Why glycan characterization is critical in biopharmaceutical development

Glycosylation is one of the more structurally diverse and biologically impactful PTMs in protein therapeutics. Both N‑linked and O‑linked glycans influence protein folding, stability, and biological activity. Given these effects on biotherapeutics, glycosylation is a closely monitored critical quality attribute (CQA). Comprehensive and site‑specific characterization of glycosylation is essential for informed decision‑making throughout drug discovery and development.

However, the inherent heterogeneity of glycans and the labile nature of glycan–peptide linkages make confident characterization challenging using conventional collision‑based fragmentation alone.

Limitations of CID‑only approaches for glycopeptide analysis

Traditional collision‑induced dissociation (CID) preferentially fragments glycan moieties, often resulting in loss of the glycan structure from peptide backbone fragments. This behavior can limit the ability to confidently localize glycosylation sites or distinguish positional isomers, particularly for O‑linked glycosylation, where no consensus sequence exists. As a result, CID‑only workflows may provide incomplete or ambiguous information for glycan characterization in complex biotherapeutics.

The EAD advantage for glycan characterization

Electron-activated dissociation (EAD) addresses these limitations by enabling electron‑driven backbone fragmentation while preserving labile glycan structures on the fragment ions. When applied to glycopeptides, EAD produces peptide backbone fragments that retain attached glycans, supporting unambiguous site localization and confident identification of glycoforms.

Key advantages of EAD for glycan analysis include:

• Retention of intact glycan structures on fragment ions, enabling accurate site localization
• Differentiation of positional isomers of O‑linked glycopeptides
• High‑quality MS/MS spectra suitable for automated data analysis
• Compatibility with fast, data‑dependent acquisition workflows

Comprehensive characterization of O‑linked glycosylation

O‑linked glycosylation presents a particular analytical challenge due to its structural diversity and lack of a consensus sequence motif. In the case of etanercept, a highly glycosylated fusion protein containing multiple O‑glycosylation sites, EAD‑based glycopeptide analysis enables confident identification and unambiguous localization of O‑linked glycans. (1)  By preserving glycan structures on peptide backbone fragments, EAD further supports differentiation of positional isomers of O‑glycopeptides, which is difficult to achieve using CID alone.

Site‑specific N‑linked glycan profiling on complex fusion proteins

For fusion proteins such as aflibercept, which contain multiple N‑linked glycosylation sites with extensive microheterogeneity, site‑specific glycan profiling is essential to understand glycan occupancy and distribution. EAD‑enabled peptide mapping workflows provide accurate localization of N‑linked glycans and confident peptide identification by generating extensive backbone fragmentation while retaining glycan modifications. Automated data processing using Biologics Explorer software further enables efficient interpretation of complex glycopeptide datasets.

Streamlined data analysis with Biologics Explorer software

EAD‑enabled glycan characterization workflows are supported by Biologics Explorer software, which provides optimized templates for peptide mapping and PTM analysis. Glycopeptide fragments are automatically identified, mapped, and annotated, with results presented in an integrated review environment that includes sequence coverage maps and MS/MS spectral views. This workflow‑driven approach reduces manual interpretation and supports reproducible, confident glycan characterization across development stages.

Where EAD‑enabled glycan workflows fit in development

EAD‑based glycan characterization workflows support:

• Site‑specific localization of N‑ and O‑linked glycans
• Differentiation of glycopeptide positional isomers
• Detection of low‑abundance glycan‑related PQAs
• Confident characterization of glycosylation in complex modalities

By combining information‑rich fragmentation, enhanced sensitivity, and automated data analysis, EAD on the ZenoTOF systems provides a practical and powerful solution for confident glycan characterization in modern biopharmaceutical development.

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Read the technical notes:

1. Comprehensive characterization of O-linked glycosylation in etanercept by electron activated dissociation (EAD)
2. Site-specific N-linked glycan profiling on the fusion protein aflibercept using a novel fragmentation technique

Watch a webinar:   Combining orthogonal glycan analysis techniques for a deeper understanding of a tri-specific protein

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