Hyaluronan (HA) is a polysaccharide composed of repeating GlcNAcβ(1 → 4)- GlcUAβ(1 → 3) disaccharide units. This polysaccharide has a molecular mass ranging from 103 to 107 Da, depending on the tissue source and physiological conditions. Three members of the HA synthase family, HAS1, HAS2 and HAS3, have been thus far identified in a wide variety of vertebrates. Sequence analysis has shown that all HAS proteins are composed of multiple membrane-spanning regions and have large cytoplasmic loops. The HAS proteins also possess a DXD motif that is common in the glycosyltransferases of many organisms, and a QXXRW motif conserved in cellulose and chitin synthases. Each HAS isoform differs in enzymatic properties such as stability, substrate kinetics, and rate of sugar chain elongation, and may thus synthesize distinct forms of HA. The HAS1 and HAS3 synthesize HA with an estimated molecular mass of 2 × 105 to 2 × 106 Da, whereas very large molecules of more than 2 × 106 Da are synthesized by HAS2. The HAS genes also show temporally and spatially distinct expression patterns.
KeywordsDistinct Expression Pattern Chitin Synthases Disaccharide Unit Hyaluronan Synthases Crude Membrane Fraction
- Itano N, Sawai T, Yoshida M, Lenas P, Yamada Y, Imagawa M, Shinomura T, Hamaguchi M, Yoshida Y, Ohnuki Y, Miyauchi S, Spicer AP, McDonald JA, and Kimata K (1999) Three isoforms of mammalian hyaluronan synthases have distinct enzymatic properties. J Biol Chem 274:25085–25092PubMedCrossRefGoogle Scholar