A cartoon of a proteoglycan complex of connective tissue. Hurler's syndrome is one example of a lysosomal storage disease, caused by loss of a degradative enzyme. Among the O-linked glycans are the blood group substances . Functions Mucins contain large numbers of O-linked saccharides, and protect mucous membranes in the respiratory and GI tracts. Carbohydrate gives an extended conformation to the protein, leading to high viscosity and extensive networks.
Some membrane receptors contain domains that are very rich in O-linked saccharides.
The extended conformations of such regions have been postulated to hold the ligand-binding domain of some receptors out away from the carbohydrate complexes right at the cell surface. The LDL receptor contains a carbohydrate rich domain that may orient the receptor above the cell glycocalyx, increasing the chance of binding the LDL particle. N-linked sugars in glycoproteins. In glycoproteins, carbohydrate chains are attached to the protein. Trimming removes terminal glucose and mannose residues.