How are glycoproteins described?
A. Covalently bound sugars are to be handled as HET groups with LINK records to define the points of attachment. Individual sugars will have individual residue numbers. A polysaccharide with a chain length of 2 or greater is treated as a polymer, otherwise it is treated as a ligand or a modification. For covalently bound polysaccharide polymers, the entire attached polysaccharide will have a unique chain ID but will have no SEQRES records. The residue(s) to which the polysaccharide is attached are assigned standard residue names. The modification is further described in MODRES/HET/HETNAM/FORMUL and CONNECT records. Example: Covalently bound polymeric sugar from PDB 1EBV: In this example the protein is glycosylated at ASN 144. Since this polysaccharide in this example has two or more sugars, it is considered a polymer chain. The ASN retains its original name and the modification is described with MODRES/HET/HETNAM/FORMUL/CONNECT records. The point of attachment is defined in LINK record
