MOTS-c: Molecular Structure

Molecular Structure and Properties#

MOTS-c is a 16-amino acid peptide with the sequence MRWQEMGYIFYPRKLR and a molecular weight of approximately 2174.6 Da. Its molecular formula is C101H152N28O22S2, and it carries CAS number 1627580-64-6. Unlike the vast majority of bioactive peptides studied in research, MOTS-c is encoded within the mitochondrial genome rather than the nuclear genome, making it a member of the mitochondrial-derived peptide (MDP) family.

Amino Acid Sequence#

The primary structure of MOTS-c is Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg. In single-letter notation this reads MRWQEMGYIFYPRKLR. The peptide is 16 residues in length and contains two methionine residues (positions 1 and 6), two tyrosine residues (positions 8 and 11), two arginine residues (positions 2 and 16), and a single tryptophan (position 3). The C-terminal region is enriched in basic residues (Arg-Lys-Leu-Arg), conferring a net positive charge at physiological pH.

The presence of tryptophan and two tyrosine residues gives the peptide significant aromatic character, while the two methionine residues introduce sulfur-containing side chains that are susceptible to oxidation. The proline at position 12 introduces a rigid kink in the backbone, which may influence the peptide's conformational preferences in solution.

No experimentally determined three-dimensional structure (e.g., NMR or X-ray crystallography) for MOTS-c has been deposited in the Protein Data Bank as of the current date. Given its short length, MOTS-c is expected to adopt a largely disordered conformation in aqueous solution, though transient secondary structure formation cannot be excluded, particularly around the proline residue.

Mitochondrial Genome Origin#

MOTS-c is encoded within the mitochondrial 12S ribosomal RNA gene (MT-RNR1), located on the heavy strand of the mitochondrial genome. Its discovery in 2015 by Lee et al. revealed the existence of a short open reading frame (sORF) embedded within what was previously considered a non-coding ribosomal RNA gene. This finding challenged the traditional view that the mitochondrial genome encodes only 13 proteins, 22 transfer RNAs, and 2 ribosomal RNAs.

The MOTS-c coding sequence is located within the 12S rRNA gene at positions corresponding to the sORF that produces the 16-amino acid peptide. The sORF is translated using the mitochondrial genetic code, which differs from the standard nuclear genetic code in several codon assignments. This mitochondrial origin means that MOTS-c is maternally inherited, as mitochondrial DNA is transmitted exclusively through the maternal lineage.

The existence of functional sORFs within ribosomal RNA genes suggests that the mitochondrial genome has greater informational content than previously appreciated. MOTS-c joins humanin (encoded within the 16S rRNA gene) and the small humanin-like peptides (SHLPs 1-6, also from the 16S rRNA gene) as recognized mitochondrial-derived peptides.

Chemical Properties#

The isoelectric point of MOTS-c is estimated to be in the basic range (approximately pH 11) due to the predominance of basic residues (three arginines and one lysine) over acidic residues (one glutamic acid). At physiological pH, the peptide carries a net positive charge of approximately +3, which may contribute to its capacity for electrostatic interactions with negatively charged molecules such as DNA and phospholipid membranes.

Folate and Methionine Metabolism Link#

A defining feature of MOTS-c's mechanism of action is its direct interference with the folate cycle and one-carbon metabolism. MOTS-c inhibits the mitochondrial enzyme methylene-tetrahydrofolate dehydrogenase/cyclohydrolase 2 (MTHFD2), which is a key enzyme in the folate cycle responsible for generating the one-carbon units required for de novo purine biosynthesis.

Inhibition of MTHFD2 by MOTS-c leads to accumulation of the intermediate 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) in the de novo purine biosynthesis pathway. AICAR is an endogenous activator of AMP-activated protein kinase (AMPK), and its accumulation provides the mechanistic link between MOTS-c and AMPK activation. This pathway distinguishes MOTS-c from other AMPK activators such as metformin (which inhibits mitochondrial complex I) or direct pharmacological AMPK agonists.

The connection between MOTS-c and folate metabolism also has implications for methionine cycling, as the folate cycle and methionine cycle are metabolically coupled through the transfer of one-carbon units. Disruption of folate metabolism by MOTS-c could therefore have downstream effects on S-adenosylmethionine (SAM) production, DNA methylation, and other methionine-dependent processes, though these effects have not been extensively characterized in the literature.

Stability and Formulation Considerations#

Detailed stability data for MOTS-c under various conditions have not been extensively published. As a short peptide containing two methionine residues and no disulfide bonds, MOTS-c is expected to be susceptible to proteolytic degradation in plasma and to oxidative modification of its methionine side chains.

The half-life of MOTS-c in circulation has not been well characterized in published pharmacokinetic studies. Endogenous MOTS-c has been detected in human plasma, indicating that it circulates systemically, but the kinetics of exogenous MOTS-c administration remain largely undescribed in the peer-reviewed literature.

For research purposes, synthetic MOTS-c is typically supplied as a lyophilized powder and reconstituted in aqueous buffers. Standard peptide handling precautions apply, including storage at low temperatures to minimize degradation, avoidance of repeated freeze-thaw cycles, and protection from oxidizing conditions that could modify the methionine residues.

Longevity-Associated Polymorphism#

A naturally occurring mitochondrial DNA polymorphism (m.1382A>C) within the MOTS-c coding sequence results in a lysine-to-glutamine substitution at position 14 of the peptide (K14Q). This variant, identified in Japanese and Northeast Asian populations, has been associated with exceptional longevity in epidemiological studies. The K14Q substitution replaces a positively charged lysine with an uncharged glutamine, reducing the net positive charge of the peptide from approximately +3 to approximately +2 at physiological pH. This charge reduction could alter MOTS-c's interactions with negatively charged binding partners, including DNA during nuclear translocation and chromatin interaction.

The functional consequences of this polymorphism on MOTS-c biological activity remain under active investigation. Whether the K14Q variant has altered AMPK-activating potency, different nuclear translocation kinetics, or modified interactions with MTHFD2 has not been definitively established. The restriction of this longevity association to East Asian populations raises questions about population-specific genetic backgrounds and environmental factors that may modulate the functional significance of this variant.

Related Reading#

• MOTS-c overview and research guide
• Peptides similar to MOTS-c
• MOTS-c research evidence