Glycosylation of Proteins in the Golgi Apparatus

Abstract

Oligosaccharides are essential for interactions of cells with their environments. These complex carbohydrates are often found covalently attached to proteins embedded in eukaryotic cell membranes. Protein glycosylation is heterogeneous; this heterogeneity stems from the biosynthesis of these polymers. As proteins destined for secretion or cell‐surface presentation traffic through the endoplasmic reticulum and the Golgi apparatus, they are modified with sugars in a stepwise fashion by enzymes called glycosyltransferases. The differential expression of these enzymes leads to a multiplicity of specific oligosaccharides both among and within cells because not all cells contain all enzymes and because not all substrate proteins will encounter every enzyme. Although myriad oligosaccharides are found attached to proteins, most of these diverse structures can be grouped into several classes of glycans. In this article, we will discuss some of the most common forms of Golgi protein glycosylation: mucin‐type O ‐linked glycosylation, N ‐linked glycosylation, and the formation of glycosaminoglycans. In addition, we will briefly consider some less common, but essential, forms of glycosylation.