A glycoprotein is a protein that contains one or more covalently attached carbohydrates (glycans).
Glycoproteins are a class of proteins distinguished by the presence of oligosaccharide chains (glycans) attached to amino acid side chains. This attachment process is called glycosylation. Glycans can also attach to lipids, forming glycolipids.
Key Characteristics of Glycoproteins:
- Composition: Glycoproteins consist of a protein component and a carbohydrate component (glycan).
- Glycosylation: The addition of glycans to the protein occurs through glycosylation, a crucial post-translational modification.
- Location: Glycoproteins are commonly found on the cell surface, in the extracellular matrix, and in blood.
- Functions: They play diverse roles in biological processes, including cell-cell recognition, immune response, protein folding, and signaling.
Examples of Glycoproteins:
- Antibodies (Immunoglobulins): Involved in the immune response.
- Mucins: Found in mucus, providing lubrication and protection.
- Some hormones (e.g., Glycoprotein hormones like FSH and LH): Play a role in signaling.
- Cell Surface Receptors: Involved in cell communication and signaling.
Glycosylation Types:
Glycans attach to proteins through either:
- N-linked glycosylation: The glycan is attached to the nitrogen atom of an asparagine (Asn) residue.
- O-linked glycosylation: The glycan is attached to the oxygen atom of a serine (Ser) or threonine (Thr) residue.
Glycoproteins are vital for the structure, function, and interactions of cells and organisms.
