# Mechanistic study on the sulfate migration in glycosaminoglycans during MS fragmentation

## TL;DR

This study investigates how sulfate groups move during mass spectrometry in glycosaminoglycans, leading to isomeric fragments that complicate structural analysis.

## Contribution

The study reveals a multi-step mechanism of sulfate migration in heparin sulfate disaccharides during MS fragmentation.

## Key findings

- Sulfate groups migrate from the non-reducing to the reducing end of the sugar during MS.
- Migration results in sulfate attachment at the 6O- or 3O-position of GlcNAc.
- The migration mechanism involves multiple steps, starting with sulfate shifting from iduronic acid to 6O-position of GlcNAc.

## Abstract

Glycosaminoglycans use positional sulfation to encode binding specificity onto its sequence. Understanding these sulfation patterns constitute a major challenge. Previous studies hinted that sulfate groups can migrate along glycans during collision-induced dissociation in mass spectrometry (MS) experiments, forming isomeric fragments that can lead to incorrect structural assignments. We use ion-mobility – mass spectrometry to investigate the mechanism of this phenomenon in heparin sulfate disaccharides. The sulfate group migrates from the non-reducing to reducing end of the sugar, and the degree of migration does not depend on the structure of the label. The migration product has a sulfate group attached to either 6O- or 3O-position of GlcNAc, and the migration mechanism consists of multiple steps, with the sulfate group first shifting from the iduronic acid to the 6O-position of GlcNAc, and next to the 3O-position. The presented data offer insight into the complexity and unpredictability of sulfated sugar fragmentation in tandem MS and extensive investigations is required to determine whether this represents a singular case or a general phenomenon characteristic of deprotonated sulfated glycans.

Glycosaminoglycans encode binding specificity through positional sulfation, but understanding these patterns is challenging due to sulfate migration during mass spectrometry (MS). Here, the authors use ion-mobility MS to investigate the isomerization reaction of heparin sulfate disaccharides in the gas phase, providing insights into the resulting isomeric products and potential rearrangement mechanisms of sulfate migration.