Table 1.
Glycoaminoglycan Repeating Disaccharide Units and Common Skin Proteoglycan Composition
| GAG Repeating Unit Structure | ||||||
| Sugar 2 | ||||||
| Glucuronic Acid | Iduronic Acid | Galactose | ||||
| Sugar 1 | GalNAc | CS | DS | |||
| GlcNAc | HA HS (basic structure) |
KS | ||||
| GlcN | HS (post-modification) | HS (post-modification) | ||||
| Proteoglycan Composition | ||||||
| Proteoglycan | Core Protein kDa | Location | Constituent GAG Chains | |||
| Versican | 72–373 kDa | Extracellular | Multiple chains of CS | |||
| Decorin | 36 kDa | Extracellular | Single chain of CS or DS (mostly DS in skin) | |||
| Biglycan | 38 kDa | Extracellular | 2 chains of DS, may also be 2 chains of CS | |||
| Perlecan | 400–450 kDa | Extracellular | Up to 3 chains HS, may also be CS | |||
| Lumican | 37 kDa | Extracellular | 2–3 chains of KS (KS-I) | |||
| Syndecan family | 22–43 kDa | Transmembrane/extracellular | Multiple CS and HS chains (syndecan isoform dependent) | |||
Notes: Glycosaminoglycan repeating units are composed of an amino sugar (sugar 1), and a uronic sugar (sugar 2). The exception is KS, which has the monosaccharide sugar galactose in place of an uronic sugar. Heparan sulfate is initially comprised of GlcNAc & glucuronic acid repeating units, with N-acetylation/N-sulfation of GlcNAc yielding sections of N-sulfated GlcN which can subsequently be 6-O sulfated, or rarely 3-O sulfated. Some glucuronic acid groups are transformed to iduronic acid, likely determined by different proportions of sulfotransferases & epimerases. Proteoglycans consist of a protein backbone with characteristic constituent GAG chains, and may contain single or multiple GAG chains. Characteristics of prominent proteoglycans in skin shown3.