Initial polymer chains and their biosynthesis

Hyaluronan p-GlcA/ -(1 3)-p-GlcNAc/ -(l ). The biosynthesis proceeds, apparently without any primer requirement (unlike heparan and chondroitin), by stepwise addition of UDPGlcA and UDPGlcNAc, from the non-reducing end. As with heparan, the synthetases are single polypeptides which catalyse both transfer reactions. 

Keratan p-Gal/ -(l )-p-GalNAc/ -(l- 3). Oligosaccharide chains (20-50 residues) derived from this polymer form part of biantennary N-linked glycoproteins (keratin sulfate type I, such as corneal keratan sulfate) and shorter stretches, fucosylated, as part of O-linked glycoproteins (keratin sulfate type II, such as 

The heparan, chondroitin and hyaluronan synthetases, although one polypeptide chain, have two active sites corresponding to the two glycosyl transfers catalysed. Kinetic studies are technically very difficult, but the point was established in the case of the hyalurononan and chondroitin synthetases by the construction of chimeric proteins. Pasteurella multocida produces both chondroitin and hyaluronan by the action of two-domain single polypeptide synthetases. The chimeric protein from the N-terminal half of the hyaluronan synthetase and the C-terminal half of the chondroitin synthetase produced only 

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Initial polymer chains and their biosynthesis. The four basic repeats are as follows (Figure 4.75) ... 

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