Glycobiology

Glycobiology is the study of the structure, biosynthesis, and function of glycans—carbohydrate chains attached to proteins and lipids—and of the enzymes that build and remodel them. Glycans occur as N-linked and O-linked oligosaccharides on glycoproteins, as glycosaminoglycans in proteoglycans, and as glycolipids on membranes. They contribute to protein folding and stability, cellular trafficking, and a wide range of biological processes, including cell signaling, immune recognition, development, and host-pathogen interactions.

Biosynthesis takes place mainly in the secretory pathway. N-linked glycosylation begins in the endoplasmic reticulum with a preassembled oligosaccharide that is transferred to asparagine sites, followed by trimming and elaboration in the Golgi to yield high-mannose, hybrid, or complex structures. O-linked glycosylation occurs in the Golgi on serine or threonine residues, with extensive diversification. Glycans are built and remodeled by glycosyltransferases and glycosidases using donor sugars such as UDP-GlcNAc, GDP-mannose, and CMP-sialic acid.

Functional roles and interactions include mediation of receptor binding, cell adhesion, and immune recognition. Glycan-binding proteins such as lectins and galectins interpret glycan structures and influence signaling and trafficking. In the extracellular matrix, glycosaminoglycans like heparan sulfate and chondroitin sulfate modulate growth factor signaling and provide structural support.

Medical and biotechnological relevance is broad. Defects in glycosylation cause congenital disorders of glycosylation; aberrant glycosylation is associated with cancer and inflammation. In biopharmaceuticals, controlling antibody and enzyme glycosylation can affect efficacy and half-life. Glycobiology relies on analytical methods such as mass spectrometry, NMR, and lectin-based assays to profile glycan structures.