Takashi Ohta

Chemical synthesis, folding, and structural insights into O-fucosylated epidermal growth factor-like repeat 12 of mouse Notch-1 receptor.

Notch receptors are cell surface glycoproteins that play key roles in a number of developmental cascades in metazoa. The extracellular domains of Notch-1 receptors are composed of 36 tandem epidermal growth factor (EGF)-like repeats, many of which are modified at highly conserved consensus sites by an unusual form of O-glycan, with O-fucose. The O-fucose residues on certain EGF repeats may be elongated. In mammalian cells this can be a tetrasaccharide, Siaα2,3Galβ1,4GlcNAcβ1,3Fucα1→. This elongation process is initiated by the action of O-fucose-specific β1,3 N-acetylglucosaminyltransferases of the Fringe family. There is evidence that the addition of GlcNAc by Fringe serves as an essential modulator of the interaction of Notch with its ligands and the triggering of activation. Here we describe the efficient synthesis, folding, and structural characterization of EGF repeat 12 (EGF 12) of a mouse Notch-1 receptor bearing different O-fucose glycan chains. We demonstrate that the three disulfide bonds, Cys(456)-Cys(467) (C1-C3), Cys(461)-Cys(476) (C2-C4), and Cys(478)-Cys(487) (C5-C6) were correctly formed in the nonglycosylated as well as the O-fucosylated forms of EGF 12. Three-dimensional structural studies by NMR reveal that the methyl group of fucose is in close contact with ILe(475), Met(477), Pro(478) residues and this stabilizes the conformation of the antiparallel β-sheet of EGF 12. The addition of the GlcNAc residue on O-fucosylated EGF 12 induces a significant conformational change in the adjacent tripeptide sequence, Gln(462)Asn(463)Asp(464), which is a motif involved in the natural, enzymatic O-fucosylation at the conserved site (Cys(461)X(4)Ser/ThrCys(467)).

Artificial Golgi Apparatus: Globular Protein-like Dendrimer Facilitates Fully Automated Enzymatic Glycan Synthesis

Despite the growing importance of synthetic glycans as tools for biological studies and drug discovery, a lack of common methods for the routine synthesis remains a major obstacle. We have developed a new method for automated glycan synthesis that employs the enzymatic approach and a dendrimer as an ideal support within the chemical process. Recovery tests using a hollow fiber ultrafiltration module have revealed that monodisperse G6 (MW = 58 kDa) and G7 (MW = 116 kDa) poly(amidoamine) dendrimers exhibit a similar profile to BSA (MW = 66 kDa). Characteristics of the globular protein-like G7 dendrimer with high solubility and low viscosity in water greatly enhanced throughput and efficiency in automated synthesis while random polyacrylamide-based supports entail significant loss during the repetitive reaction/separation step. The present protocol allowed for the fully automated enzymatic synthesis of sialyl Lewis X tetrasaccharide derivatives over a period of 4 days in 16% overall yield from a simple N-acetyl-d-glucosamine linked to an aminooxy-functionalized G7 dendrimer.

An efficient synthesis of a biantennary sialooligosaccharide analog using a 1,6-anhydro-β-lactose derivative as a key synthetic block

Abstract An efficient and versatile method for the synthesis of a biantennary octasaccharide derivative was established by combined chemical and enzymatic manipulations of 1,6-anhydro-β-lactose as a key starting material. A key 1,6-anhydro-β-lactose derivative having two unprotected hydroxyl groups at C-3′ and C-6′ positions was prepared and employed for the chemical coupling reaction with a known 3,4,6-tri- O -acetyl-2-deoxy-2-phthalimido-β- d -glucopyranosyl imidate to afford a tetrasaccharide derivative with two GlcNAc branches in 69% yield. Enzymatic galactosylation using UDP-Gal with a bovine milk β1,4-galactosyltransferase and subsequent sialylation with a recombinant α2,3-sialyltransferase in the presence of CMP-Neu5Ac proceeded smoothly and gave a desired model compound, a bivalent sialooctasaccharide ( 1 ), in 73% overall yield from the tetrasaccharide intermediate.