Glycosyl phosphate repeating units are found in the capsular polysaccharides of Neisseria meningitidis and Streptococcus pneumoniae. Capsular polysaccharides help these pathogens avoid the immune system responses of hosts by masking the highly antigenic constituent of the pathogens. In addition, capsular polysaccharides are recognized as antigens by the immune system of hosts. The lipophosphoglycans (LPGs) of Leishmania contain characteristic disaccharide 1-phosphate repeating units. It has been reported that LPGs play important roles in the survival and infection of Leishmania, and LPGs are recognized as antigens. Thus, the chemical synthesis of these biomolecules and their chemical analogs can help to elucidate their biological functions and facilitate the development of vaccines and pharmaceuticals. This paper describes the methods developed by our group for the synthesis of glycosyl phosphates using phosphonic acid derivatives. ...and more
Previously, we reported a series of methodologies to prepare and analyze N-glycans, O-glycans, glycosaminoglycans, glycosphingolipid-glycans, and free oligosaccharides by mass spectrometry (MS) and high-performance liquid chromatography. Each procedure to analyze different classes of glycoconjugate glycans was combined and the entire sub-glycan components could be visualized in the cellular or serum glycome, the so-called total glycome. Recently, we have developed and improved the technologies for glycomic analyses and established sialic acid linkage-specific alkylamidation (SALSA) to distinguish sialylated glycan isomers by MS analysis.
In segment 2 of the Human Glycome Atlas Project (HGA), the generation of a large-scale human glycome catalog (total human plasma glycome) is one of the most important missions to construct a database called TOHSA. In this section, we introduce our latest studies, covering 2) the improved analysis of N-glycans by a glycoblotting method in combination with sialic linkage-specific derivatization to distinguish sialylated glycan isomers, and 3) the development of an automated N-glycan preparation instrument for large-scale glycomic analysis of human plasma/serum. ...and more
Galectins are saccharide-binding proteins with characteristic amino acid sequences in the carbohydrate recognition domain. Many members of the galectin family also show two other features: they reside both inside as well as outside of cells and they bind multiple partners through protein-protein interactions. Inside cells, some examples of non-carbohydrate ligands of various galectins include: (a) prototype galectin-1 binds to oncogene H-Ras and transcription factors OCA-B and TFII-I; (b) tandem-repeat type galectin-8 binds to other galectins such as galectin-9, the autophagy receptor NDP52, and tripartite motif protein TRIM5α; and (c) the NH2-terminal domain of chimera type galectin-3 binds to components of the endosomal sorting complex required for transport such as Tsg101 and to ribonucleoprotein complexes such as hnRNP A2B1 while the COOH-terminal domain binds to the apoptosis repressor Bcl-2, tripartite motif protein TRIM16, and transcription factors OCA-B, TFII-I, and β-catenin. The present article aims to summarize selected studies that highlight the promiscuity of intracellular galectins and several intriguing questions raised by these findings. ...and more
The chemical synthesis of glycosidic bonds (glycosylation) is a key reaction enabling the artificial synthesis of various glycoconjugates and polysaccharides. Glycosylation involves a nucleophilic substitution process between a glycosyl donor, in which various leaving groups are introduced at the anomeric carbon of a sugar, and an acceptor molecule. Nucleophilic substitution reactions are elementary organic chemistry reactions encountered at an introductory university level, and it might seem that established methods for controlling them exist. However, this reaction progresses through a complex process, distinct from typical nucleophilic substitutions, wherein the electrophilic donor forms an equilibrium mixture composed of various constituents. Due to this complexity, the control of glycosylation reactions often relies on the trial and error based on the synthetic chemist’s experience and intuition. To overcome this situation, elucidation of the molecular mechanisms involved in this reaction has been pursued by many researchers. This paper focuses on evaluating the chemical properties of ion pairs, which are crucial in the elucidation of the reaction mechanisms of glycosylation, and introduces various studies in this field. ...and more
