The third chains of living organisms—a trail of glycobiology that started from the third floor of building 4 in NIH

Application of a finger-printing method to the analysis of human milk oligosaccharides led to the finding that several oligosaccharides were missing in the milk of non-secretor or Lewis-negative individuals. This finding helped us in opening the door of elucidating the enzymatic basis of blood types in human. Based on these successful studies, a strategy to establish reliable techniques to elucidate the structures and functions of the N-linked sugar chains of glycoproteins was devised. It was to contrive enzymatic and chemical means to release quantitatively the N-linked sugar chains as oligosaccharides, and finger-print them by using appropriate methods to demonstrate the sugar pattern of a glycoprotein. These methods enabled us to determine that the N-linked sugar chains of glycoproteins can be classified into three subgroups: high mannose-type, complex-type, and hybrid-type. By comparative studies of the sugar patterns of a glycoprotein produced by different organs and different animals, occurrences of organ- and species-specific glycosylation were found in many glycoproteins. By comparative studies of the glycosylation patterns of the subunits constructing human chorionic gonadotropin and other glycoproteins, occurrence of site-directed N-glycosylation was also found, indicating that the processing and maturation of the N-linked sugar chains of a glycoprotein might be controlled by the structure of polypeptide moiety. Furthermore, these methods enabled us to elucidate the structural alteration of the sugar chains of a glycoprotein induced by diseased state of the producing cells, such as rheumatoid arthritis and malignancy. Recent studies of glycoproteins in the brain-nervous system through aging revealed that N-glycosylation of P0 in the rat spinal cord is induced by aging. Therefore, glycobiology is expanding tremendously into fields such as pathological and gerontological research.