Humanin: The First Mitochondrial-Derived Peptide and How to Work With It

Humanin is a 24-residue peptide encoded not in the nucleus but in mitochondrial DNA — within MT-RNR2, the gene for 16S ribosomal RNA — and it holds the distinction of being the first mitochondrial-derived peptide ever described. It was not predicted by bioinformatics. In 2001 a team working with a cDNA library from the occipital cortex of an Alzheimer's patient (an area picked because its neurons had been spared) pulled it out of a screen for sequences that protected cells against amyloid-beta toxicity. That discovery route explains why research on humanin is dominated by cell protection rather than by metabolism.

We supply Humanin freeze-dried in 5 mg and 10 mg vials, as part of our mitochondrial peptides range.

Defining humanin

Humanin is one of a handful of mitochondrial-derived peptides — short open reading frames hidden within the rRNA genes of the circular, 16.5-kilobase mitochondrial genome, whose products can be measured in tissues and in plasma. Its sequence is Met-Ala-Pro-Arg-Gly-Phe-Ser-Cys-Leu-Leu-Leu-Leu-Thr-Ser-Glu-Ile-Asp-Leu-Pro-Val-Lys-Arg-Arg-Ala. Identifiers: CAS 330936-69-1, formula C119H204N34O32S2, molecular weight 2,687.27 g/mol.

At the bench, three features of the sequence dictate how it behaves. Residues 9 to 12 are four consecutive leucines — a strongly hydrophobic patch that limits water solubility and drives aggregation. Cys8 carries a free thiol that can link two molecules by a disulfide, so dimers accumulate over time. And the N-terminal methionine is easily oxidised. The peptide is perfectly usable, but handling matters more than it does for a typical short peptide.

Discovery and sequence variants

The discovery came from Nishimoto and colleagues in Tokyo, using a survival screen: they introduced a cDNA library into cells exposed to the product of a familial Alzheimer's disease gene and looked for clones that kept the cells alive. The surviving clone encoded humanin. Since its open reading frame lies in mitochondrial DNA, the peptide can be translated on mitochondrial ribosomes with the mitochondrial genetic code; a cytosolic version translated from a nuclear copy has also been reported. The two forms differ by one residue, and published methods do not always make clear which was studied.

Many papers actually tested a modified sequence rather than native humanin. The most widely used is HNG, in which Ser14 is swapped for glycine; it is reported to be several orders of magnitude more potent than the parent in protection assays. The rodent homologue, rattin, is a longer peptide than the human one. When reading humanin literature, always confirm from the methods which molecule was used.

Proposed mechanisms

Published work describes two mechanisms — and, unusually for such a small peptide, one operates outside the cell and the other inside it.

On the cell surface, humanin is reported to signal through a receptor complex. One proposed receptor is a trimer of the ciliary neurotrophic factor receptor, WSX-1 and gp130, signalling via JAK/STAT3. Another reported binding partner is FPR2 (formyl peptide receptor-like 1), a GPCR that amyloid-beta also binds — a plausible site for competition between the two.

Within the cell, the proposed mechanism is direct binding to other proteins. Humanin is reported to hold Bax in the cytosol and stop it moving to the outer mitochondrial membrane, the step that commits a cell to the intrinsic death pathway. Bid and IGF binding protein 3 have been named as further binding partners. For this intracellular route to work, humanin has to cross the plasma membrane — something its greasy central stretch could plausibly enable.

Both routes lead to the same reported result — reduced apoptotic signalling in stressed cells — which is why humanin is described as cytoprotective rather than metabolic or trophic. Which route dominates in any particular model has not been settled, and asserting a single definitive mechanism would overstate the published evidence.

Research to date

Neuronal survival and amyloid work

The founding and still largest literature covers protection of cultured neurons from amyloid-beta toxicity and from familial Alzheimer's gene products, extending to rodent memory-impairment models in which the peptide or HNG was given centrally. All of it is cell and animal work.

Metabolic and insulin studies

Rodent experiments have examined glucose handling and insulin sensitivity, reporting effects on hypothalamic signalling and on hepatic glucose output. Observational human studies have also reported correlations between circulating humanin and measures of insulin sensitivity.

Aging and longevity cohorts

Circulating humanin levels are reported to decline with age in people and in several animal species, and to be higher in certain long-lived populations and in centenarians' offspring. These are correlations, not evidence of cause.

Cardiovascular and endothelial work

Studies in ischaemia-reperfusion, atherosclerosis and endothelial cell models report fewer apoptotic markers and better preserved function, in line with the cytoprotective framing.

What remains unproven

There are no controlled trials of humanin given to people, and there is no approved product. Much of the most compelling published work used HNG instead of the native peptide — an important caveat when transferring conclusions to humanin itself. For family background see humanin and the mitochondrial-derived peptide family; for a direct comparison, humanin vs MOTS-c.

Reconstitution and storage in the lab

Humanin is the most difficult peptide in this range to get into solution, because of that leucine patch. Bacteriostatic or sterile water is the usual starting point, but it may take gentle warming and some standing time; a number of published methods dissolve the powder in a small volume of DMSO and then dilute into aqueous buffer. Let the solvent run down the side of the vial, swirl, and let it sit — shaking a hydrophobic peptide promotes exactly the aggregation you want to avoid. If the solution stays cloudy, it is not fully dissolved and its concentration is not what you calculated.

Bench arithmetic: 10 mg in 2 mL of diluent gives 5 mg/mL (5,000 mcg/mL), so 0.1 mL — the 10-unit line on a U-100 syringe — contains 500 mcg. With a molecular weight of 2,687.27 g/mol, 1 mg corresponds to about 0.37 µmol. The reconstitution guide covers the method in detail.

Keep lyophilized vials sealed at −20 °C, protected from light and moisture. Hold reconstituted material at 2-8 °C during the study period or aliquot and freeze it; because the free cysteine thiol makes dimerisation on standing a genuine risk, freshly made solution beats long-stored stock. Wider practice is covered in how to store peptides.

Purity and reading the COA

Identity is confirmed by a mass spectrometry result of 2,687.27 g/mol. For this sequence, two side peaks are worth looking for. A signal 16 Da above the parent points to oxidation of the N-terminal methionine. A signal at roughly twice the parent mass, less 2 Da, points to a dimer joined through Cys8 — a species that behaves differently in assays and, if it co-elutes, will not be reflected in the purity figure. When judging the chromatogram, expect a hydrophobic 24-mer to give a wider peak than a small polar peptide, and assess the shape with that in mind rather than comparing it with an idealised trace. The remaining sections are explained in our guide to reading a peptide certificate of analysis.

Regulatory position

Humanin is not authorised as a medicine in the EU, the US or any other jurisdiction; there is no reference product and no approved label, and it is not a food supplement either. It has no approved use in any form, and we supply it solely for laboratory research.

Related compounds and further reading

MOTS-c is the other mitochondrially encoded peptide in common use; it comes from the 12S rRNA region and its reported mode of action is metabolic, not cytoprotective. SS-31 (Elamipretide), by contrast, is not mitochondrially encoded at all — it is a synthetic peptide designed to accumulate at the inner mitochondrial membrane. Our peptides for energy and mitochondria research overview puts all of these in context.

Matching catalogue section: Mitochondrial Peptides