Melittin-Diacylphosphatidylcholine Interaction Examined by Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

Abstract

The structure of melittin in the presence of dioleoylphosphatidylcholine (DOPC) was investigated using hydrogen-deuterium (H/D) exchange in conjunction with collision induced dissociation (CID) in an rf-only hexapole ion guide with electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS). The deuterium incorporation into backbone amide hydrogens of melittin in the presence of DOPC was analyzed at different time points examining the mass of each fragment ion produced by hexapole-CID. The percentage of deuterium incorporation into the fragments of melittin was less than 45% at initial 10 s of isotope exchange. It increased rapidly as the exchange period was prolonged. After 300 s of incubation in D2O about 85% of amide hydrogens were exchanged with deuterium. When melittin was incubated in D2O in the presence of dodecylphosphocholine (DPC), the rate of isotope exchange was reduced at every time point. In the case of melittin alone, more than 80% amide hydrogens were exchanged with deuterium within 10 s. By comparing these time courses, it seems that the contact with DOPC did not induce melittin to change its conformation. DOPC possibly just shielded the melittin molecule while DPC induced melittin to form some stable conformation, such as helical structure. It was revealed that H/D exchange and MS analysis enabled to study such structural changes of a peptide brought about by the interaction with two types of phospholipid even in the presence of 50-fold amount of lipid.