Glikany

Glikany, known in English as glycans, are polysaccharides composed of long chains of monosaccharides linked by glycosidic bonds. They are ubiquitous in biology and exhibit great structural diversity, varying in size, composition, and branching. Glikany can be free in solution, or covalently attached to proteins (as in glycoproteins), lipids (as glycosphingolipids), or form proteoglycans when bound to a core protein with attached glycosaminoglycan chains. Major classes include N-glycans and O-glycans, which are carbohydrate moieties covalently linked to nascent proteins, as well as glycosaminoglycans (GAGs), a subgroup of long, often sulfated polysaccharides such as heparan sulfate, chondroitin sulfate, dermatan sulfate, keratan sulfate, and hyaluronic acid.

Biosynthesis occurs primarily in the endoplasmic reticulum and Golgi apparatus, using nucleotide-sugar donors. N-glycans are assembled on a lipid intermediate and transferred en bloc to asparagine residues; O-glycans are built sequentially on serine/threonine residues. GAGs are synthesized by alternating addition of disaccharides in the Golgi and typically undergo sulfation to create highly charged chains.

Functions of glikany include contributing to protein folding quality control, mediating cell-cell and cell-matrix interactions, shaping the extracellular matrix, and modulating signaling pathways via lectin recognition. They also form protective capsules or shields on microbial surfaces and influence immune responses.

Clinically and in research, altered glycosylation patterns are linked to congenital disorders of glycosylation and various diseases including cancer. Glycomics, the study of glycans, seeks to map glycan structures and functions, with applications in biotechnology and medicine, such as engineering antibody glycosylation to tune effector activity.