L-Fucose isomerase

L-Fucose isomerase catalyzes the interconversion of L-fucose to L-fuculose and o-arabinose to D-ribulose. It has neither sequence nor structural similarity with the other aldose-ketose isomerases. A crystal structure of the E. coli enzyme with an L-fucitol bound in the active site shows that the active site is located in a 20 A deep pocket, at the bottom of which is a single Mn ion. Mn is bound to Oi and O2 of L-fucitol the side chains of a monodentate Glu-337, a bidentate Asp-361 (with long bonds to both oxygens), His-528 and a water molecule. ... 

Enzymic reactions with D-galactose oxidase or L-fucose isomerase were used for identification of the monosaccharide isolated after degradation of the esters. 

While DHAP aldolases produce ketose derivatives, access to biologically important and structurally more diverse aldose isomers is achievable by use of enzymatic ketol isomerase interconversions. For this purpose, we had previously shown that L-rhamnose isomerase (Rhal E.C. 5.3.1.14) and L-fucose isomerase (Fuel E.C. 5.3.1.3) from E. coli display a relaxed substrate tolerance. Both enzymes convert sugars and their derivatives with distinct stereopreference at C2 and common (3R)-OH configuration, but tolerate alterations in configuration or substitution pattern at subsequent positions of the chain (Scheme 2.2.5.5) [11, 12]. 

These enzymes vary widely in secondary and tertiary structure.1273 Mannose-6-phosphate isomerase is a 45 kDa Zn2+-containing monomer. The larger 65 kDa L-fucose isomerase, which also acts on D-arabinose, is a hexameric Mn2+-dependent enzyme.1273 L-Arabinose isomerase of E. coli, which interconverts arabinose and L-ribulose, is a hexamer of 60-kDa subunits128 while the D-xylose isomerase of Streptomyces is a tetramer of 43-kDa subunits.129 The nonenzymatic counterpart of the isomerization catalyzed by the enzyme is the base-catalyzed Lobry deBruyn-Alberda van Ekenstein transformation (Eq. 13-25).130... 

Fructose bisphosphate aldolases 699 Fructose 6-phosphate 535, 693s Fructose 6-phosphate kinase 656 Fructose-1,6-bisphosphatase 645 Fructose-2,6-bisphosphatase 646 Fruit fly. See Drosophilia melanogaster Fucose (Fuc) 165s L-Fucose isomerase 693 Fucosyltransferase 184 Fucoxanthin 22... 

On the basis of the X-ray structure of L-fucose isomerase of Escherichia coli, it has been suggested that this Mn -dependent enzyme acts via a metal ion-stabilised enediolate pathway, similar to Zn" catalysis of dihydroxyacetone enolisation, but the evidence so far is exclusively structural. 

We describe here the enzymological characteristics and application of isomerases, especially D-xylose (glucose) isomerase, phosphoglucose isomerase, triose phosphate isomerase, L-rhamnose isomerase, L-fucose isomerase, maleate cis-trans isomerase, and unsaturated fatty acid cis-trans isomerase. N-Acetyl-D-glucosamine 2-epimerase is not an isomerase, but for convenience we will also describe the characteristics and use of the enzyme because this section deals with sugar-metabolizing enzymes. 

Seemann and Schulz[2551 determined the three-dimensional structure of L-fucose isomerase from E. coli, a hexamer from a subunit with a molecular mass of 64 976 Da. The enzyme shows no structural similarity to any other aldose-ketose isomerases analyzed thus far. However, Seemann and Schulz, on the basis of the tertiary structure, suggested that the L-fucose isomerase reaction proceeds through an ene-diol intermediate [255l... 

Fessner et al.[256] developed an efficient method for the synthesis of L-fucose analogs modified at the nonpolar terminus by means of L-fucose isomerase and l-fuculose 1-phosphate aldolase from E. coli. Various L-fucose analogs bearing linear or branched aliphatic side chains were prepared in about 30% overall yield with hydroxyaldehyde precursors and dihydroxyacetone phosphate as the starting materials (Fig. 17-32). 

Figure 17-32. Enzymatic synthesis of L-fucose analogs with L-fucose 1-phosphate aldolase (FucA), phosphatase (P ase), and L-fucose isomerase (Fuel). Reprinted from Fessner et al.l2561.

Short syntheses of L-fucose analogues have been achieved (3 enzymatic steps) by aldol condensation of DHAP with various a-hydroxyaldehyde derivatives (using L-fuculose phosphate aldolase), followed by phosphate hydrolysis (alkaline phosphatase) and subsequent ketol isomerization (L-fucose isomerase). Selective C-labelling of thymidine in all positions of the 2 -deoxyribose ring has been achieved using an aldolase-catalysed reaction with appropriately C-labelled DHAP/acetaldehyde substrates. The labelled sugar was then converted... 

Several rare ketose 1-phosphates have been obtained by use of L-rhamnulose kinase on the corresponding ketoses which were, in turn, available by isomerization of the appropriate 2R- or 25-aldoses (D-ribose, L-lyxose, L-mannose, L-talose, D-glucose, D-allose, L-rhamnose, L-fucose) with L-rhamnose- or L-fucose-isomerase, respectively. P-L-Fucose 1-phosphate and the thermodynamically less stable p-anomer of GDP-fucose were accessible by use of enzymatic processes. A new, simple, chemical preparation of rhamnulose 1-phosphate from L-rhamnose is outlined in Scheme 5. ... 

Keywords Aldose ketol isomerEises, Enzymatic isomerisation, L-Fucose isomerase, D-Glucose (D-Xylose) isomerase. Non-natural substrates, L-RhEunnose isomerase... 

These enzymes, in particular o-xylose isomerase (o-glucose isomerase, EC 5.3.1.5) and L-fucose isomerase (EC 5.3.1.3), have attracted considerably more attention in terms of synthetic applicability, as compared with the epimerases. 

Schemes, a Shaded ribbon presentation of D-xylose (D-glucose) isomerase (EC 5.3.1.5) [61 a] with open-chain D-xylose/xylulose (capped sticks) coordinated to two metal ions in the active site (left) and L-fucose isomerase (EC 5.3.1.3) [94] with L-fucose and one metal ion (right), b Detail of the active site of D-xylose isomerase with histidine coordinating 0-5 of D-xylose and the two metal ions interacting with 0-1,0-2 and 0-4 of the substrate, c Detail of the active site of D-fucose isomerase with the metal ion coordinating 0-1 and 0-2 of the substrate... 

Very interesting applications of the preparative potential of microbial ketol isomerases were reported by Fessner and co-workers, who gained access to preparative amounts of L-rhamnose isomerase (EC 5.3.1.14) as well as L-fucose isomerase (EC 5.3.1.3) from E. colihy cloning and over-expression [95]. In this way they were able to convert (Scheme 34) a variety of d- and L-pentoses and -hex-oses into the corresponding 2-ketoses, such as L-mannose (111) (to L-fructose, 113), D-gulose (114) (to D-sorbose, 8) and D-allose (22) (to o-psicose, 10), to mention just a few. 

In context with a project aimed at structure-activity relationships of sialyl Lewis X epitope analogues, a range of new L-fucose derivatives with increased hydrophobicities of the C-5 substituents, such as compounds 124 and 126, was recently synthesised [100] employing Fessner s proven L-fuculose 1-phosphate aldolase/L-fucose isomerase protocol (Scheme 38). 

Currently, about ten sugar ketol isomerases are known (3), most of them produced from more than one known source. Similar to o-xylose isomerase and l-fucose isomerase, many of them are dependent on divalent cations, and some have not even been investigated in much detail at all. None has gained even a small fraction of the interest that has been paid to o-xylose isomerase due to its long known industrial importance. L-Fucose isomerase, yet another example, is one of a very few isomerases of current noteable synthetic importance. 

Arabinose Isomerases.—The activity of a D-arabinose isomerase (L-fucose isomerase) obtained from Klebsiella aerogenes was inhibited by tris and its analogues, which had no action on the L-arabinose isomerase present. ... 

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