Synthetic potential of cloned fucosyl-transferase III and VI

Enzymatic glycosylation involving fluorinated carbohydrates

Fluorinated carbohydrates, where one (or more) fluorine atom(s) have been introduced into a carbohydrate structure, typically through deoxyfluorination chemistry, have a wide range of applications in the glycosciences. Fluorinated derivatives of galactose, glucose, N-acetylgalactosamine, N-acetylglucosamine, talose, fucose and sialic acid have been employed as either donor or acceptor substrates in glycosylation reactions. Fluorinated donors can be synthesised by synthetic methods or produced enzymatically from chemically fluorinated sugars. The latter process is mediated by enzymes such as kinases, phosphorylases and nucleotidyltransferases. Fluorinated donors produced by either method can subsequently be used in glycosylation reactions mediated by glycosyltransferases, or phosphorylases yielding fluorinated oligosaccharide or glycoconjugate products. Fluorinated acceptor substrates are typically synthesised chemically. Glycosyltransferases are most commonly used in conjunction with natural donors to further elaborate fluorinated acceptor substrates. Glycoside hydrolases are used with either fluorinated donors or acceptors. The activity of enzymes towards fluorinated sugars is often lower than towards the natural sugar substrates irrespective of donor or acceptor. This may be in part attributed to elimination of the contribution of the hydroxyl group to the binding of the substrate to enzymes. However, in many cases, enzymes still maintain a significant activity, and reactions may be optimised where necessary, enabling enzymes to be used more successfully in the production of fluorinated carbohydrates. This review describes the current state of the art regarding chemoenzymatic production of fluorinated carbohydrates, focusing specifically on examples of the enzymatic production of activated fluorinated donors and enzymatic glycosylation involving fluorinated sugars as either glycosyl donors or acceptors.

A one-pot enzymatic approach to the O-fluoroglucoside of N-methylanthranilate

In connection with prospective (18)F-PET imaging studies, the potential for enzymatic synthesis of fluorine-labelled glycosides of small molecules was investigated. Approaches to the enzymatic synthesis of anomeric phosphates of d-gluco-configured fluorosugars proved ineffective. In contrast, starting in the d-galacto series and relying on the consecutive action of Escherichia coli galactokinase (GalK), galactose-1-phosphate uridylyltransferase (GalPUT), uridine-5'-diphosphogalactose 4-epimerase (GalE) and oat root glucosyltransferase (SAD10), a quick and effective synthesis of 6-deoxy-6-fluoro-d-glucosyl N-methylanthranilate ester was achieved.

Biochemical characterization of Helicobacter pylori α-1,4 fucosyltransferase: metal ion requirement, donor substrate specificity and organic solvent stability

The effect of metal ions on the activity, the donor substrate specificity, and the stability in organic solvents of Helicobacter pylori α-1,4 fucosyltransferase were studied. The recombinant enzyme was expressed as soluble form in E. coli strain AD494 and purified in a one step affinity chromatography. Its activity was highest in cacodylate buffer at pH 6.5 in the presence of 20 mM Mn2+ ions at 37°C. Mn2+ ions could be substituted by other metal ions. In all cases, Mn2+ ions proofed to be the most effective (Mn2+ > Co2+ > Ca2+ > Mg2+ > Cu2+ > Ni2+ > EDTA). The enzyme shows substrate specificity for Type I disaccharide (1) with a KM of 114 μM. In addition, the H. pylori α-1,4 fucosyltransferase efficiently transfers GDP-activated L-fucose derivatives to Galβ1-3GlcNAc-OR (1). Interestingly, the presence of organic solvents such as DMSO and methanol up to 20% in the reaction medium does not affect significantly the enzyme activity. However, at the same concentration of dioxane, activity is totally abolished.

Synthesis of bisubstrate analogues targeting α-1,3-fucosyltransferase and their activities

We designed two bisubstrate analogues targeting alpha-1,3-fucosyltransferases, based on the three dimensional structure of Lewis X, which is the product of a alpha-1,3-fucosyltransferase reaction. We selected guanosine-5'-diphospho-L-galactose as a donor mimic and 2-hydroxyethyl beta-D-galactoside as an acceptor mimic, and tethered these two mimics with a methylene or ethylene linker. For the synthesis, the 6-position of L-galactose and the 6-position of D-galactose were first tethered via a methylene or ethylene linker. The L-galactose moiety was then converted to a GDP derivative. Both bisubstrate analogues were moderate inhibitors against alpha-1,3-fucosyltransferase V and VI. The fact that they were substrates of alpha-1,3-fucosyltransferase VI suggested that these compounds bound to the donor binding site, but not to the acceptor binding site.

Chemo-enzymatic synthesis of fluorinated sugar nucleotide: useful mechanistic probes for glycosyltransferases

An effective procedure for the synthesis of 2-deoxy-2-fluoro-sugar nucleotides via Select fluor-mediated electrophilic fluorination of glycals with concurrent nucleophilic addition or chemo-enzymatic transformation has been developed, and the fluorinated sugar nucleotides have been used as probes for glycosyltransferases, including fucosyltransferase III, V, VI, and VII, and sialyl transferases. In general, these fluorinated sugar nucleotides act as competitive inhibitors versus sugar nucleotide substrates and form a tight complex with the glycosyltransferase.

Substrate specificity of fucosyl transferase III: An efficient synthesis of sialyl Lewisx-, sialyl Lewisa-derivatives and mimetics thereof

Fucosyl transferase III (FucT III) has previously been characterized as the most general enzyme of the FucT family, as judged from its ability to catalyze the transfer of fucose to both Galβ(1-3)GlcNAc and Galβ(1-4)GlcNAc. In order to explore the synthetic potential of FucT III for the enzymatic synthesis of sialyl Lewisx and sialyl Lewisa derivatives, its substrate specificity has been probed using a number of natural substrate mimetics. A remarkable range of acceptor substrates was found when N-acetyl glucosamine was replaced by D-glucal, (R,R)-1,2-cyclohexanediol and (R,R)-butan-2,3-diol. Although the reaction rates were low compared to the reaction with the natural substrates, they proved to be sufficient for the synthesis of preparative amounts.Key words: fucosyl transferase III, sialyl Lewisa, sialyl Lewisx, carbohydrate mimetics.

Fucose in N-glycans: from plant to man

Fucosylated oligosaccharides occur throughout nature and many of them play a variety of roles in biology, especially in a number of recognition processes. As reviewed here, much of the recent emphasis in the study of the oligosaccharides in mammals has been on their potential medical importance, particularly in inflammation and cancer. Indeed, changes in fucosylation patterns due to different levels of expression of various fucosyltransferases can be used for diagnoses of some diseases and monitoring the success of therapies. In contrast, there are generally at present only limited data on fucosylation in non-mammalian organisms. Here, the state of current knowledge on the fucosylation abilities of plants, insects, snails, lower eukaryotes and prokaryotes will be summarised.

Glycosyltransferase catalyzed assemblage of sialyl-Lewis(a)-saccharopeptides

A series of methyl hexopyranosiduronic acids are coupled to type I disaccharide amines to give 'trisaccharides' which have the natural N-acetyl group of the type I disaccharides replaced by uronic acids (-->saccharopeptides). These saccharopeptides are surprisingly good substrates for alpha-2,3,-sialyltransferase and fucosyltransferase III. The enzymes transfer N-acetylneuraminic acid and fucose, respectively, onto these acceptor substrates, despite the far reaching alterations, regio- and stereospecifically in the expected manner to yield sialyl-Lewis(a)-saccharopeptides.

On the preparative use of recombinant pig alpha(1-3)galactosyl-transferase

A series of non-natural N-acyl derivatives of lactosamine is incubated with recombinant alpha(1-3)galactosyl-transferase and UDP-galactose. The enzyme shows a high promiscuity towards the non-natural acceptors. It selectively transfers a galactose unit onto the 3-OH group of the terminal beta-linked galactose in an alpha-mode to give an array of linear-B trisaccharides.

Enzymatic synthesis of sialyl-Lewis(a)-libraries with two non-natural monosaccharide units

A series of sialylated type-I sugars, which have the natural N-acetyl group of the glucosamine moiety replaced by a wide range of amides, is incubated with recombinant fucosyl-transferase III and non-natural guanosine-diphosphate activated donor-sugars. Surprisingly, the enzyme tolerates the simultaneous alterations on the donor and acceptor to form a wide array of sialyl-Lewis(a)-analogues.