Electron Capture Dissociation of Oligosaccharides Ionized with Alkali, Alkaline Earth, and Transition Metals

Abstract

We extend the application of electron capture dissociation (ECD) (which requires at least two charges) to oligosaccharides without basic functionalities by utilizing alkali, alkaline earth, and transition metals (Na+, K+, Ca2+, Ba2+, Mg2+, Mn2+, Co2+, and Zn2+) as charge carriers in electrospray ionization. Both linear and branched oligosaccharides were examined, including maltoheptoase, p-lacto-N-hexaose, and an N-linked glycan from human alpha1-acid glycoprotein. For comparison, infrared multiphoton dissociation (IRMPD) was also applied to all oligosaccharide species. We show that, for certain metal-adducted oligosaccharides, particularly maltoheptaose, cross-ring cleavage, which can provide saccharide linkage information, is the dominant fragmentation pathway in ECD. By contrast, glycosidic cleavages dominate in IRMPD although cross-ring fragmentation was also observed to varying degrees depending on metal ion type. The branched N-linked glycan did not fragment as easily following ECD compared to the linear oligosaccharides, presumably due to intramolecular noncovalent interactions. However, this limitation was partially overcome with a combined ECD/IRMPD approach (activated ion ECD). For all metal-adducted oligosaccharides, complementary structural information was obtained with ECD as compared to IRMPD. Our results demonstrate that ECD of metal-adducted oligosaccharides is a valuable tool for structural characterization of oligosaccharides.

Electron detachment dissociation of neutral and sialylated oligosaccharides

“…EDD of this branched glycan demonstrates that EDD fragmentation efficiency does not seem to be affected by oligosaccharide branching. We have shown that ECD of larger, branched oligosaccharides requires ion activation (presumably due to secondary structure) to fragment efficiently [31]. However, electron energies used for EDD (20 -30 eV in the current experiments) are much higher than those typically used for ECD (Ͻ1 eV).…”

“…Although most modern mass analyzers use lowenergy dissociation techniques such as low-energy CAD, several alternative fragmentation techniques have been developed and applied to oligosaccharides, including high-energy CAD [25][26][27], IRMPD [28,29], electron capture dissociation (ECD) [30,31], electron detachment dissociation (EDD) [32,33], and 157-nm photodissociation [34]. In particular, the use of ionelectron reactions for biomolecular structural characterization is rapidly expanding.…”

“…ECD has been applied to protonated chitooligosaccharides, which yielded primarily glycosidic cleavages corresponding to B-and C-type ions [30], and recently to permethylated oligosaccharides [44]. We have demonstrated that ECD of oligosaccharides ionized with divalent metal ions can result in additional fragmentation not observed following vibrational excitation [31].…”

Characterization of phosphate-containing metabolites by calcium adduction and electron capture dissociation

“…Another alternative approach may be to allow positive-ion mode analysis. We have shown that divalent metal ions can be used as efficient charge carriers for sulfated peptides [36] and for oligosaccharides [37]. In both cases, utilization of a divalent metal allowed formation of doubly charged cations, which are required for ECD.…”

“…In our previous work [36,37,48], Ca 2ϩ was found to be a suitable divalent metal due to its propensity to form abundant complexes with molecules of interest and the analytical utility of the corresponding ECD spectra. In the present work, we also compare ECD with sustained off-resonance irradiation (SORI) CAD [49] of calcium-adducted phosphate-containing metabolites.…”