Electron detachment dissociation of dermatan sulfate oligosaccharides

Abstract

The structural characterization of glycosaminoglycans (GAG) oligosaccharides has been a long-standing challenge in the field of mass spectrometry. In this work, we present the application of electron detachment dissociation (EDD) Fourier transform mass spectrometry to the analysis of dermatan sulfate (DS) oligosaccharides up to 10 residues long. The EDD mass spectra of DS oligosaccharides were compared with their infrared multiphoton dissociation (IRMPD) mass spectra. EDD produces more abundant fragmentation than IRMPD with far less loss of SO3 from labile sulfate modifications. EDD cleaves all glycosidic bonds, yielding both conventional glycosidic bond fragmentation as well as satellite peaks resulting from the additional loss of 1 or 2 hydrogen atoms. EDD also yields more cross-ring fragmentation than IRMPD. For EDD, abundant cross-ring fragmentation in the form of A- and X-ions is observed, with 1,5Xn cleavages occurring for all IdoA residues and many of the GalNAc4S residues, except at the reducing and nonreducing ends. In contrast, IRMPD produces only A-type cross-ring fragmentation for long oligosaccharides (dp6-dp10). As all the structurally informative fragment ions observed by IRMPD appear as a subset of the peaks found in the EDD mass spectrum, EDD shows great potential for the characterization of GAG oligosaccharides using a single tandem mass spectrometry experiment.

Figure 1

MS/MS of [M-2H]²⁻ precursor ion DS dp4, 1, with (A) EDD and (B) IRMPD. Insets; product ions observed by the fragmentation methods. The charge reduced species in the EDD mass spectrum is indicated with a ▼ over the peak label.

Figure 2

A new fragmentation annotation scheme for showing the products of EDD and IRMPD, applied to the [M-2H]²⁻ precursor ion of 1.

Figure 3

EDD mass spectrum of the [M-3H]³⁻ precursor ion of DS dp6, 2. Inset: Observed product ions from the EDD and IRMPD MS/MS data of 2 combined and annotated using the scheme presented in Figure 2.

Figure 4

EDD mass spectrum of the [M-4H]⁴⁻ precursor ion of DS dp8, 3. The mass scale was divided into three regions for clarity. (A) m/z 155–460, (B) m/z 455–650, and (C) m/z 645–1100. Inset: observed product ions from the EDD and IRMPD MS/MS data of 3 combined and annotated using the scheme presented in Figure 2. The charge reduced species is indicated with a ▼ over the peak label.

Figure 5

EDD mass spectrum of the [M-5H]⁵⁻ precursor ion of DS dp10, 4. The mass scale was divided into three different regions for clarity. (A) m/z 155–460, (B) m/z 455–650, and (C) m/z 645–1100. The charge reduced species is indicated with a ▼ over the peak label.

Figure 6

Observed product ions from the EDD and IRMPD MS/MS data of DS dp10, 4, combined and annotated using the scheme presented in Figure 2.

Scheme 1

Scheme 2

Structures