixteen-residue synthesis produces the familiar deletion sequences, where a residue failed to couple; the compound-specific related substances are the methionine sulfoxide forms, which separate from the unoxidized peptide and typically elute close to the main peak. Reading the chromatogram near the main peak against the mass data is how the two methods corroborate one another here.

Net peptide content accounts for counter-ions and residual water, determining how much peptide a nominal milligram figure represents.

Sealed lyophilized material is stable at ambient temperature for the duration of transit and requires no cold chain in shipping. On receipt, vials are refrigerated and kept out of direct light.

Reconstituted material is held refrigerated and used within the window the receiving facility's protocols specify, and repeated freeze-thaw cycling is avoided.

This sequence sits at the sensitive end of the storage spectrum. Two methionines give it twice the usual exposure to the most common oxidation route, and the tryptophan is photosensitive — so light protection and limiting time in solution matter more here than for robust sequences. Minimising how often a vial is opened, and keeping solutions in amber glass or foil-wrapped during extended handling, is standard practice for a composition like this one.

The strongly basic character makes the peptide well behaved in mildly acidic aqueous media, and at sixteen residues it dissolves readily without mechanical assistance.

MOTS-c is an investigational compound. It has not been approved by the FDA or any other regulatory authority, and no manufacturing, labeling, or quality standards for an approved product apply to it. Research material is sold strictly for laboratory research use; it must not be administered to humans or animals. Researchers are responsible for compliance with all institutional and jurisdictional requirements governing research chemicals.

Each batch of research-grade MOTS-c is accompanied by an independent certificate of analysis specific to that lot.

MOTS-c is a sixteen-residue linear peptide of approximately 2,175 daltons, encoded by a short open reading frame within the mitochondrial 12S ribosomal RNA gene and belonging to the mitochondrial-derived peptide class alongside humanin. No cell-surface receptor has been established for it; its characterized in-vitro behaviour centres on conditional relocation to the nucleus and association with chromatin, which makes localization and transcriptional readouts the informative assay formats. Analytical verification rests on mass confirmation without methionine sulfoxide satellites, chromatographic resolution of oxidized and deletion species, and batch-specific net peptide content.