O-Glycoproteomic analysis of engineered heavily glycosylated fusion proteins using nanoHILIC-MS

Recombinant protein engineering design affects therapeutic properties including protein efficacy, safety, and immunogenicity. Importantly, glycosylation modulates glycoprotein therapeutic pharmacokinetics, pharmacodynamics, and effector functions. Furthermore, the development of fusion proteins requires in-depth characterization of the protein integrity and its glycosylation to evaluate their critical quality attributes. Fc-fusion proteins can be modified by complex glycosylation on the active peptide, the fragment crystallizable (Fc) domain, and the linker peptides. Moreover, the type of glycosylation and the glycan distribution at a given glycosite depend on the host cell line and the expression system conditions that significantly impact safety and efficacy. Because of the inherent heterogeneity of glycosylation, it is necessary to assign glycan structural detail for glycoprotein quality control. Using conventional reversed-phase LC-MS methods, the different glycoforms at a given glycosite elute over a narrow retention time window, and glycopeptide ionization is suppressed by co-eluting non-modified peptides. To overcome this drawback, we used nanoHILIC-MS to characterize the complex glycosylation of UTI-Fc, a fusion protein that greatly increases the half-life of ulinastatin. By this methodology, we identified and characterized ulinastatin glycopeptides at the Fc domain and linker peptide. The results described herein demonstrate the advantages of nanoHILIC-MS to elucidate glycan features on glycotherapeutics that fail to be detected using traditional reversed-phase glycoproteomics.