MOTS-c: Discovery, Sequence and Physicochemical Properties

Discovery and naming

MOTS-c is a 16-residue peptide described in 2015 and named for its association with a sequence encoded in the mitochondrial 12S ribosomal RNA region. The name is a compact identifier used in literature and catalogues. Here it is used only as nomenclature: the description identifies the reported sequence context and does not make claims about biological function.

A source record should distinguish the peptide name from the underlying sequence and analytical evidence. A short name is convenient in a catalogue, while the sequence provides a more explicit chemical identifier. The stated CAS number for MOTS-c is 1627580-64-6. When comparing records, retain the spelling, hyphenation, sequence, and registry number as separate searchable fields; this supports reliable indexing across technical documents.

Sequence and residue composition

The specified sequence is MRWQEMGYIFYPRKLR, comprising 16 amino-acid residues in a defined order. The one-letter symbols correspond to methionine, arginine, tryptophan, glutamine, glutamic acid, methionine, glycine, tyrosine, isoleucine, phenylalanine, tyrosine, proline, arginine, lysine, leucine, and arginine. Sequence order is a defining feature, not merely a list of ingredients.

The chain contains two methionine residues and multiple residues with ionizable side chains, including arginine, glutamic acid, and lysine. These features contribute to the molecule’s analytical behavior and potential charge distribution. The sequence is commonly written without spaces, but spacing into residue groups can help visual checking provided that residue order remains unchanged.

Formula and molecular mass

The stated molecular formula is C101H152N28O22S2, and the molecular weight is 2174.6 g/mol. The two sulfur atoms are consistent with the two methionine residues in the sequence. Formula and nominal molecular weight offer useful reference values for analytical review, especially when checking mass-spectrometric assignments.

Observed mass signals may differ from a neutral-molecule value because instruments detect ions, often with associated charge and adducts. Reporting conventions, calibration, and sample composition should be considered when comparing an observed mass with the stated molecular weight. A difference should be evaluated in the context of the method rather than treated as a conclusion on its own.

Charge and chemical properties

MOTS-c includes several basic residues, notably arginine and lysine, and an acidic glutamic acid residue. Its net charge depends on the chemical environment and the protonation states of ionizable groups. Consequently, chromatographic retention and electrophoretic behavior can vary with pH, solvent composition, and method settings. A sequence-derived estimate is not a substitute for conditions specified in an analytical procedure.

The sequence also includes aromatic residues such as tryptophan, tyrosine, and phenylalanine. These structural features can influence ultraviolet absorbance and interactions with chromatographic stationary phases. Analytical methods should be selected and interpreted with the residue composition and sample matrix in mind.

Methionine oxidation sensitivity

Methionine contains a sulfur-bearing side chain that can be susceptible to oxidation during handling or storage. Oxidation changes the chemical composition and produces a corresponding mass shift that can be assessed by suitable mass-spectrometric methods. Because the sequence contains two methionines, an analytical record may need to distinguish unmodified material from one or more oxidized species.

Oxidation sensitivity is a chemical stability consideration, not a visual attribute. HPLC may reveal additional chromatographic species, while LC-MS can help evaluate their mass differences. Interpretation depends on sample preparation and method performance. Protecting the sealed material from unnecessary exposure to moisture, light, and unsuitable temperature conditions supports consistent material handling.

Analytical characterization

HPLC can assess a chromatographic profile under defined conditions, but reported peak-area purity depends on the method, detector, integration settings, and resolution of related species. LC-MS supports identity assessment by comparing observed ion signals with expected values, accounting for charge states and adducts. MALDI can provide complementary mass information with a different ionization approach.

Amino-acid analysis can assess residue composition after hydrolysis and appropriate preparation, though it does not independently establish sequence order. A robust identity record therefore draws on complementary methods and clearly states the scope of each result. Peptide content, chromatographic area, and sequence identity are distinct measures and should not be conflated.

Review a certificate of analysis for the lot identifier, test methods, dates, units, and meaning of each reported value. Where analytical limitations or acceptance criteria are stated, consider them when comparing lots or records. A method result is most useful when the sample identity and reporting basis are clear.

Mass data interpretation

When reviewing mass-based data, first identify whether the report gives a neutral mass, an observed ion, or a calculated value. Charge state and adduct assignment affect the displayed mass-to-charge ratio, so comparisons require the report’s stated convention. A concise worksheet can retain the observed signal, proposed assignment, reference value, and method notes as distinct entries instead of reducing them to one number.

For two methionine residues, a proposed oxidation-related signal should be described as an analytical assignment only when the method and evidence support it. Record the stated mass difference and the report’s interpretation without generalizing beyond the examined sample. Keeping this note linked to the lot, method revision, and sample identifier helps distinguish an observation from a sequence reference or a specification value.

When preserving a mass spectrum, keep the acquisition date and instrument method reference with the exported file. This provenance supports review of assignments without substituting a raw signal for a documented interpretation.

Storage and documentation

MOTS-c is supplied as lyophilized powder in a sealed glass vial. Store the sealed vial at 2–8 °C, protected from light and moisture. Maintain dry storage and avoid opening a cold container in a humid environment; allow the sealed vial to equilibrate to room temperature before opening the outer packaging. The powder should remain protected from avoidable environmental exposure.

The lot-matched COA can be verified through the NF7 site’s Verify a lot page. Match the vial label to its COA and retain the documentation with inventory records. MOTS-c ships within the United States in cold-chain packaging. On receipt, record the lot, inspect the shipment, and move the sealed vial into the specified storage range.