Inhibitors of glycoprotein biosynthesis

Inhibition of L-fucokinase from rat liver by L-fucose analogues in vitro

By investigating the effects of more than 15 different L-fucose analogues on the activity of L-fucokinase (EC 2.7.1.52) from rat liver in vitro, certain structural requirements for potent inhibition of this enzyme were established. Of the novel compounds, 4,6-dideoxy-L-xylo-hexopyranose (4) and methyl 4,6-dideoxy-4-iodo-L-glucopyranose (9) were found to be competitive inhibitors with Ki-values of 0.5 mM and 5.0 mM respectively. Thus 4,6-dideoxy-L-xylo-hexopyranose is a better inhibitor of L-fucokinase than methyl-alpha-L-fucoside (1). Uptake of L-fucose into rat hepatoma cells is reduced by 52% in the presence of the deoxy derivative (4), leading to a decrease of 45% in the incorporation of L-fucose into total cellular glycoproteins.

Inhibition of N-acetylglucosamine kinase and N-acetylmannosamine kinase by 3-O-methyl-N-acetyl-D-glucosamine in vitro

During the search for inhibitors of N-acetylneuraminic acid biosynthesis, it was shown that 3-O-methyl-N-acetylglucosamine competitively inhibits the N-acetylglucosamine kinase of rat liver in vitro with a Ki value of 17 microM. N-Acetylmannosamine kinase is inhibited non-competitively with a Ki value of 80 microM. In a human hepatoma cell line (HepG2), 3-O-methyl-N-acetyl-D-glucosamine (1 mM) inhibits the incorporation of 14C-N-acetylglucosamine and 14C-N-acetylmannosamine into cellular glycoproteins by 88% and 70%, respectively.

Inhibition of the biosynthesis of N-acetylneuraminic acid by metal ions and selenium in vitro

In liver homogenate the biosynthesis of N-acetylneuraminic acid using N-acetylglucosamine as precursor can be followed stepwise by applying different chromatographic procedures. In this cell-free system 16 metal ions (Zn2+, Mn2+, La3+, Co2+, Cu2+, Hg2+, VO3-, Pb2+, Ce3+, Cd2+, Fe2+, Fe3+, Al3+, Sn2+, Cs+ and Li+) and the selenium compounds, selenium(IV) oxide and sodium selenite, have been checked with respect to their ability to influence a single or possibly several steps of the biosynthesis of N-acetylneuraminic acid. It could be shown that the following enzymes are sensitive to these metal ions (usually applied at a concentration of 1 mmol l-1): N-acetylglucosamine kinase (inhibited by Zn2+ and vandate), UDP-N-acetylglucosamine-2'-epimerase (inhibited by Zn2+, Co2+, Cu2+, Hg2+, VO3-, Pb2+, Cd2+, Fe3+, Cs+, Li+, selenium(IV) oxide and selenite), and N-acetylmannosamine kinase (inhibited by Zn2+, Cu2+, Cd2+ and Co2+). Dose dependent measurements have shown that Zn2+, Cu2+ and selenite are more efficient inhibitors of UDP-N-acetylglucosamine-2'-epimerase than vanadate. As for the N-acetylmannosamine kinase inhibition, a decreasing inhibitory effect exists in the following order Zn2+, Cd2+, Co2+ and Cu2+. In contrast, La3+, Al3+ and Mn2+ (1 mmol l-1) did not interfere with the biosynthesis of N-acetylneuraminic acid. Thus, the conclusion that the inhibitory effect of the metal ions investigated cannot be regarded as simply unspecific is justified.

Inhibition of terminal N- and O-glycosylation specific for herpesvirus-infected cells: mechanism of an inhibitor of sugar nucleotide transport across Golgi membranes

The nucleoside analog (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVdU) inhibited the Golgi-associated terminal glycosylation in herpes simplex virus type 1- and type 2-infected cells, specifically incorporation of galactose and sialic acid into N-linked oligosaccharides, and incorporation of sialic acid and, to a lesser extent, of galactose into O-linked oligo saccharides. This resulted in formation of viral glycoproteins with terminal GlcNAc and Fuc in N-linked oligosaccharides and terminal O-linked GalNAc. Inhibition of formation of UDP-hexoses and of acceptor glycoprotein synthesis and inhibition of cellular transport of viral glycoproteins were not observed. No evidence for the formation of a sugar nucleotide analog of BVdU was obtained. Inhibition required phosphorylation of BVdU to its 5' monophosphate (BVdUMP) by the virus-coded thymidine kinase. In a cell-free system, this monophosphate inhibited the transport of pyrimidine sugar nucleotides across Golgi membranes and, as a consequence, the incorporation of sugars into glycoproteins. Inhibition of galactosyltransferase by BVdUMP was insignificant. BVdUMP did not inhibit translocation across the Golgi membrane of purine sugar nucleotides. Inhibition of sugar nucleotide translocation represents the first target for design of virus-specific glycosylation inhibitors.