Glycome Atlas
molecule
Also known as hyaluronic acid, HA, hyaluronate
GlcA (β1-3) → GlcNAc (repeating unit)
How to read these diagrams (SNFG)
Each shape is a class of sugar and each colour a specific one. Structures read right to left, with the reducing end (the point of attachment) on the right.
Plain-language answer
Hyaluronan is an extremely long, unbranched sugar chain made of the same two-sugar unit repeated thousands of times. Unlike most of the other big sugar chains in the body, it is not attached to a protein and it carries no sulfate groups. It holds a lot of water, which is why it makes tissues and the vessel lining feel soft and cushioned.12
In blood vessels hyaluronan is woven through the glycocalyx and helps the lining hold water, stay slippery, and resist leaking. When the vessel wall is injured, hyaluronan is broken down and released, so it is part of the same shedding process that thins the protective coating during illness.2
Technical detail
Hyaluronan is a non-sulfated, unbranched glycosaminoglycan composed of repeating disaccharides of glucuronic acid linked to N-acetylglucosamine, reaching very high molecular weight and, unlike other glycosaminoglycans, synthesized at the plasma membrane without a protein core, where in the vasculature it becomes enmeshed within the endothelial glycocalyx.12
Hyaluronan consists of a single, unbranched chain of the repeating disaccharide glucuronic acid beta-1,3 N-acetylglucosamine, joined by beta-1,4 linkages, that can extend to millions of daltons. It is unique among glycosaminoglycans in carrying no sulfate groups and in not being covalently attached to a proteoglycan core protein.1
Rather than being assembled in the Golgi and attached to a protein, hyaluronan is synthesized directly at the plasma membrane by hyaluronan synthases and extruded into the extracellular space, where its length and abundant water binding give it distinctive space-filling and hydrating properties.1
In the vessel wall hyaluronan is interwoven with the membrane-bound proteoglycan scaffold and the glycoproteins of the glycocalyx, contributing to the hydrated endothelial surface layer that sets permeability and lubricates blood flow. Enzymatic degradation by hyaluronidase during inflammation releases hyaluronan fragments and participates in the thinning of the layer.2
Human relevance
Loss of hyaluronan from the endothelial glycocalyx accompanies the broader shedding of the layer seen in inflammation and critical illness, and is associated with increased vascular permeability.2
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References