Most secretory and transmembrane proteins are posttranslationally modified with various glycans. The structures of glycans attached to the proteins depend on proteins, cells, tissues, ages, species and individuals. However, the mechanism of regulation to generate such diverse glycans in a cell has not been revealed. In this review, we would like to discuss our finding, “Golgi units” that would regulate the variety of glycosylation.
The mechanochemical studies of carbohydrate ring flipping by both top-down and bottom-up approaches are surveyed. In the top-down approaches, the traction studies of polysaccharides by atomic force microscopy (AFM) disclosed their interesting behavior: they become abruptly flexible at certain pulling forces due to the synchronous ring flips of the monosaccharide units. This abrupt flexibility confers a shockabsorbing mechanism on glycoproteins and glyco-coated cells. Regarding the bottom-up approach, we succeeded in controlling the ring flip of carbohydrates to find that a 2, 4-diaminoxylose derivative (hinge sugar) easily undergoes the ring flip by chelation to a metal ion at the amino groups. The metal-ion-induced bending of the hinge sugar was even more efficient when it was incorporated in a trisaccharide, probably due to the interaction between the reducing and non-reducing terminus sugars. For application, we invented a hinge-sugar-based metal ion sensor, in which a chelationdriven and pliers-like motion of the dipyrenylmethyl hinge sugar causes stacking of two pyrene groups, giving rise to excimer fluorescence. Hinge sugar was also applicable to the tether in a [2+2] cycloaddition reaction. These studies emphasize a new aspect of carbohydrates as motional components in biology and material science.
This article describes the design, synthesis and properties of novel β-glycosidase inhibitors, β-glycosylamidines, aiming at developing easily accessible glycosidase inhibitors that could be used as an affinity ligand. β-Glycosylamidines, in which glycopyranose is connected via a β-N-glycoside linkage with a substituted amidine, are easily accessible, but highly potent β-glycosidase inhibitors. The inhibition is selective with respect to the enzyme's glyconand stereospecificities, and a series of β-glycosylamidines of different glycon types is synthesized in quantities from the corresponding sugar in two steps. The positively charged amidine bound tightly with the enzyme active site by charge interaction with an anionic form of the catalytic acid/base carboxy group. The properties of β-glycosylamidines have been used successfully as an affinity ligand for the purification of β-glycosidases from natural samples according to the glycon substrate specificity. Despite high affinity with the ligand, the adsorbed enzyme was eluted readily by adding sugar or by lowering the pH below the pKa of the catalytic acid/base carboxy of the enzyme. The latter method is applicable to the affinity purification of a wide variety of β-glycosidases by controlling the adsorption and desorption properties by changing the pH.
We have been interested in the relationships between the structure and biological function of glycosphingolipids from invertebrate species. This review describes the oligosaccharide syntheses and biological activities of glycosphingolipids in invertebrates, focusing especially on the glycosphingolipids found in cestoda parasite, millipede, nematoda parasite and marine sponge.