Electron detachment dissociation of glycosaminoglycan tetrasaccharides

Abstract

The first application of electron detachment dissociation (EDD) to carbohydrates is presented. The structural characterization of glycosaminoglycan (GAG) oligosaccharides by mass spectrometry is a longstanding problem because of the lability of these acidic, polysulfated carbohydrates. Doubly-charged negative ions of four GAG tetrasaccharides are examined by EDD, collisionally activated dissociation (CAD), and infrared multiphoton dissociation (IRMPD). EDD is found to produce information-rich mass spectra with both cross ring and glycosidic cleavage product ions. In contrast, most of the product ions produced by CAD and IRMPD result from glycosidic cleavage. EDD shows great potential as a tool for locating the sites of sulfation and other modifications in glycosaminoglycan oligosaccharides.

Figure 1

Fragment ion naming convention used in this paper, adapted from Domon and Costello [37]. Superscripts in cross ring cleavage products refer to the bonds that are broken, which are numbered as shown for the second saccharide from the nonreducing end.

Figure 2

Tandem mass spectra of the [M-2H]²⁻ precursor ion of tetrasaccharide 1, obtained by using (A) EDD, (B) IRMPD, and (C) CAD.

Figure 3

EDD mass spectrum of the [M-2H]²⁻ precursor ion of tetrasaccharide 2. The ^2,4A₃ product in 1 is not observed since it overlaps with the Z₂ product. The ^1,4X₂ product in 1 is not observed since it overlaps with the ^1,5A₃ product. C₂ and Z₂ are not observed since the products overlap with the precursor ion.

Figure 4

EDD mass spectrum of the [M-2H]²⁻ precursor ion of tetrasaccharide 3. The B₂ and Y₂ product ions are not observed as they overlap with the precursor ion.

Figure 5

Tandem mass spectra of the [M-2H]²⁻ precursor ion of tetrasaccharide 4, obtained by using (A) EDD, (B) IRMPD, and (C) CAD.

Scheme 1

Fragmentation observed when sulfated GAGs are irradiated with 19 eV electrons.

Scheme 2

Proposed fragmentation mechanism of 1 to form the C₂-H product ion.

Scheme 3a

Proposed mechanism for H• transfer followed by fragmentation to form the ^3,5A₃ and ^0,2A₃ product ions.

Scheme 3b

Alternative mechanism for H• transfer followed by fragmentation to form the ^3,5A₃ and ^0,2A₃ product ions.

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