Hyaluronan Synthase Assay

Abstract

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.