SS-31

SS-31 is a four-residue peptide with an alternating cationic and aromatic motif that gives it an unusual property: it crosses cell membranes without a transporter and then accumulates specifically at the inner mitochondrial membrane, where it binds cardiolipin. Cardiolipin is a phospholipid essentially unique to that membrane, so the binding delivers a targeting selectivity that most mitochondrially-directed compounds achieve only through bulky lipophilic cations.

The published mechanism concerns cardiolipin-cytochrome c interaction, cristae architecture and electron transport chain efficiency, with research applications in ischaemia-reperfusion, mitochondrial myopathy and age-related mitochondrial decline models. It contains 2,6-dimethyltyrosine, a non-natural residue that is expensive and where poor-quality lots cut corners — substitution with ordinary tyrosine gives a near-mass peptide with different properties. Our identity confirmation is specifically set up to catch that substitution.