A subclass of protein in which the carbohydrate units are polysaccharides that contain amino sugars. The protein is glycosylated by one or more (up to about 100) glycosaminoglycans [linear polymers of up to about 200 repeating disaccharide units that consist of a hexosamine (ᴅ-glucosamine or ᴅ-galactosamine) alternating with a uronic acid (ᴅ-glucuronic or ʟ-iduronic) or a neutral sugar (ᴅ-galactose)].