Sugar analogs can be used as a probe for glycans or as inhibitors of glycosylation. Here, the actions of both existing and our own recently developed fucose analogs are described. Glycans containing fucose are involved in the pathology of diseases, including inflammation, COPD (chronic obstructive pulmonary disease) and cancer as well as basic biological phenomena, including development, immunity, and neural functions. Therefore, developing detection probes and inhibitors of fucosylation is desirable. Although several fucose analogs for detection and inhibition have been developed, these analogs have problems with sensitivity, toxicity, and potency. We have recently developed a highly sensitive probe for fucosylated glycans with low toxicity, “7-alkynyl-fucose.” This probe is a better substrate for various fucosyltransferases compared with an existing probe, leading to efficient incorporation into glycans and highly sensitive detection of glycans. In addition, we found that another fucose analog, “6-alkynyl-fucose,” is a potent inhibitor of fucosylation and has the potential to suppress cancer invasion. The mechanism of action was revealed to be selective inhibition of the GDP-fucose biosynthetic enzyme FX. These results show that fucose analogs are potentially powerful research tools, and a glyco-chemical biology approach toward the detection and inhibition of glycans using sugar analogs is expected to be developed in future.

Sialidase catalyzes the removal of sialic acids from glycoconjugates. While the physiological functions of mammalian sialidases have been elucidated, sialidases in other vertebrates, including those in fish, are not well understood. Recently, increased genomic resources in fish have become available, which will facilitate research on fish sialidase.

Here, three fish orders (Cypriniformes, Beloniformes and Perciformes) have been selected to compare the properties of their sialidases. A Neu1 knockdown in medaka by a morpholino oligo resulted in the accumulation of Sia α2-3 linked sialoglycoproteins, leading to malfunctions in heart beating, embryo growth, hatching, and swimming, indicating that lysosomal Neu1 is a crucial factor for embryogenesis.

Fish Neu3 and Neu4 function varies between fish species. Medaka and tilapia Neu3a localize at the plasma membrane, as is seen in humans. Zebrafish Neu3.1 is an ER sialidase, with an optimal pH (pH 2.6). Neu4 shows high diversity in subcellular localization: medaka and zebrafish Neu4 are detected at the lysosome and ER, respectively. Surprisingly, tilapia Neu4 is detected at nucleus, which makes it the first nuclear sialidase to be identified. Moreover, importin has been identified as a regulator of tilapia Neu4 functions. These results demonstrate the diversity of sialidase functions among fish species and the requirement of further fish research.

Glycosidases play vital roles in the degradation of oligo- and polysaccharides. To date, many glycosidases have been isolated from microorganisms, plants, and animals, and have been used in industrial applications. Although microorganisms are important resources of novel and useful glycosidases, we are currently unable to culture most microorganisms in the laboratory. The metagenomic approach, which is a culture-independent method used to obtain genomic information regarding environmental microorganisms, is a powerful tool for the isolation of genes encoding novel glycosidases from microorganisms. This review introduces unique characters and biotechnological applications of β-glucosidases and a β-xylosidase/α-L-arabinofuranosidase isolated with the metagenomic approach.

Autophagy is a conserved degradation pathway driven by the sequestration of various cytoplasmic components into the vacuoles/lysosomes in eukaryotic cells. Autophagy is known to play an important role in cellular homeostasis by eliminating excess/damaged organelles or by providing amino acids during nutrition starvation. Several studies have suggested that dysregulation of autophagy causes physiological dysfunction in both yeast and mammals. It has been reported that the magnitude of autophagy is strongly enhanced by starvation of various nutrition sources, such as nitrogen, carbon and phosphorus. However, the regulatory mechanism and physiology of autophagy induced by each nutritional shortage—with the exception of nitrogen starvation—have been largely unclear. In this review, I focus on recent studies of the regulation and physiology of autophagy induced by glucose (or carbon source) starvation, as well as the historical background of autophagy study in Saccharomyces cerevisiae. Our recent findings indicate that autophagy plays a role in facilitating degradation of the intracellular mannosyl glycan during glucose starvation in budding yeast.

Recently, it has been elucidated that the lattice structure formed by complexes of galectins and N-glycans regulates expression and function of plasmalemmal glycoproteins, which is important for maintaining various homeostatic systems. We have previously revealed that the failure of N-glycosylation abolishes lattice formation and induces aberrant membrane sub-domain distribution of Glucose transporter 2 (GLUT2) in pancreatic β cells that consequently attenuates the cellular glucose uptake function. This results in the impairment of insulin secretion in pancreatic β cells in the disease process of diabetes. Although the biological significance of the formation of the galectin lattice is well recognized, the molecular regulatory mechanism of the localization and function of plasmalemmal glycoproteins has not been clarified. To address the question, we analyzed the component proteins of the galectin lattice complexes on pancreatic β cell surface and found that the lattice complexes were composed of Cationic amino acid transporter 3 (CAT3), Teneurin-3, Myosin-4, Actin, α-Tubulin, and GLUT2 at least. These results indicated that the galectin lattice forms clusters of plasmalemmal glycoproteins through galectin-N-glycan bindings and further suggested the presence of the common mechanism among the functional regulation of nutrition sensors in the insulin secretion of pancreatic β cells.

Sugar analogs can be used as a probe for glycans or as inhibitors of glycosylation. Here, the actions of both existing and our own recently developed fucose analogs are described. Glycans containing fucose are involved in the pathology of diseases, including inflammation, COPD (chronic obstructive pulmonary disease) and cancer as well as basic biological phenomena, including development, immunity, and neural functions. Therefore, developing detection probes and inhibitors of fucosylation is desirable. Although several fucose analogs for detection and inhibition have been developed, these analogs have problems with sensitivity, toxicity, and potency. We have recently developed a highly sensitive probe for fucosylated glycans with low toxicity, “7-alkynyl-fucose.” This probe is a better substrate for various fucosyltransferases compared with an existing probe, leading to efficient incorporation into glycans and highly sensitive detection of glycans. In addition, we found that another fucose analog, “6-alkynyl-fucose,” is a potent inhibitor of fucosylation and has the potential to suppress cancer invasion. The mechanism of action was revealed to be selective inhibition of the GDP-fucose biosynthetic enzyme FX. These results show that fucose analogs are potentially powerful research tools, and a glyco-chemical biology approach toward the detection and inhibition of glycans using sugar analogs is expected to be developed in future.

Sialidase catalyzes the removal of sialic acids from glycoconjugates. While the physiological functions of mammalian sialidases have been elucidated, sialidases in other vertebrates, including those in fish, are not well understood. Recently, increased genomic resources in fish have become available, which will facilitate research on fish sialidase.

Here, three fish orders (Cypriniformes, Beloniformes and Perciformes) have been selected to compare the properties of their sialidases. A Neu1 knockdown in medaka by a morpholino oligo resulted in the accumulation of Sia α2-3 linked sialoglycoproteins, leading to malfunctions in heart beating, embryo growth, hatching, and swimming, indicating that lysosomal Neu1 is a crucial factor for embryogenesis.

Fish Neu3 and Neu4 function varies between fish species. Medaka and tilapia Neu3a localize at the plasma membrane, as is seen in humans. Zebrafish Neu3.1 is an ER sialidase, with an optimal pH (pH 2.6). Neu4 shows high diversity in subcellular localization: medaka and zebrafish Neu4 are detected at the lysosome and ER, respectively. Surprisingly, tilapia Neu4 is detected at nucleus, which makes it the first nuclear sialidase to be identified. Moreover, importin has been identified as a regulator of tilapia Neu4 functions. These results demonstrate the diversity of sialidase functions among fish species and the requirement of further fish research.

Glycosidases play vital roles in the degradation of oligo- and polysaccharides. To date, many glycosidases have been isolated from microorganisms, plants, and animals, and have been used in industrial applications. Although microorganisms are important resources of novel and useful glycosidases, we are currently unable to culture most microorganisms in the laboratory. The metagenomic approach, which is a culture-independent method used to obtain genomic information regarding environmental microorganisms, is a powerful tool for the isolation of genes encoding novel glycosidases from microorganisms. This review introduces unique characters and biotechnological applications of β-glucosidases and a β-xylosidase/α-L-arabinofuranosidase isolated with the metagenomic approach.

Autophagy is a conserved degradation pathway driven by the sequestration of various cytoplasmic components into the vacuoles/lysosomes in eukaryotic cells. Autophagy is known to play an important role in cellular homeostasis by eliminating excess/damaged organelles or by providing amino acids during nutrition starvation. Several studies have suggested that dysregulation of autophagy causes physiological dysfunction in both yeast and mammals. It has been reported that the magnitude of autophagy is strongly enhanced by starvation of various nutrition sources, such as nitrogen, carbon and phosphorus. However, the regulatory mechanism and physiology of autophagy induced by each nutritional shortage—with the exception of nitrogen starvation—have been largely unclear. In this review, I focus on recent studies of the regulation and physiology of autophagy induced by glucose (or carbon source) starvation, as well as the historical background of autophagy study in Saccharomyces cerevisiae. Our recent findings indicate that autophagy plays a role in facilitating degradation of the intracellular mannosyl glycan during glucose starvation in budding yeast.

Recently, it has been elucidated that the lattice structure formed by complexes of galectins and N-glycans regulates expression and function of plasmalemmal glycoproteins, which is important for maintaining various homeostatic systems. We have previously revealed that the failure of N-glycosylation abolishes lattice formation and induces aberrant membrane sub-domain distribution of Glucose transporter 2 (GLUT2) in pancreatic β cells that consequently attenuates the cellular glucose uptake function. This results in the impairment of insulin secretion in pancreatic β cells in the disease process of diabetes. Although the biological significance of the formation of the galectin lattice is well recognized, the molecular regulatory mechanism of the localization and function of plasmalemmal glycoproteins has not been clarified. To address the question, we analyzed the component proteins of the galectin lattice complexes on pancreatic β cell surface and found that the lattice complexes were composed of Cationic amino acid transporter 3 (CAT3), Teneurin-3, Myosin-4, Actin, α-Tubulin, and GLUT2 at least. These results indicated that the galectin lattice forms clusters of plasmalemmal glycoproteins through galectin-N-glycan bindings and further suggested the presence of the common mechanism among the functional regulation of nutrition sensors in the insulin secretion of pancreatic β cells.