Domain Evolution in the α-Amylase Family

The available amino acid sequences of the α-amylase family (glycosyl hydrolase family 13) were searched to identify their domain B, a distinct domain that protrudes from the regular catalytic (β/α)₈-barrel between the strand β3 and the helix α3. The isolated domain B sequences were inspected visually and also analyzed by Hydrophobic Cluster Analysis (HCA) to find common features. Sequence analyses and inspection of the few available three-dimensional structures suggest that the secondary structure of domain B varies with the enzyme specificity. Domain B in these different forms, however, may still have evolved from a common ancestor. The largest number of different specificities was found in the group with structural similarity to domain B from Bacillus cereus oligo-1,6-glucosidase that contains an α-helix succeeded by a three-stranded antiparallel β-sheet. These enzymes are α-glucosidase, cyclomaltodextrinase, dextran glucosidase, trehalose-6-phosphate hydrolase, neopullulanase, and a few α-amylases. Domain B of this type was observed also in some mammalian proteins involved in the transport of amino acids. These proteins show remarkable similarity with (β/α)₈-barrel elements throughout the entire sequence of enzymes from the oligo-1,6-glucosidase group. The transport proteins, in turn, resemble the animal 4F2 heavy-chain cell surface antigens, for which the sequences either lack domain B or contain only parts thereof. The similarities are compiled to indicate a possible route of domain evolution in the α-amylase family. Received: 4 December 1996 / Accepted: 13 March 1997     

Application of click chemistry towards an efficient synthesis of 1,2,3-1H-triazolyl glycohybrids as enzyme inhibitors

An efficient synthesis of novel 1,2,3-1H-triazolyl glycohybrids with two or more than two sugar units or a chromenone moiety via copper-catalysed azide–alkyne cycloaddition (CuAAC), a 1,3-dipolar cycloaddition of glycosyl azides to 2,3-unsaturated alkynyl glycosides or propargyloxy coumarins is described. The synthesised glycohybrids were screened for their α-glucosidase, glycogen phosphorylase and glucose-6-phosphatase inhibitory activities. A few of the glycohybrids showed promising inhibitory activities against these enzymes.     

The role of the active site Zn in the catalytic mechanism of the GH38 Golgi α-mannosidase II: Implications from noeuromycin inhibition

Golgi α-mannosidase II (GMII) is a Family 38 glycosyl hydrolase involved in the eukaryotic N-glycosylation pathway in protein synthesis. Understanding of its catalytic mechanism has been of interest for the development of specific inhibitors that could lead to novel anti-metastatic or anti-inflammatory compounds. The active site of GMII has been characterized by structural studies of the Drosophila homologue (dGMII) and unusually contains a Zn atom which forms contacts with substrate analogues, stabilized catalytic intermediates, and other inhibitors observed in the active site. In this contribution, we analyze the structure of the sugar mimetic compound noeuromycin complexed with dGMII. Distortions of the conformation of this inhibitor, together with similar observations from other complexes, have permitted us to propose specific roles for the Zn atom in the chemical mechanism of catalysis of Family 38 glycosidase. Such insights have relevance to efforts to formulate novel, specific inhibitors of GMII.     

REACTION Of GLYCOSYL ISOTHIOCYNATES WITH 3-INDOLYLAMINOMETHYL-KETONE HYDROCHLORIDE

ABSTRACT

Reaction of glycosyl isothiocyanate 1a-c with 3-indolylaminomethyl-ketone hydrochloride(2) yielded glycosylthiourea derivatives 3a-c. Cyclodehydration of 3a-c with acetic anhydride afforded 5-(indol-3-yl)-2-[N-per-O-acetyl-D-glycopyranosyl)amino]thiazoles 4a-c. Deacetylation of 4a-c gave 5-(indol-3-yl)-2-[N-(D-glycopyranosyl) amino]thiazoles 5a-c.     

Thiosugar Nucleosides. Synthesis and Biological Activity of 1,3,4‐Thiadiazole,Thiazoline and Thiourea Derivatives of 5‐Thio‐d‐Glucose

New acylated 5‐thio‐β‐d‐glucopyranosylimino‐disusbstituted 1,3,4‐thiadiazols 8, and 11 were prepared, via spontaneous rearrangements, by cycloaddition of the glycosyl isothiocyanate 2 with the reactive intermediates 1‐aza‐2‐azoniaallene hexachloroantimonates 4 and 6, respectively. Reaction of 2 with aminoacetone or chloroethylamine afforded the acylated 5‐thio‐β‐d‐glucopyranosyl‐4‐imidazoline‐2‐thione nucleoside 16 and glucopyranosylamino‐2‐thiazoline derivative 18, respectively. Deblocking of 8, 11, 17 and 19 furnished the free nucleoside analogues 9, 12, 18 and 20, respectively. Analogously, treatment of 2 with chloroethylamine in the 1:2 ratio afforded the thioureylendisaccharide 21. No in vitro antiviral activity against HIV‐1, HIV‐2, human cytomegallovirus (HMCV), has been found for the new synthesized compounds.     

The behaviour of deoxyhexose trihaloacetimidates in selected glycosylations

Armed deoxyhexose glycosyl donors are very reactive and sometimes too uncontrollably activated in glycosylation reactions; yields can be thereby reduced, especially when unreactive glycosyl acceptors are involved. In this paper, the behaviour of a range of deoxyhexose trihaloacetimidate (trichloro- and N-phenyl trifluoro-) donors is compared in some selected glycosylations towards biologically relevant targets. The selected N-phenyl trifluoroacetimidates often afforded best results in terms of both donor synthesis and glycosylation yield.     

Environmentally benign and stereoselective formation of beta-mannosidic linkages utilizing 2,3-di-O-benzyl-4,6-O-benzylidene-protected mannopyranosyl phosphite and montmorillonite K-10

An environmentally benign and stereoselective beta-mannopyranosylation has been developed employing 4,6-O-benzylidene-protected mannopyranosyl diethyl phosphite as a glycosyl donor and montmorillonite K-10 as an activator.     

Zinc triflate-benzoyl bromide: a versatile reagent for the conversion of ether into benzoate protecting groups and ether glycosides into glycosyl bromides

A simple and efficient method is developed for the chemoselective one-pot conversion of ethers (benzyl, TBDMS and acetal) to the corresponding benzoates by zinc triflate-catalyzed deprotection and benzoylation by benzoyl bromide. In the same reaction, methyl or p-methoxyphenyl glycosides are converted into glycosyl bromides that are useful in glycosylation reactions.     

Biosynthesis of O-antigens: genes and pathways involved in nucleotide sugar precursor synthesis and O-antigen assembly

The O-antigen is an important component of the outer membrane of Gram-negative bacteria. It is a repeat unit polysaccharide and consists of a number of repeats of an oligosaccharide, the O-unit, which generally has between two and six sugar residues. O-Antigens are extremely variable, the variation lying in the nature, order and linkage of the different sugars within the polysaccharide. The genes involved in O-antigen biosynthesis are generally found on the chromosome as an O-antigen gene cluster, and the structural variation of O-antigens is mirrored by genetic variation seen in these clusters. The genes within the cluster fall into three major groups. The first group is involved in nucleotide sugar biosynthesis. These genes are often found together in the cluster and have a high level of identity. The genes coding for a significant number of nucleotide sugar biosynthesis pathways have been identified and these pathways seem to be conserved in different O-antigen clusters and across a wide range of species. The second group, the glycosyl transferases, is involved in sugar transfer. They are often dispersed throughout the cluster and have low levels of similarity. The third group is the O-antigen processing genes. This review is a summary of the current knowledge on these three groups of genes that comprise the O-antigen gene clusters, focusing on the most extensively studied E. coli and S. enterica gene clusters.     

Structure and serological characterization of the O-antigen of Proteus mirabilis O18 with a phosphocholine-containing oligosaccharide phosphate repeating unit

A phosphorylated, choline-containing polysaccharide was obtained by O-deacylation of the lipopolysaccharide (LPS) of Proteus mirabilis O18 by treatment with aqueous 12% ammonia, whereas hydrolysis with dilute acetic acid resulted in depolymerisation of the polysaccharide chain by the glycosyl phosphate linkage. Treatment of the O-deacylated LPS with aqueous 48% hydrofluoric acid cleaved the glycosyl phosphate group but, unexpectedly, did not affect the choline phosphate group. The polysaccharide and the derived oligosaccharides were studied by NMR spectroscopy, including 2D 1H,1H COSY, TOCSY, ROESY, 1H,13C HMQC and HMQC-TOSCY experiments, along with chemical methods, and the following structure of the pentasaccharide phosphate repeating unit was established: [carbohydrate structure in text] Where ChoP=Phosphocoline Immunochemical studies of the LPS, O-deacylated LPS and partially dephosphorylated pentasaccharide using rabbit polyclonal anti-P. mirabilis O18 serum showed the importance of the glycosyl phosphate group in manifesting the serological specificity of the O18-antigen.