BOLD — A biological O‐linked glycan database

Glycans can be O‐linked to proteins via the hydroxyl group of serine, threonine, tyrosine, hydroxylysine or hydroxyproline. Sometimes the glycan is O‐linked to the hydroxyl group via a phosphodiester bond. The core monosaccharide residue may be N‐acetylgalactosamine, N‐acetylglucosamine, galactose, glucose, fucose, mannose, xylose or arabinose. These O‐linked glycans can remain as a monosaccharide, but often a complex structure is built up by stepwise addition of monosaccharides. Monosaccharides known to be added include galactose, N‐acetylglucosamine, fucose, N‐acetylneuraminic acid, N‐glycolylneuraminic acid and 2‐keto‐3‐deoxynonulosonic acid. O‐linked glycans can also contain sulfate and phosphate residues. This leads to the possibility of the existence of numerous O‐glycan structures. The biological O‐linked database (BOLD) is a relational database that contains information on O‐linked glycan structures, their biological sources (with a link to the SWISS‐PROT protein database), the references in which the glycan was described (with a link to MEDLINE), and the methods used to determine the glycan structure. The database provides a valuable resource for glycobiology researchers interested in O‐linked oligosaccharide structures that have been previously described on proteins from different species and tissues.