Chondroitin sulfate
Attachment of the GAG chain begins with four monosaccharides in a fixed pattern: Xyl - Gal - Gal - GlcA.  Each sugar is attached by a specific enzyme, allowing for multiple levels of control over GAG synthesis. Xylose begins to be attached to proteins in the endoplasmic reticulum, while the rest of the sugars are attached in the Golgi apparatus.