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Glycobiology vol. 11 no. 8 pp. 99R–105R, 2001 MINI REVIEW The history of glycobiology in Japan Akira Kobata University of Tokyo and the Tokyo Metropolitan Institute of Gerontology, 5–18–2 Tsurumaki, Tama-shi, Tokyo 206–0034, Japan Accepted on May 25, 2001 This mini review surveys the major accomplishments in the field of glycoconjugates research in Japan, which were made after World War II. It describes early movements in the field of glycoconjugate research in Japan, development of the new techniques to investigate structures of the sugar chains of glycoconjugates, studies of the functions of the sugar chain moieties, and the political movement in Japan to support the basic research necessary for the development of glycotechnology. As introduced in this short article, important groundwork for glycobiology was made by Japanese researchers. Key words: glycobiology, N-linked sugar chain, O-linked sugar chain, glycoprotein, proteoglycan, glycolipid The early years after World War II On August 15, 1945, World War II was over. Although great chaos reigned across Japan for many years, natural science in the country had slowly but steadily been recovering from paralysis. In the field of carbohydrate research, major development started by the study of “homoglycans,” polysaccharides consisting of only one type of sugar. Jiro Nikuni’s group at Osaka University was actively investigating starch, and Choji Araki and Susumu Hirase at Kyoto Technical University were making progress in the study of galactans purified from agar, which was a specialty of Japan. The study of complex carbohydrates was not prosperous, but some groups had already developed the seeds that would grow into excellent programs. Among them, the strongest group was built by Hajime Masamune at Tohoku University School of Medicine. As a professor in the Department of Medical Chemistry, he was examining pathological and biochemical aspects of the glycoconjugates. He trained many excellent students: Zensaku Yoshizawa, Noboru Hiyama, Keisuke Tsurumi, and Sen-itiroh Hakomori. They were scattered as leaders across several universities in the northeast of Japan and built up the focus on glycoconjugate research. In 1960, Tansuikabutsu Danwakai, a private workshop on carbohydrate research, was organized by Tomoo Miwa (Tokyo College of Education), Torao Ootsuki (Ochanomizu Women’s University), and Susumu Murakami (Saitama University). Although these three leaders were investigating plant © 2001 Oxford University Press carbohydrates and related enzymes, many young researchers of animal glycoconjugates joined in this workshop. By the end of 1960s, several other research cores for the study of glycoconjugates were built in Japan. Tamio Yamakawa (glycolipids), Ikuo Yamashina (glycoproteins), Sakaru Suzuki and Kimiko Anno (proteoglycans), Toshiaki Osawa (lectins), and Fujio Egami (glycosidases) were actively developing their programs. In 1976, the 8th International Carbohydrate Symposium, chaired by Konoshin Onodera, professor at Kyoto University, was held at Kyoto. This afforded a good chance to bring together carbohydrate chemists and biochemists scattered in Japan, and a desire to establish a new society for carbohydrate research ran through the country. In 1978, an official workshop of carbohydrate research (renamed as the Japanese Society of Carbohydrate Research in 1987) was founded by the efforts of Akira Misaki and others, and the first annual meeting was held at Nakanoshima, Osaka. Yoshio Matsushima, professor at Osaka University, was elected as the first president. It was fortunate for carbohydrate researchers in Japan that from the start the society included investigators interested in both homoglycans and glycoconjugates. Methods to analyze the structures of sugar chains Interest in the sugar chains of glycoconjugates had been stimulated in the early 1960s by elucidation of the antigenic determinants of human blood types (Kabat, 1956; Watkins, 1966), and the molecular basis of antigenic conversion of bacteria (Uchida and Robbins, 1963). This research area attracted the interest of many biologists because the development of cell biology in the 1970s suggested that the sugar chains of glycoconjugates might be working as signals in cell to cell recognition. Studies to develop sensitive and reliable methods to analyze the structures of the sugar chains of glycoconjugates have been actively performed in Japan. Methylation analysis reported by Hakomori (1964)) was very useful, because complete methylation of heterosaccharides can be accomplished by a single procedure. The problems of N-methylation of aminosugar residues and the poor recovery of O-methylated N-methylaminosugars by gas chromatography were solved by the successful synthesis of all partially O-methylated 2-N-methylglucosamines and by introduction of OV-17 as a liquid phase (Tai et al., 1975). Many eliminases (Yamagata et al., 1968; Hiyama and Okada, 1975; Oike et al., 1982), exoglycosidases (Iijima and Egami , 1971; Iijima et al., 1971; Kochibe, 1973; Uchida et al., 99R A. Kobata 1974; Arakawa-Ogata et al., 1977; Yoshima et al., 1979; Ichishima et al., 1981; Amano and Kobata, 1986; Kitajima et al., 1994), and endoglycosidases (Kitamikado and Ueno, 1970; Koide and Muramatsu, 1974; Ito et al., 1975; Takasaki and Kobata, 1976a,b; Endo and Kobata, 1976), were found as useful tools for the studies of proteoglycans and glycoproteins. These enzymes were isolated and their substrate specificities were determined by Japanese investigators (Kitamikado and Ueno, 1972; Nishigaki et al., 1974; Arakawa et al., 1974; Fukuda and Matsumura, 1976; Takasaki and Kobata, 1976a,b; Yamashita et al., 1976, 1980b, 1981b; Tai et al., 1977; Fukuda et al., 1978; Mizuochi et al., 1984). Development of hydrazinolysis (Takasaki et al., 1982), radioisotope (Takasaki and Kobata, 1974), and fluorescent taggings (Hase et al., 1986) of the oligosaccharides released by either enzymatic or chemical means, fractionation of oligosaccharides by gel permeation (Yamashita et al., 1982a), highperformance liquid chromatography (Tomiya et al., 1988; Higashi et al., 1990), and affinity chromatography with use of immobilized lectin columns (Ogata et al., 1975) were also developed. By elucidating the binding specificities of many other immobilized lectins, serial lectin column chromatography was established as a very effective method to fractionate and analyze the structures of N-linked sugar chains (Kobata and Yamashita, 1993). Furthermore, application of the frontal analysis (Kasai and Ishii, 1978) to lectin affinity chromatography increased the value of this technique (Okayama et al., 1985). Aminoglycopeptidase (Takahashi, 1977), which was introduced later, was also used as a very effective tool. Glycoproteins Establishment of these reliable analytical methods enabled us to study the structures of the N-linked sugar chains accurately. Accumulation of structural data revealed the structural diversity present in this major group of glycoprotein glycans. Accordingly, finding of the occurrence of the hybrid-type sugar chains (Tai et al., 1976), together with the structural determination of the largest high mannose type sugar chain (Ito et al., 1977), played important roles in the elucidation of an unique biosynthetic pathway of the N-linked sugar chains by Robbins et al. (1977) and Kornfeld’s group (Tabas et al., 1978). Structural heterogeneity in the outer chain moieties of the complex-type sugar chains, including occurrence of the pentaantennary complex-type sugar chains (Yamashita et al., 1982b), was also elucidated. The enzymatic bases for the formation of these structures was revealed by the molecular cloning of the glycosyltransferases (Schachter, 1995; Nishikawa et al., 1992; Minowa et al., 1998). Several novel sugar chains containing unique linkages have been described by Japanese investigators. For example, Glc-Ser was found in the blood coagulation factors (Hase et al., 1988). Furthermore, the recent finding of a galactose cap on the fucosyl residue linked to the trimannosyl core of the complextype N-linked sugar chains of octopus rhodopsin (Zhang et al., 1997) indicates that this fucosyl residue should no longer be considered as a termination signal as had long been believed. 100R Glycolipids Many glycolipids were found in animal tissues by Japanese researchers (Hakomori, 1981). Structural studies of various glycolipids found in fresh water animals by the group of Taro Hori (Hori et al., 1983; Hori and Sugita, 1993), and those in marine animals by Akira Hayashi’s group (Matsubara and Hayashi, 1986) established novel insights into the diversity of glycolipid structure. The number of glycolipids now known has increased by the development of sensitive analytical methods (Nagai and Iwamori, 1980). Finding of glycoceramidases (Ito and Yamagata, 1986) opened a new way to elucidate the structures of the sugar chains of glycosphingolipids, and to investigate their functional roles. Success of the stereo-controlled α-sialylation of several sugar residues by Kanie et al. (1988) opened a chemical way to synthesize gangliosides in large scale (Prabhanjan et al., 1991; Hasegawa and Kiso, 1994; Kiso and Hasegawa, 1994). This greatly contributed to the progress of the glycobiology in the field of glycolipids. A human promyelocytic leukemic cell line, HL-60, is known to have the dual potential to differentiate either to macrophages by exposure to phorbol esters or to granulocytes by exposure to dimethylsulfoxide. Masaki Saito and his collaborators (Saito, 1993) found that the amount of GM3 increases by differentiation to macrophages, whereas the amount of neolacto-series gangliosides increases by differentiation to granulocytes. Interestingly, the addition of GM3 and neolacto-series gangliosides to the culture of HL-60 cells induced them to differentiate into macrophages and granulocytes, respectively. These results suggested that the glycolipids may play direct roles in the differentiation of HL-60 cells. Much evidence suggested that gangliosides may modulate the mechanisms of growth hormone dependent transmembrane signalling. The finding by Higashi and Yamagata (1992) and Higashi et al. (1992) that GD1a and GD1b bind rather specifically to the calmodulin in mouse brain, and modulate calmodulin-dependent enzyme activation will open a promising field for future investigation. Sialic acids A very unique series of researches in the field of sialic acid has been reported by the group of Sadako Inoue and Yasuo Inoue. Inoue and Iwasaki (1978) found an α2–8 linked polyNeuGc in rainbow trout eggs. The importance of the polysialic acids in the organization of neural tissues was later recognized by many researchers after the finding of α2–8 linked polyNeuAc in neural cell adhesion molecule. By investigating the structures of polysialo-glycoproteins, purified from the cortical granule of eggs of various fishes, Inoue and colleagues found 3-deoxy-D-glycero-D-galacto-nonulosonic acid (KDN) (Nadano et al., 1986). KDN is an analogue of neuraminic acid, in which the amino group is replaced by the hydroxyl group. Further investigations revealed that KDN occurs linked to the sugar chains of glycoproteins and glycolipids in the same manner as sialic acids (Kanamori et al., 1990; Yu et al., 1991). Recently, Japanese researchers have reported the occurrence of KDN in mammalian tissues (Inoue et al., 1996). Therefore, KDN is one of the new members of the family of sialic acids, Glycobiology history in Japan and its expression in relation to the development of multicellular organisms is a very important target for current study. Proteoglycans Although proteoglycans should also be considered as glycoproteins, in that their sugar chains (glycosaminoglycans) are commonly linked to protein cores, the chains are much longer (100–200 monosaccharide residues) than the regular N- and O-linked sugar chains and contain many anionic residues, such as uronic acids and O- and N-sulfated sugars. It had long been believed that glycosaminoglycans have rather simple structures, based on disaccharide repeats. However, development of the reliable enzymatic methods to analyze the structures of the glycosaminoglycan chains by Sakaru Suzuki’s group (Oike et al., 1982) revealed the heterogeneity in these sugar chains. More recently, Imanari and co-workers have developed a postcolumn derivatization method for analyzing the disaccharide composition of glycosaminoglycans that can be applied to tissue samples and microorganisms (Toyoda et al., 1996). In addition, detailed structural studies of the linkage region have revealed the presence of sulfate and phosphate on galactose and xylose (Sugahara and Kitagawa, 2000). Elucidation of the detailed structures of glycosaminoglycans is also opening a new age for the study of proteoglycan function in Japan. Some cell growth factors require binding to heparan sulfate for the expression of their activities. Kimata and colleagues found that basic fibroblast growth factor binds specifically to a triple repeat of GlcNSO3-IdoA(2SO4) units (Habuchi et al., 1992), and hepatocyte growth factor binds to an octasaccharide region of heparan sulfate having at least two GlcNSO3(6SO4)-IdoA(2SO4) units (Ashikari et al., 1995). Purification and successful cloning of heparan sulfate 2-O (Kobayashi et al., 1997) and 6-O-sulfotransferases (Habuchi et al., 1998) led these investigators to propose that O-sulfations of heparan sulfate are the key reactions for their cell growth factor–related functions. Many examples indicating that the sulfation of sugar chains is important in various cellular recognition events in multi-cellular organisms were summarized recently in Trends in Glycoscience & Glycotechnology (Kawashima and Miyasaka, 2000; Takagaki and Ishido, 2000; Habuchi, 2000; Sugahara and Yamada, 2000). Important roles of aggrecan family proteoglycans in cell–cell and cell–substratum interactions during the brain development have also been reported by Oohira et al. (2000). In addition, use of p-nitrophenyl-xyloside as a reagent to inhibit specifically the chondroitin sulfate biosynthesis (Okayama et al., 1973) revealed many important roles of the glycosaminoglycans in the differentiation and developments of multicellular organisms. These compounds have been in widespread use; based on this work new derivatives have been made that can prime heparan sulfate (Fritz et al., 1994). The use of xylosides has also stimulated other investigators to examine other types of glycosides as primers (Sarkar et al., 1995, 1997). Turnover and degradation Most glycoconjugates are degraded in lysosomes. Their carbohydrate moieties are hydrolyzed by the concerted action of glycosidases that reside in lysosomes. Because most of these enzymes are exoglycosidases, the sugar chains are hydrolytically cleaved one by one from their nonreducing termini. In such a degradation mechanism, the entire set of exoglycosidases necessary to cleave all monosaccharide units in a sugar chain must be present for its complete degradation. If one of the enzymes is missing, the catabolism of the sugar chain stops at the point where the enzyme would have acted. Congenital deficiencies are known in almost all of exoglycosidases. In many of the deficiencies, glycolipids were shown to accumulate in lysosomes of cells, giving rise to the lysosomal storage diseases (Cervos-Navarro and Urich, 1995). Later on, the discovery of oligosaccharides in the urine of patients with lysosomal storage diseases (Wolfe et al., 1974), and their structural study (Nishigaki et al., 1978; Yamashita et al., 1979, 1980a, 1981a; Ohkura et al., 1981) revealed that the N-linked sugar chains of glycoproteins in the human body were released by the action of an endo-β-N-acetylglucosaminidase, which mainly occurs in the cytoplasm of cells (Tachibana et al., 1981). Based on the finding that large amounts of Asn-oligosaccharides are excreted in the urine of patients with fucosidosis (Yamashita et al., 1979), who lack lysosomal α-fucosidase, it was confirmed that the endo-β-N-acetylglucosaminidase does not work on the N-linked sugar chains with fucosylated trimannosyl core: Manα1–6(Manα1–3)Manβ1–4GlcNAcβ1–4(Fucα1–6)GlcNAc (Tachibana et al., 1982). Structural studies of the oligosaccharides and Asn-oligosaccharides in the urine of lysosomal storage diseases afforded much useful information regarding the structures of the N-linked sugar chains of human glycoproteins. Recently, Seko et al. (1991) reported the occurrence of peptide:N-glycanase, a similar enzyme as almond aminoglycopeptidase reported by Takahashi (1977), in animal tissues. Because no oligosaccharide with the GlcNAcβ1–4GlcNAc group at its reducing terminal was found in the urine samples of patients with lysosomal storage diseases, the enzyme may not work in the major catabolic pathway of glycoproteins, but rather plays an important role in posttranslational modification and/or remodification of glycoproteins. Functional studies of glycoproteins Turning to studies on the functional role of the N-linked sugar chains, we must not forget the important discovery and isolation of tunicamycin by Gakuzo Tamura and Akira Takatsuki (Takatsuki et al., 1971). The compound is the structural analogue of UDP-GlcNAc and contains a hydrophobic long chain fatty acid. Because of this, it works as the inhibitor of GlcNAc-1-phosphotransferase, that catalyzes the first step of the biosynthetic pathway of dolichol oligosaccharide precursors. Therefore, tunicamycin served as a specific inhibitor of the N-linked sugar chain biosynthesis and was used as an essential tool to elucidate many important roles of the sugar chains in the differentiation and development of multicellular organisms (Mizoguchi et al., 1981; Matsuda et al., 1982a,b). Increase in the structural information of the sugar chains of glycoconjugates has enabled researchers to consider their functional roles at the molecular level. Examples include: (1) The sugar chains of human chorionic gonadotropin that play an essential role in the hormonal action of this glycohormone (Kobata and Takeuchi, 1999). (2) Alteration of the sugar chain 101R A. Kobata structures of glycoproteins that occurs in various tumors (Nishimura and Kobata, 1996; Yamashita and Kobata, 1996a,b; Kobata, 1996). Successful use of these alterations for the diagnosis and prognosis of cancer has been reported in Japan (Nishimura and Kobata, 1996; Yamashita and Kobata, 1996a). The idea that some of these alterations may be the molecular basis of the unsocial behavior of malignant cells is now becoming one of the important working hypotheses to elucidate the mechanism of tumor metastasis. (3) Study of the sugar chains of immunoglobulin G has revealed that the galactose residues are playing an important role in the function of the Fc portion of this humoral defense molecule (Tsuchiya et al., 1989). Prominent deletion of galactose residue was found to occur in the sugar chains of serum immunoglobulin G obtained from patients with rheumatoid arthritis (Parekh et al., 1985). These findings have activated a new movement to elucidate the correlation of abnormalities of the sugar chains of glycoproteins with diseases, and are opening a new research area, which might be called glycopathology. Genetic approaches Development of gene technology in the past decade has been accelerating the functional study of the sugar chains of glycoproteins. With use of this technology, we can now obtain substantial amounts of bioactive proteins, which normally occur in very small amounts. However, producing glycoproteins in bacteria often does not result in the expected biological activities, because the sugar chains are not added. This, in turn, has stimulated interest by molecular biologists in the functional roles of the sugar chains. To obtain recombinant glycoproteins, cultured animal cell lines have been used instead of bacteria. However, through comparative study of the sugar chains of γ-glutamyltranspeptidases purified from kidneys and livers of various mammals (Kobata, 1992), occurrence of both organ and species differences were found in the sugar chains of glycoproteins. In addition, altered glycosylation occurs on recombinant glycoproteins when expressed in tumor cell lines. Many of the cell lines used have more or less malignant characters. Accordingly, structures of the sugar chains of recombinant glycoproteins could be affected by the cells used, despite having the same polypeptide backbone. Comparative studies of the N-linked sugar chains of natural human interferon-β1 (IFN-β1) and three recombinant IFN-β1s produced by different mammalian cell lines, transfected with the gene coding for human IFN-β1, revealed that their sugar patterns were different, although they all contain the same number of complex-type sugar chains (Kagawa et al., 1988). The differences occur both in the antennary structures and in the structures of outer chain moieties. This situation afforded a new way to elucidate the functions of the sugar chains of glycoproteins, by comparatively investigating the biological activities and the sugar chain structures of recombinant glycoproteins. A report by Takeuchi et al. (1989)) on the comparative study of recombinant human erythropoietin samples was the first example of such study. The examples listed above indicate that investigation of the sugar chains is essential for the sound development of gene technology and protein engineering. 102R Biotechnology and the future of glycosciences in Japan Much information obtained from glycobiology research is expected to be useful for the future development of biotechnology. In Japan, a report on “The Policy for Promoting General R&D for Basic Studies in Glycotechnology” was presented to the Minister of State for Science and Technology on July 26, 1990, by the Council for Aeronautics, Electronics and Other Advanced Technologies. Based on this report, national projects on glycotechnology sponsored by the Ministry of Science and Technology, the Ministry of International Trade and Industry (MITI), the Ministry of Health and Welfare (MHW), and the Ministry of Agriculture, Forestry and Fisheries were started in 1991. The MHW project was mainly directed to drug delivery systems, whereas the MITI project was directed at expanding our understanding of the functions of the sugar chains of glycoproteins and proteoglycans. A new genre in geneengineering opened with the production of mammalian cell lines with transgenically modified sets of glycosyltransferases (Fukuta et al., 2000), and the successful production of a Saccharomyces cerevisiae mutant that can synthesize mammalian N-glycans (Chiba et al., 1998). A new strategy for the synthesis of oligosaccharides and glycopeptides using the reverse reactions of exoglycosidases and endoglycosidases was developed by Ajisaka’s group (Matsuo et al., 1999; Ajisaka et al., 1998). Successful cloning of N-acetylglucosaminyltransferase IV (Minowa et al., 1998) and endo-β-N-acetylglucosaminidase M, together with the finding of a recognition motif for efficiently adding the O-linked sugar chains (Yoshida et al., 1997) has provided new tools for glycotechnology. A new analytical method for measuring binding of proteins to sugar chains using a biosensor (Shinohara et al., 1997) was also a major outcome of the MITI project. Many prominent accomplishments were made in the past decade supported by the grant money designated for glycobiology research based on the report described above. It had been estimated that at least 12 different sialyltransferases exist in mammals. Many of these enzymes were successfully cloned and their properties were determined by Tsuji (1996). Cloning of the glucuronyltransferase, which is responsible for the formation of HNK-1 epitope: the SO4-3GlcAβ1–3Galβ1–4GlcNAc group, and its transfection into COS-1 cells, revealed that the epitope works as an important signal to induce neural cell morphogenesis (Terayama et al., 1997). L-selectin, which is expressed on the surface of leukocytes, is considered to play an essential role for the homing of peripheral lymphocytes. However, the structure of its ligand remained unsolved for many years. Uchimura et al. (1998) contributed to this field by identifying sialyl-6-sulfo-Lex as the ligand of L-selectin. The work cited in this mini review represents only a part of the large number of glycobiology papers from Japan. Because of space limitations, only some of the relevant papers have been mentioned. Furthermore, glycobiology in Japan has both benefited from and contributed to advances in glycobiology around the globe. It is my hope that this mini review will help readers in tracing the research activities of glycobiology in Japan over the past half a century. Glycobiology history in Japan References Ajisaka, K., Fujimoto, H., and Miyasato, M. (1998) An α-L-fucosidase from Penicillium multicolor as a candidate enzyme for the synthesis of α-(1–3)-linked fucosyl oligosaccharides by transglycosylation. Carbohydr. Res., 309, 125–129. Amano, J., and Kobata, A. 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