Structure of melittin bound to phospholipid micelles studied using hydrogen-deuterium exchange and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

The structure of melittin bound to dodecylphosphocholine (DPC) micelles was investigated using hydrogen-deuterium (H/D) exchange in conjunction with c ollision induced dissociation (CID) in an rf-only hexapole ion guide with e lectrospray ionization-Fourier transform ion cyclotron resonance mass spect rometry (ESI-FTICR MS). The deuterium incorporation into backbone amide hyd rogens of melittin with or without DPC micelles was analyzed at different t ime points examining the mass of each fragment ion produced by hexapole CID . When melittin existed alone in aqueous solution, more than 80% of amide h ydrogens was exchanged within 10 s, and the deuterium content in each fragm ent ion showed high values throughout the experiments. When melittin was bo und to DPC micelles, the percentage of deuterium incorporation into the fra gment decreased remarkably at any time point. It increased Little by little as the exchange period prolonged, indicating that some stable structure wa s formed by the interaction with DPC. The results obtained here were consis tent with the previous studies on the helical structure of melittin carried out by NMR and CD analyses. The strategy using H/D exchange and MS analysi s might be useful for studying structural changes of peptides and proteins caused by phospholipid micelles. It could also be applied to membrane-bound proteins to characterize their structure. (C) 2001 American Society for Ma ss Spectrometry.