MOTS-c: structure and analysis

What is MOTS-c?

MOTS-c is a 16-amino-acid peptide encoded in the mitochondrial genome rather than the nuclear one — one of a small group of mitochondrial-derived peptides identified over the past two decades.

That genomic origin is what makes it unusual. Almost every peptide in this catalogue corresponds to a nuclear-encoded sequence or is entirely synthetic in design; this one is transcribed from mitochondrial DNA.

The sequence includes methionine and tryptophan residues, both of which have consequences for how the material behaves analytically.

How is MOTS-c produced?

Assembled by solid-phase peptide synthesis: the chain is built one residue at a time on an insoluble resin support, then cleaved from the resin, deprotected and purified — most commonly by reversed-phase high-performance liquid chromatography. The purified material is lyophilized to a dry solid.

The impurity profile that appears on a certificate is a record of where that process was imperfect: deletion sequences from an incomplete coupling, truncated chains, and species retaining a protecting group.

What are the molecular figures for MOTS-c?

Calculated from the formula C101H152N28O22S2, not measured. The average molecular weight counts the natural abundance of each element's isotopes; the monoisotopic mass is the mass of the single most abundant isotopic composition, which is the figure a mass spectrometer is usually compared against.

Two masses describe this molecule and they are not the same number. The monoisotopic mass assumes every carbon is carbon-12; the tallest peak in the isotope envelope sits 1 carbon-13 substitution above it, because for a molecule with 101 carbons that is the most probable composition. A specification or a database quoting the higher figure is not necessarily wrong — it is quoting the other peak, and both are given here.

Adducts, salts, modifications and multiply charged species all move an observed m/z away from any figure calculated here, and a certificate reports what was measured for a batch rather than what was expected of it.

What is the sequence of MOTS-c?

MOTS-c is 16 residues long. Written in the one-letter amino-acid code, as the cited record states it:

The sequence is what an identity test resolves. The mass a spectrometer is compared against is the mass this chain implies, which is why a single missing or substituted residue changes the result by an amount that cannot be mistaken for instrument variation — the deletion is detectable rather than invisible.

Sequence information describes the molecule, not the material in a vial. What establishes a specific batch is the identity method and result on its certificate.

How does MOTS-c compare with related compounds?

Related compounds are not interchangeable. Published figures differ between them, and in this catalogue three compounds share a GHRH backbone while several share the same structural class — which is exactly why identity is confirmed analytically rather than inferred from the label.

How is the identity of MOTS-c confirmed?

Mass spectrometry confirms the sixteen-residue chain. At this length a single deletion produces a clear mass shift and is readily detected.

Because the sequence contains methionine, the corresponding sulfoxide is a species an identity method will encounter: oxidation adds sixteen mass units, which is unambiguous at high resolution.

Which impurities can appear in MOTS-c?

Methionine oxidation is the characteristic impurity to expect. Methionine is among the most readily oxidised residues, and the sulfoxide product is a real and quantifiable impurity rather than a theoretical one — which is why a purity method for this compound needs to resolve it from the parent.

Tryptophan adds light sensitivity. It is the most photochemically labile of the standard amino acids, so light protection during storage is a reasonable precaution and photodegradation products are a plausible impurity class.

At sixteen residues the compound is well suited to reversed-phase separation: long enough to be properly retained, short enough that deletion products remain resolvable.

What does a certificate of analysis for MOTS-c report?

A certificate for a batch of this material names the batch, names the issuing laboratory, and states for each parameter both the method used and the specification the result was measured against. Identity and purity are the two core results; net peptide content states how much of the fill weight is actually peptide.

A certificate belongs to a batch, not to a product line. When a new batch is released it is tested again, and the certificate published against it is that batch's certificate — a previous batch's result is never carried forward.

Is MOTS-c for human use?

No. This page describes structure and analysis. It makes no claim about what this compound does, and none should be inferred from it. Material is supplied for laboratory research use only: it is not a drug, food, dietary supplement, cosmetic or medical device, it is not for human or veterinary consumption, and no dosing, administration or reconstitution guidance is provided for any such use.

References

• MOTS-c — PubChem, National Library of Medicine
• Mots-C — ChEMBL, European Bioinformatics Institute
• MOTS-c improves osteoporosis by promoting the synthesis of type I collagen in osteoblasts via TGF-β/SMAD signaling pathway — Eur Rev Med Pharmacol Sci, 2019