Unveiling the presence of O-glycosylation in different glycoproteins present in chicken egg white

Chicken egg white contains hundreds of proteins that are widely used in the food, biological and pharmaceutical industries. Glycosylation provides additional structural diversity to the already specialized proteins. The array of glycans on protein surfaces and different glycosylation sites provide sophisticated structures essentials for the multiple functions that glycoproteins assume. Different types of analysis have been performed to determine N-glycosylation in chicken egg white. In different studies, up to 19 N-glycoproteins have been characterized. However, regarding O-glycosylation, there is insufficient knowledge of their structures and abundances. In fact, only ovomucin, a major component of chicken egg white, has been described as bearing O-glycans that consist of 2–6 sugar residues carrying sialic acid and/or sulfate groups. In the present work, the use of a reductive β-elimination reaction followed by a HPAEC-PAD analysis, showed released oligosaccharides suggesting the presence of different O-glycoproteins. Getting deeper into chicken egg white O-glycoproteomics, a nanoHPLC-ESI-Orbitrap-HCD analysis was performed and two different software tools were employed. Under these conditions, at least seven different O-glycosylated proteins were described. In addition, O–glycosylation of isolated ovalbumin was characterized for the first time and in a BEMAD analysis of the isolated glycoprotein, three O-glycosites were detected. Taking into account that glycosylation has been involved in the structure and properties of chicken egg white proteins such as allergenicity, antibacterial action and embryo protection, attention must be paid to explore new properties of this heterogeneous modification in relation to both the food and biopharmaceutical industries.