# Characteristic Fragmentation Behavior of Linear and Cyclic O-Linked Glycopeptides and Their Peptide Skeletons in MALDI-TOF/TOF MS

## TL;DR

This paper studies how linear and cyclic O-linked glycopeptides fragment in MALDI-TOF/TOF MS, helping identify their structures and functions.

## Contribution

The study reveals novel fragmentation patterns of cyclized and linear O-linked glycopeptides and their peptide skeletons.

## Key findings

- Fragmentation patterns differ between linear and cyclic glycopeptides.
- Glycan presence and serine substitution affect fragmentation behavior.
- Findings aid in predicting peptide structures and identifying active glycopeptides.

## Abstract

Understanding characteristic post-source decay (PSD) fragmentation patterns in tandem mass spectrometry (MS/MS) is important for the identification of target molecules. In this study, we explored the characteristic PSD patterns associated with O-linked glycopeptides and their cyclization using the MALDI-TOF/TOF MS analysis of linear and cyclic antifreeze glycoproteins. We performed a comparative analysis of the proton and sodium adduct ions of the peptide backbones of antifreeze glycoproteins, which have a simple repeating sequence, shedding light on the characteristics of the fragmentation of the threonine side chain and that of its cyclized form. Furthermore, the presence or absence of a glycan on the threonine side chain and its substitution with serine caused changes in its fragmentation. These findings are expected to contribute to the prediction of three-dimensional peptide structures and the search for physiologically active O-linked glycopeptides and cyclic (glyco)peptides.