Glycan–protein linkages reported in nature. (Updated and redrawn, with permission of Oxford University Press, from Spiro RG. 2002. Glycobiology 12: 43R–56R.) Diagrammatic representation of six distinct types of sugar-peptide bonds that have been identified in nature, to date. (See Online Appendix 1B for full names of monosaccharides.) (Hyl) Hydroxylysine; (Hyp) hydroxyproline; (C-term) carboxy-terminal amino acid residue. Glypiation is the process by which a glycosylphosphatidylinositol (GPI) anchor is added to a protein. For other details, including anomeric linkages, please see the Spiro (2002) review cited above.