Trifluoroethanol (TFE)-induced conformational changes in dynorphin A (1–13) were investigated using charge-state distribution (CSD) and hydrogen–deuterium exchange (HDX), combined with electrospray ionization (ESI) mass spectrometry (MS). Individual amino acids involved in secondary structural elements were identified by collision-induced dissociation-tandem mass spectrometry (MS/MS). It was observed that dynorphin A (1–13) largely exists in an unfolded conformation and a folded structure in increasing concentrations of TFE. In 50% TFE, it forms an α-helix that encompasses residues 1–9 and remains flexible from residues 10 to 13.

Keywords: conformation, dynorphin A (1–13), hydrogen–deuterium exchange, trifluoroethanol, electrospray-ionization, charge- state distribution, tandem mass spectrometry, opioid peptide, amino acid sequence, collision-induced dissociation