The secondary structure of the synthetic signal peptide of cytochrome c oxidase subunit IV (coxIV-25) has been measured by circular dichroism spectroscopy in different lipid environments. CoxIV-25 is polymorphic in membranes. It forms an amphiphilic α-helix both in negatively charged lipid bilayers (up to 49% helix) and in detergent micelles (up to 42% helix). In associaton with bilayers of the zwitterionic lipid phosphatidylcholine, coxIV-25 takes an aperiodic, unidentified structure. CoxIV-25 is also partially α-helical in bilayers of cardiolipin, mitochondrial lipid extracts and mixtures of synthetic phosphatidylcholine and phosphatidylglycerol.
