Localization of Intramolecular Monosulfide Bridges in Lantibiotics Determined with Electron Capture Induced Dissociation

Electron capture induced dissociation (ECD) and collisionally activated dissociation (CAD) experiments were performed on four lanthionine bridge-containing antibiotics. ECD of lantibiotics produced mainly c and z. ions, as has been observed previously with other peptides, but more interestingly, the less common c. and z ions were observed in abundance in the ECD spectra. These fragments specifically resulted from the cleavage of both a backbone amine bond and the thioether bond in a lanthionine bridge. ECD seemed to induce mainly cleavages near the lanthionine bridges. This fragmentation pattern indicates that lanthionine bridges play a key role in the selectivity of the ECD process. A new mechanism is postulated describing the formation of c. and z ions. Comparative low-energy CAD did not show such specificity. Nondissociative ECD products were quite abundant, suggesting that relatively stable double and triple radicals can be formed in the ECD process. Our results suggest that ECD can be used as a tool to identify the C-terminal attachment site of lanthionine bridges in newly discovered lantibiotics.