Glykans

Glykans is a term used in some scientific contexts to refer to glycans, a broad class of carbohydrate polymers that form part of many biological molecules. Glycans are composed of monosaccharide units linked by glycosidic bonds and exhibit extensive variability in composition, linkage positions, and branching. They can be free polysaccharides or covalently attached to proteins or lipids as glycoconjugates, where they influence structure and function of the molecules they are attached to.

Classification includes N-linked glycans attached to asparagine residues in proteins, O-linked glycans attached to serine or threonine, and glycosaminoglycans such as heparan sulfate, chondroitin sulfate, and hyaluronic acid that form linear repeating disaccharide units. Glycans can also be part of proteoglycans or glycoproteins, where they modulate stability, solubility, and recognition by other molecules.

Biogenesis: In eukaryotes, glycan assembly begins in the endoplasmic reticulum and continues in the Golgi apparatus. Enzymes called glycosyltransferases add sugars from activated nucleotide donors, while glycosidases trim or remodel chains. The final structures depend on enzyme expression, substrate availability, and trafficking within the cell.

Functions: Glycans influence protein folding and quality control in the ER, determine trafficking routes, mediate cell–cell and cell–matrix interactions, and participate in immune recognition. They also regulate signaling by growth factors and interact with carbohydrate-binding proteins (lectins) to form dynamic networks on cell surfaces and extracellular matrices.

Clinical relevance: Aberrant glycosylation is associated with cancer, autoimmune diseases, infectious diseases, and congenital disorders of glycosylation. Glycan profiles serve as biomarkers and, in some cases, as therapeutic targets or vaccines.