glycocalyx

Glycocalyx refers to a carbohydrate-rich layer that coats the exterior of the plasma membrane in many animal cells and in some microorganisms. It is formed from glycoproteins, proteoglycans, glycolipids, and associated polysaccharides that extend from the cell surface into the surrounding milieu. The composition and thickness vary among cell types and contexts, influencing how the cell interacts with its environment.

Key components include membrane-anchored glycoproteins such as mucins, proteoglycans bearing glycosaminoglycans (GAGs) like heparan sulfate and chondroitin sulfate, and glycolipids. These molecules create a hydrated, gel-like layer that is negatively charged and highly dynamic, continually remodeled by the cell and extracellular enzymes.

Functions of the glycocalyx include protection against mechanical and chemical damage, lubrication, and shaping the surface properties of the cell. It mediates cell–cell and cell–substrate interactions, influences receptor accessibility and signaling, and plays roles in immune recognition, fertilization, and pathogen binding. In blood vessels, the endothelial glycocalyx contributes to barrier function, modulates vascular permeability, and participates in mechanotransduction under shear flow.

Disruption or alteration of the glycocalyx has been implicated in various diseases and conditions, including diabetes, sepsis, and inflammatory disorders. Loss or thinning of the layer can affect barrier function and cell signaling. Because of its surface accessibility and involvement in multiple processes, the glycocalyx is an area of active research for diagnostics and therapeutic strategies.