Glykoprotein

Glykoprotein, more commonly written glycoprotein, is a protein that contains covalently attached carbohydrate chains, or glycans. The carbohydrate portions are typically linked to the protein by N-linked glycosylation (to asparagine residues) or O-linked glycosylation (to serine or threonine residues). Glycosylation occurs mainly in the endoplasmic reticulum and the Golgi apparatus, where initial attachments are established in the ER and further processing creates a diverse array of glycan structures.

Glycoproteins perform a wide range of roles. They contribute to the stability, solubility, and folding of proteins; participate in cell–cell recognition and signaling through interactions with lectins and receptors; and form protective mucin layers in secretions. They are abundant on cell surfaces as receptors or ligands and are central components of the immune system, including antibodies and MHC molecules, as well as numerous extracellular proteins such as hormones and enzymes. Viral and other pathogen glycoproteins use glycosylation for attachment and immune evasion, often described as a glycan shield.

In biomedicine, many therapeutic proteins are glycoproteins, and their glycosylation pattern influences activity, distribution, immunogenicity, and half-life. Researchers use glycoengineering to tailor these properties. Analytical work on glycoproteins focuses on characterizing glycosylation patterns, which can be heterogeneous even within a single protein, complicating manufacture and quality control.