Microheterogeneity characterization of a paracelsin mixture from Trichoderma reesei using high-energy collision-induced dissociation tandem mass spectrometry

The microheterogeneity of the paracelsin mixture broth of Trichoderma reesei was analysed using mass spectrometric methods, in particular high energy collision-induced dissociation (CID) tandem mass spectrometry (MS/MS). Based on the liquid secondary ion mass spectrum of the mixture, there are three main components, with molecular masses M and (M +/- 14), together with two minor components of molecular weight (M +/- 28). The high-energy CID tandem mass spectra of both the protonated and sodiated molecules yielded abundant and characteristic fragment ions, but of very different types. It was found that a paracelsin peptaibol in a mixture could be successfully sequenced based on the tandem mass spectra of its protonated and sodiated molecules or, alternatively, on the tandem mass spectra of its y(7) and b(13) fragment ions. A terminology for indicating these sequential peptide fragments is proposed. To determine the sequence of new analogues, tandem mass spectra of the y(7), (y(7) +/- 14), b(13), (b(13) +/- 14) and (MH +/- 14) positive ions were also taken. Based on these experiments, four new paracelsin components (PA-F, PA-G, PA-H and PA-I) were sequenced successfully. The microheterogeneity of the mixture was found to be more pronounced than had been assumed previously. In these new analogues, besides positions 6 and 9, position 17 is also involved in the exchange. MS/MS studies on minor fragment ions, such as (b(13) - 28) and (b(8) - 14) show further microheterogeneity at positions 3, 5, 10 and 12, which increase the number of possible minor components.