Preferential cleavage of SS and CS bonds in electron detachment dissociation and infrared multiphoton dissociation of disulfide-linked peptide anions

Infrared multiphoton dissociation (IRMPD) is a vibrational excitation tandem mass spectrometric fragmentation method valuable for sequencing of oligonucleotides. For oligodeoxynucleotides, typical product ions correspond to sequence-specific 5′ ( a-base) and their complementary 3′ w-type ions from carbon–oxygen bond cleavage at the 3′ position of the deoxyribose from which a nucleobase is lost. Such fragmentation patterns are also observed in collision activated dissociation (CAD). The CAD oligodeoxynucleotide fragmentation mechanism has been characterized in detail. By contrast, fragmentation schemes in IRMPD have not been rigorously established. In this paper, we apply, for the first time, Fourier transform ion cyclotron double resonance (DR) experiments to characterize IRMPD fragmentation pathways of oligodeoxynucleotide anions. Our results suggest that neutral base loss precedes backbone fragmentation but that T-rich oligodeoxynucleotides fragment via a different mechanism, similar to the mechanisms proposed for CAD. We also extend the DR approach to characterize intermediates in electron detachment dissociation of hexamer oligodeoxynucleotides. Here, we found that charge reduced radical precursor ions constitute major intermediates for dT6, d(GCATAC) and d(GCATGC). Furthermore, ( a/ z–T) ions ( z ions correspond to C–O bond cleavage on the other side of a backbone phosphate group as compared to the formation of a ions) mainly originate from secondary fragmentation of a/ z radical ions for the oligodeoxynucleotide dT6.

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Electron Capture Dissociation, Electron Detachment Dissociation and Infrared Multiphoton Dissociation of Sucrose Octasulfate

European Journal of Mass Spectrometry ◽

10.1255/ejms.951 ◽

2009 ◽

Vol 15 (2) ◽

pp. 275-281 ◽

Cited By ~ 17

Author(s):

Jeremy J. Wolff ◽

Tatiana N. Laremore ◽

Franklin E. Leach ◽

Robert J. Linhardt ◽

I. Jonathan Amster

Keyword(s):

Mass Spectrometry ◽

Electron Capture ◽

Electron Capture Dissociation ◽

Vibrational Excitation ◽

Infrared Multiphoton Dissociation ◽

Electron Detachment Dissociation ◽

Electron Detachment ◽

Sucrose Octasulfate ◽

Product Ions ◽

Multiphoton Dissociation

The structural analysis of sulfated carbohydrates such as glycosaminoglycans (GAGs) has been a long-standing challenge for the field of mass spectrometry. The dissociation of sulfated carbohydrates by collisionally-activated dissociation (CAD) or infrared multiphoton dissociation (IRMPD), which activate ions via vibrational excitation, typically result in few cleavages and abundant SO3 loss for highly sulfated GAGs such as heparin and heparan sulfate, hampering efforts to determine sites of modification. The recent application of electron activation techniques, specifically electron capture dissociation (ECD) and electron detachment dissociation (EDD), provides a marked improvement for the mass spectrometry characterization of GAGs. In this work, we compare ECD, EDD and IRMPD for the dissociation of the highly sulfated carbohydrate sucrose octasulfate (SOS). Both positive and negative multiply-charged ions are investigated. ECD, EDD and IRMPD of SOS produce abundant and reproducible fragmentation. The product ions produced by ECD are quite different than those produced by IRMPD of SOS positive ions, suggesting different dissociation mechanisms as a result of electronic versus vibrational excitation. The product ions produced by EDD and IRMPD of SOS negative ions also differ from each other. Evidence for SO3 rearrangement exists in the negative ion IRMPD data, complicating the assignment of product ions.

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