Glycoproteins
Overview
Glycoproteins are proteins that have oligosaccharides (chains of sugars) covalently attached to their polypeptide backbones. This type of post-translational modification is crucial for the protein's function. Glycoproteins play a wide variety of roles in biological systems, including cell-cell interaction, immune response, and protein folding more.
Structure
The structure of a glycoprotein is determined by the protein to which the sugars are attached and the specific sugars involved. The oligosaccharides can be attached to the protein in two ways: N-linked, where the sugar is attached to a nitrogen atom in an asparagine amino acid residue, or O-linked, where the sugar is attached to the oxygen atom of a serine or threonine amino acid residue more.
Functions
Glycoproteins perform a wide variety of functions in the body. They are involved in immune response, where they serve as antigens and antibodies. They also play a role in cell-cell interaction, acting as adhesion molecules that allow cells to stick to each other or to the extracellular matrix. In addition, glycoproteins are involved in protein folding, helping to ensure that proteins assume the correct three-dimensional shape more.
Biosynthesis
The biosynthesis of glycoproteins involves the addition of a sugar chain to a protein. This process, known as glycosylation, occurs in the endoplasmic reticulum and Golgi apparatus of the cell. The specific sequence of sugars in the chain and the location of the chain on the protein are determined by enzymes in these organelles more.
Role in Disease
Glycoproteins are involved in a number of diseases. For example, mutations in the genes that code for glycoproteins or the enzymes that add the sugar chains can lead to diseases such as congenital disorders of glycosylation. In addition, some viruses, including HIV and influenza, use glycoproteins on their surface to enter host cells more.