What is the structure of proteoglycans?

Proteoglycans are composed of a core protein and one or more covalently attached sulfated glycosaminoglycan chains. The core protein contains serine and threonine residues, and acts as a point of attachment for glycosaminoglycans. The GAGs are linear polysaccharides consisting of an amino sugar (either GlcNAc or GalNAc) and a uronic acid (IdoA and GlcA).  The glycosaminoglycans attach to the core protein in a perpendicular manner and create a brush-like structure. Most GAGs are attached to the core protein through tetrasaccharide links made of glucuronic acid, two galactose molecules, and a xylose sugar through glycosidic bonds.Proteoglycans act more as polysaccharides rather than as proteins, as 95% of its weight is composed of sulfated glycosaminoglycan.