SS-31 (also known as elamipretide) is a small aromatic-cationic tetrapeptide built from an alternating pattern of positively charged and aromatic residues, a design that gives it distinctive cell-targeting behavior. Its four-residue length places it among the smallest peptides used as targeted research tools, yet its sequence is highly engineered.
Aromatic-cationic motif
The defining structural feature is an alternating arrangement of basic (positively charged) and aromatic side chains. This charge-and-aromatic pattern is what lets the peptide concentrate at the highly polarized inner mitochondrial membrane, the structural basis of its mechanism of action. Why residue identity and ordering drive such behavior is covered in understanding amino acid sequences.
Non-natural residues
SS-31 incorporates modified aromatic residues — notably 2',6'-dimethyltyrosine (Dmt) — that are introduced during synthesis rather than found in standard proteins. These non-natural building blocks contribute both to the peptide's targeting behavior and to its resistance to enzymatic degradation, a common goal in designed peptide chemistry.
Charge and membrane affinity
The net positive charge is central to how the peptide accumulates: it is drawn toward the strongly negative electrochemical environment of the inner mitochondrial membrane, while the aromatic residues anchor it there. The balance of these two properties is deliberately tuned by residue choice.
Synthesis
Its short length suits solid-phase peptide synthesis, where the chain is assembled on resin one protected residue at a time, including the non-natural aromatic units. After cleavage and deprotection, the crude peptide is purified by preparative chromatography.
Drying and quality control
The purified peptide is lyophilized (what is lyophilization) into a stable powder and verified by HPLC for purity and by mass spectrometry for the expected molecular weight. Overview: SS-31 research overview.
Sequence verification beyond molecular mass
Because stereoisomers and positional isomers can share the same nominal mass, mass spectrometry alone cannot establish every structural feature of SS-31. Chromatographic retention, high-resolution mass data, and documented starting-material stereochemistry provide complementary evidence that the intended tetrapeptide was produced. The dimethylated aromatic residue can also generate synthesis-specific impurities if coupling or deprotection is incomplete. Careful purification is therefore essential even for a four-residue chain. This analytical point is functionally relevant: mitochondrial partitioning depends on the precise alternation of charge and aromaticity, so an isomeric or deletion impurity may not reproduce the localization behavior of the target sequence.
Product page: SS-31 research vials.
Research Use Only. Supplied strictly for laboratory research and development — not for human or veterinary use, consumption, or any therapeutic or diagnostic purpose. This article is research education, not usage guidance.