Molecule guides
Humanin: The First Mitochondrial-Derived Peptide and How to Work With It
A 24-residue peptide written into the 16S rRNA gene, found by a survival screen, and awkward enough in solution to deserve its own handling notes.
Humanin is a peptide of 24 amino acids whose gene lies inside the mitochondrial genome, in the MT-RNR2 region that codes for 16S ribosomal RNA, and it was the first mitochondrial-derived peptide anyone identified. No database search produced it. In 2001 researchers found it in a cDNA library built from the occipital cortex of an Alzheimer's brain, a region chosen precisely because its neurons had survived, and isolated it by screening for anything that shielded cells from amyloid-beta toxicity. That origin is why the humanin literature revolves around cytoprotection rather than metabolism.
Peptide Medix EU supplies Humanin as lyophilized powder in 5 mg and 10 mg vials within the mitochondrial peptides range.
Defining humanin
Humanin belongs to a small group of mitochondrial-derived peptides, products of short open reading frames tucked inside the ribosomal RNA genes of the 16.5-kilobase mitochondrial circle and detectable in both tissue and plasma. The sequence reads Met-Ala-Pro-Arg-Gly-Phe-Ser-Cys-Leu-Leu-Leu-Leu-Thr-Ser-Glu-Ile-Asp-Leu-Pro-Val-Lys-Arg-Arg-Ala; CAS 330936-69-1, formula C119H204N34O32S2, mass 2,687.27 g/mol.
Three features of that sequence govern its behaviour on the bench. Four leucines in a row at positions 9 to 12 form a markedly hydrophobic block that restricts solubility in water and promotes aggregation. The cysteine at position 8 has a free thiol capable of forming intermolecular disulfides, so dimers appear on standing. And the methionine at the N-terminus oxidises readily. None of this makes the peptide unworkable, but handling counts for more here than with an average short peptide.
Discovery and sequence variants
Nishimoto's group in Tokyo found it with a functional screen: transfect a cDNA library into cells under challenge from a familial Alzheimer's disease gene product and see which clones survive. The clone that did encoded humanin. Because its reading frame sits in mitochondrial DNA, humanin can be made on mitochondrial ribosomes using the mitochondrial genetic code, and a nuclear-encoded version translated in the cytosol has been described as well; the two differ at a single position, and papers are not always clear about which they used.
Modified sequences are common in the literature and are frequently what a given study actually tested. HNG is the best known, replacing serine 14 with glycine, and reports place it orders of magnitude above the parent sequence in protection assays. Rattin, the rodent counterpart, is longer than the human peptide. Reading humanin papers with care means checking the methods for which molecule was used.
Proposed mechanisms
Two mechanistic routes are described, and unusually for a peptide this size they operate on opposite sides of the plasma membrane.
Outside the cell, signalling runs through a receptor complex. Reports describe humanin binding a trimeric receptor assembled from ciliary neurotrophic factor receptor, WSX-1 and gp130, with signalling via the JAK/STAT3 pathway. Other work reports binding at formyl peptide receptor-like 1 (FPR2), a G-protein-coupled receptor that amyloid-beta also engages, offering a credible route for competitive interference there.
Inside the cell, the mechanism is protein-protein binding. Humanin is reported to bind Bax and prevent its move from cytosol to the mitochondrial outer membrane, the committing step of intrinsic apoptosis; comparable interactions are described with Bid and with IGF binding protein 3. This arm needs the peptide inside the cell, which its hydrophobic core plausibly allows.
Both routes arrive at the same reported endpoint, less apoptotic signalling under stress, which is why the literature calls humanin cytoprotective rather than metabolic or trophic. Which arm predominates in a given model is unsettled, and claiming one definitive mechanism for humanin would go beyond what has been published.
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
Plasma humanin is reported to fall with age in humans and in several animal species, and to run higher in some long-lived groups and in the children of centenarians. These remain association data.
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
No controlled human trials of administered humanin exist, and no approved product does either. A good deal of the strongest published data used HNG rather than the native sequence, a real caveat when applying results to the parent peptide. Background on the family is in humanin and the mitochondrial-derived peptide family, with the head-to-head in humanin vs MOTS-c.
Reconstitution and storage in the lab
Of everything on this shelf, humanin is the hardest to dissolve, and the leucine block is why. Bacteriostatic or sterile water is the usual solvent, though the material may need mild warming and time to stand; some published protocols dissolve it first in a little DMSO before diluting into aqueous buffer. Run the solvent down the vial wall, then swirl and leave it rather than shaking, since agitating a hydrophobic peptide encourages precisely the aggregation you are trying to prevent. A solution that remains cloudy has not fully dissolved and should not be treated as being at nominal concentration.
The figures are a lab calculation: 10 mg made up in 2 mL of diluent gives 5 mg/mL, or 5,000 mcg/mL, so 0.1 mL, the 10-unit mark on a U-100 syringe, holds 500 mcg. At 2,687.27 g/mol, 1 mg amounts to roughly 0.37 µmol. Method details are in our reconstitution guide.
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 rests on a mass spectrometry result matching 2,687.27 g/mol. Two satellite masses deserve particular attention with this sequence. A peak at +16 Da means the N-terminal methionine has oxidised. A peak near double the parent mass minus 2 Da means a disulfide-linked dimer has formed through the position 8 cysteine, a species that behaves differently in assays and that a purity percentage will not reveal if it co-elutes. On the chromatogram, remember that a hydrophobic 24-mer produces a broader peak than a small polar peptide, so judge peak shape against that expectation rather than against a textbook trace. Our guide to reading a peptide certificate of analysis handles the other sections.
Regulatory position
Humanin has no marketing authorisation as a medicine in any jurisdiction, no reference-listed product and no approved labelling, and it is not a food supplement. No approved use exists for it in any form, and material is supplied for laboratory research only.
Related compounds and further reading
The other widely used mitochondrially encoded peptide is MOTS-c, from the 12S rRNA region, whose reported mechanism is metabolic rather than cytoprotective. SS-31 (Elamipretide) is not encoded by mitochondria at all but engineered to concentrate at the inner membrane. For broader orientation, see our peptides for energy and mitochondria research overview.
Questions
How did researchers find humanin?
Through a functional screen instead of a database search. In 2001 a cDNA library from the occipital cortex of an Alzheimer's brain, selected because neurons there had survived, was transfected into cells challenged with a familial Alzheimer's gene product, and the clone that survived encoded humanin. That is why its literature centres on cytoprotection.
Which gene encodes humanin?
MT-RNR2 in the mitochondrial genome, the region coding for 16S ribosomal RNA. Humanin was the first mitochondrial-derived peptide identified, ahead of MOTS-c, which is encoded in the 12S rRNA region of the same circular genome.
What is HNG, and why does it matter?
HNG is the S14G analogue, with glycine in place of serine 14, reported to exceed the parent sequence in protection assays by orders of magnitude. Since much of the most striking humanin data was generated with HNG rather than the native peptide, it is worth checking the methods section of any paper.
Which mechanisms are reported for humanin?
Two, acting on either side of the membrane. Outside the cell it is reported to bind a trimeric CNTFR/WSX-1/gp130 receptor complex signalling via STAT3, and also FPR2. Inside the cell it is reported to bind Bax and block its translocation to the mitochondrial outer membrane, with similar interactions described for Bid and IGFBP-3.
Why is humanin difficult to dissolve?
Because positions 9 to 12 are four consecutive leucines, a strongly hydrophobic stretch that limits aqueous solubility and favours aggregation. Mild warming and time standing usually do the job; some protocols dissolve it in a small volume of DMSO first before diluting into aqueous buffer.
What should appear on the certificate of analysis?
A parent mass of 2,687.27 g/mol. Two satellites are important for this sequence: +16 Da marks oxidation of the N-terminal methionine, and a peak close to twice the parent mass minus 2 Da marks a disulfide-linked dimer formed via the cysteine at position 8.
Is there clinical evidence for humanin?
Not for administered peptide. The human data are observational: plasma humanin is reported to decline with age and to be higher in certain long-lived cohorts and in the offspring of centenarians. Interventional evidence comes from cells and rodents, and no product is approved anywhere.