Comparison of collisionally activated dissociation mass spectra for the identification of cyclopeptides and cyclodepsipeptides

Abstract

Collisionally activated dissociation (CAD) spectra of protonated molecules of cyclopeptides and cyclodepsipeptides obtained with two different mass spectrometry systems were compared. Fragmentations were obtained either from collisions induced in the ion source of an electrospray mass spectrometer fitted with a single quadrupole by increasing the extracting cone voltage or from collisions with an inert gas in a free-field area of a fast-atom bombardment (FAB) mass spectrometer. Similar fragmentation pathways were produced with the two configurations even though actual tandem mass spectrometry experiments with magnetic and electric sectors provided more information than cone-induced dissociations. However, only the latter mode allowed us to perform mass spectrometric analyses coupled to liquid chromatography (LC/ ESI-MS) at low cost on commercially widespread instruments. Copyright # 1999 John Wiley & Sons, Ltd. Received 15 January 1999; Revised 8 March 1999; Accepted 9 March 1999 The development of fast-atom bombardment (FAB) mass spectrometry 1 provides easy identification of polar compounds in particular of peptides.2 Furthermore, the more recent electrospray ionization (ESI) technique 3 allows the analysis of mixtures by readily coupling mass spectrometry to liquid chromatography (LC/ESI-MS). 4 Although other techniques can be applied for the characterization of linear peptides, the recourse to mass spectrometry is compulsory for the identification of cyclic structures. Indeed such compounds lacking a free N-terminal group are not suitable for Edman degradation or amino acid analysis. Besides, the presence of N-alkylated residues, frequently observed in natural cyclic peptides, hampers the sequence determination by these techniques.Mass spectrometric analysis of cyclopeptides has been reviewed 5 and FAB mass spectra of various cyclopeptides have been studied in our laboratory. 6-11The limited number of fragmentations that are generally observed in the mass spectrum of a peptide led to the use of tandem mass spectrometry 12 to produce relevant sequence information. Nevertheless, in the case of ESI-MS experiments, it has been reported in the literature 13 that characteristic sequence ions can also be produced without the necessity for classical tandem mass spectrometry. It was found that collision-induced dissociation could be achieved by increasing the voltage of the sampling cone before the analyzer entrance. These results were particularly interesting as peptide sequencing could be achieved from LC/ESI-MS undertaken with standard equipment fitted with a single quardrupole. 13 Thus, it seemed interesting to verify whether previous results 6,7 obtained for the cyclic tetrapeptide tentoxin with a double-focusing mass spectrometer of the EB design fitted with a FAB ion source could be reproduced with a single quardrupole ESI mass spectrometer. A second series of cyclic hexapeptides and derived depsipeptides from the destruxin family was also submitted to such comparative studies. Our aim was to assess if the s...

Identification and Characterization of a Library of Microheterogeneous Cyclohexadepsipeptides from the Fungus Isaria

“…Further, the peaks at m / z 512.2, 568.3, 610.3 (Figure ) and 540.3 (Figure a), which are due to CO loss from their respective precursor ions, [M + H − CO] + , confirm the cyclic nature of the peptide . The observation of CO loss concomitant with the loss of H 2 O from the protonated precursor ion confirms that P1, P3, P6, and P13 are indeed cyclodepsipeptides, more specifically, isariins.…”

“…Further, the peaks at m/z 512.2, 568.3, 610.3 (Figure 2) and 540.3 (Figure 4a), which are due to CO loss from their respective precursor ions, [M + H -CO] + , confirm the cyclic nature of the peptide. 12 The observation of CO loss concomitant with the loss of H 2 O from the protonated precursor ion confirms that P1, P3, P6, and P13 are indeed cyclodepsipeptides, more specifically, isariins. Cyclodepsipeptides, isolated from Isaria, characterized by the presence of a D-β-hydroxy acid ( D β-HA), D Leu, and absence of aromatic amino acid residues have been named as isariins.…”

Structure elucidation of cyclic pyoverdins and examination of rearrangement reactions in MS/MS experiments by determination of exact product ion masses

“…The most important in number and efficiency among these molecules, referred to as pyoverdins , have a dihydroxyquinoline chromophore linked to the N ‐terminus of a peptide chain, which comprises 6–12 amino acids, either as an open chain or forming in part cyclic substructures. Such cycles can be formed by an amidation reaction of the C ‐terminal carboxyl group with the free amino group of an in‐chain Lys or Orn, or with the hydroxyl group of an in‐chain Ser or Thr, thus forming an ester bond 2. In addition, the amino acids can be modified to form Fe 3+ chelating ligands such as β‐hydroxy‐Asp (OHAsp) or δ‐ N ‐acyl‐δ‐ N ‐hydroxy‐Orn (Fho).…”

Sequence Elucidation of an Unknown Cyclic Peptide of High Doping Potential by ETD and CID Tandem Mass Spectrometry

“…Although sequence determination of linear peptides can be routinely achieved by mass spectrometry [4][5][6], sequencing of cyclic peptides is complicated. There have been reports on sequencing of cyclic peptides by fast atom bombardment (FAB) [7][8][9][10][11][12], Fourier transform ion cyclotron resonance (FTICR) [13], triple quadrupole [14], and ion trap [15][16][17][18] mass spectrometry, and reviews [19,20]. However, studies in most of the reports used known cyclic peptides to develop sequencing methodologies [8-10, 12-15, 17], while only a few publications reported sequencing of unknown cyclic peptides [11,[21][22][23].…”