We found a new enzyme that efficiently catalyzes transglycosylation reaction toward phenolic hydroxyl groups. The enzyme, hydroquinone glucosylating enzyme, catalyzed α-anomer selective glycosylation of hydroquinone, and the yield of the resulting product, 4-hydroxyphenyl-O-α-D-glucopyranoside, was high enough to be used for industrial production. Kojic acid, caffeic acid, and many other phenolic compounds were also glycosylated by the reaction of this enzyme. However, alcohols were not glycosylated by the enzyme. The application studies of 4-hydroxyphenyl-O-α-D-glucopyranoside, i.e., α-arbutin were carried out. α-Arbutin strongly inhibited human tyrosinase, and its inhibitory effect on human tyrosinase was much higher than that of its isomer, 4-hydroxyphenyl-O-β-D-glucopyranoside, i.e., arbutin. We also synthesized some kinds of glycosides of α-arbutin and arbutin. The comparison of their inhibitory effects on human tyrosinase indicated that the molecular size and electrostatic potentials around the benzene ring are important for inducing the inhibitory effect of hydroquinone glycosides toward human tyrosinase. We examined the inhibitory effects of α-arbutin on melanin biosynthesis. α-Arbutin inhibited melanin syntheses of HMV-II cells and human skin model in a dose-dependent manner at noncytotoxic concentrations. These results demonstrate that α-arbutin is an effective and safe ingredient for skin-lightening.
Comprehensive analyses of proteins from cells and tissues are the most effective means of elucidating the expression patterns of individual disease-related proteins. On the other hand, the simultaneous separation and characterization of proteins by electrophoresis followed by MS analysis is one of the fundamental approaches to proteomic analysis. However, these analyses do not permit the complete structural identification of glycans in glycoproteins or their structural characterization. Over half of all known proteins are glycosylated and glycan analyses of glycoproteins are requisite for fundamental proteomics studies. The analysis of glycan structural alterations in glycoproteins is becoming increasingly important in terms of biomarkers, quality control of glycoprotein drugs, and the development of new drugs. However, the usual glycomics approach which characterizes and/or identifies glycans, provides some structural information, but it does not provide any information on the functionality of glycans. Therefore, in order to elucidate the function of glycans, functional glycomics which identifies the target glycoproteins of glycosyltransferases and characterizes functional roles of glycans represents a promising approach. In this review, we show examples of a functional glycomics technique using α1,6 fucosyltransferase gene (Fut8) in order to identify the target glycoproteins.
Lymphocyte homing to secondary lymphoid organs has been extensively studied during the past quarter century. The first stage of lymphocyte homing is known as “lymphocyte rolling,” which occurs in high endothelial venules (HEV) of lymph nodes. Lymphocyte rolling in HEV of peripheral lymph nodes is dependent on L-selectin expressed on lymphocytes. The L-selectin ligand is comprised of sialylated sulfated oligosaccharide, 6-sulfo sialyl Lewis X (sLeX). For many years, the MECA-79 monoclonal antibody, the epitope of which was subsequently shown to be an O-linked oligosacchride, has been used to stain HEV and the relationship between the MECA-79 antigen and L-selectin ligands has been discussed. Recently, targeted disruption of glycosyltransferases and related enzymes revealed the critical structure of L-selectin ligands and the significance of the MECA-79 antigen. This paper describes the structural basis of L-selectin ligand oligosaccharides and MECA-79 antigen.
UDP-GalNAc: polypeptide N-acetylgalactosaminyl transferase (GalNAc-transferase, GalNAc-T) is the enzyme catalyzing mucin-type O-glycosylation (GalNAcα1-O-Ser/Thr) of proteins. Mutations in the gene encoding the GalNAc-T3 isoform were recently identified as a cause of the autosomal recessive metabolic disorder familial tumoral calcinosis (FTC) (OMIM 211900). FTC is associated with hyperphosphatemia and massive ectopic calcifications. We recently demonstrated that the secretion of the phosphaturic factor FGF23 requires O-glycosylation, and that GalNAc-T3 selectively directs O-glycosylation in a subtilisin-like proprotein convertase recognition sequence motif, which blocks furin protease processing of FGF23. These results suggest a novel posttranslational regulatory model of FGF23 involving competing O-glycosylation and protease processing to produce intact FGF23.