Solvolysis of D-glucopyranosyl derivatives in mixtures of ethanol and 2,2,2-trifluoroethanol

Sinnott, Michael L.; Jencks, William P.

doi:10.1021/ja00526a043

Cited by 141 publications

(158 citation statements)

References 10 publications

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“…In the absence of direct evidence of a viable covalent intermediate, an alternative mechanism, termed as an S N i "internal return," has been proposed invoking an oxocarbenium ion-like transition state, with phospho-sugar bond breakage and glycosidic bond formation occurring in a concerted, but necessarily asynchronous manner, on the same face of the sugar (52,53). This mechanism was first proposed nearly 30 years ago to describe anomalous results seen in the solvolysis of glucopyransoyl fluorides where a kinetically unimolecular reaction (S N 1-like) resulted in retention of configuration of the sugar (S N 2-like) (54).…”

Section: Resultsmentioning

confidence: 99%

Structural and Enzymatic Analysis of MshA from Corynebacterium glutamicum

Vetting

Frantom

Blanchard

2008

Journal of Biological Chemistry

114

192

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The glycosyltransferase termed MshA catalyzes the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to 1-Lmyo-inositol-1-phosphate in the first committed step of mycothiol biosynthesis. The structure of MshA from Corynebacterium glutamicum was determined both in the absence of substrates and in a complex with UDP and 1-L-myo-inositol-1-phosphate. MshA belongs to the GT-B structural family whose members have a two-domain structure with both domains exhibiting a Rossman-type fold. Binding of the donor sugar to the C-terminal domain produces a 97°rotational reorientation of the N-terminal domain relative to the C-terminal domain, clamping down on UDP and generating the binding site for 1-Lmyo-inositol-1-phosphate. The structure highlights the residues important in binding of UDP-N-acetylglucosamine and 1-L-myo-inositol-1-phosphate. Molecular models of the ternary complex suggest a mechanism in which the ␤-phosphate of the substrate, UDP-N-acetylglucosamine, promotes the nucleophilic attack of the 3-hydroxyl group of 1-L-myo-inositol-1-phosphate while at the same time promoting the cleavage of the sugar nucleotide bond.

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Section: Resultsmentioning

confidence: 99%

Structural and Enzymatic Analysis of MshA from Corynebacterium glutamicum

Vetting

Frantom

Blanchard

2008

Journal of Biological Chemistry

114

192

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“…45, 50, 52, and 56). Although such reactions are not without chemical precedent (57,58), they are exceedingly difficult to demonstrate experimentally. Here we have unveiled, for the first time, the donor subsite interactions of the GT-B class of retaining UDPsugar glycosyltransferase.…”

Section: Discussionmentioning

confidence: 99%

The Donor Subsite of Trehalose-6-phosphate Synthase

Gibson

Tarling

Roberts

et al. 2004

Journal of Biological Chemistry

106

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Trehalose is an unusual non-reducing disaccharide that plays a variety of biological roles, from food storage to cellular protection from environmental stresses such as desiccation, pressure, heat-shock, extreme cold, and oxygen radicals. It is also an integral component of the cell-wall glycolipids of mycobacteria. The primary enzymatic route to trehalose first involves the transfer of glucose from a UDP-glucose donor to glucose-6-phosphate to form ␣,␣-1,1 trehalose-6-phosphate. This reaction, in which the configurations of two glycosidic bonds are set simultaneously, is catalyzed by the glycosyltransferase trehalose-6-phosphate synthase (OtsA), which acts with retention of the anomeric configuration of the UDP-sugar donor. The classification of activated sugar-dependent glycosyltransferases into approximately 70 distinct families based upon amino acid sequence similarities places OtsA in glycosyltransferase family 20 (see afmb.cnrs-mrs.fr/CAZY/). The recent 2.4 Å structure of Escherichia coli OtsA revealed a two-domain enzyme with catalysis occurring at the interface of the twin ␤/␣/␤ domains. Here we present the 2.0 Å structures of the E. coli OtsA in complex with either UDP-Glc or the non-transferable analogue UDP-2-deoxy-2-fluoroglucose. Both complexes unveil the donor subsite interactions, confirming a strong similarity to glycogen phosphorylases, and reveal substantial conformational differences to the previously reported complex with UDP and glucose 6-phosphate. Both the relative orientation of the two domains and substantial (up to 10 Å) movements of an N-terminal loop (residues 9 -22) characterize the more open "relaxed" conformation of the binary UDP-sugar complexes reported here.

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“…Since evidence for a doubledisplacement mechanism has remained elusive for maltodextrin phosphorylase and galactosyltransferase, alternative mechanistic scenarios have been proposed [11,12,15,27,30,31]. One of these is the so-called internal return (S N i) mechanism of glycosyl transfer that assumes approach of the nucleophile towards the reactive carbon from the same side from where the leaving group departs [11,32]. The S N i mechanism of phosphorylase-catalysed glucosyl transfer to and from phosphate would require a highly dissociative (' exploded ' [33]) transition state, with electrostatic stabilization of the oxocarbenium ion provided mainly by the phosphate group from the front face.…”

Section: Kinetic Mechanism Of Trehalose Phosphorylasementioning

confidence: 99%

“…The S N i mechanism of phosphorylase-catalysed glucosyl transfer to and from phosphate would require a highly dissociative (' exploded ' [33]) transition state, with electrostatic stabilization of the oxocarbenium ion provided mainly by the phosphate group from the front face. A chemical precedent for the internal return mechanism is provided by studies of the trifluoroethanolysis of α--glucopyranosyl fluoride, a reaction that was shown to yield predominantly trifluoroethyl α--glucoside [32]. By analogy with the proposal made by Sinnott and Jencks [32], the essential feature of an S N i mechanism of phosphorylase action would be the following : the leaving group is effectively HO $ P-O# − :::::::H-OR, where ROH is the incoming nucleophile, and internal return occurs from within the ion pair by the recombination of the anomeric carbon and the leaving group on the oxygen of ROH to yield the α-configured product.…”

Section: Kinetic Mechanism Of Trehalose Phosphorylasementioning

confidence: 99%

“…A chemical precedent for the internal return mechanism is provided by studies of the trifluoroethanolysis of α--glucopyranosyl fluoride, a reaction that was shown to yield predominantly trifluoroethyl α--glucoside [32]. By analogy with the proposal made by Sinnott and Jencks [32], the essential feature of an S N i mechanism of phosphorylase action would be the following : the leaving group is effectively HO $ P-O# − :::::::H-OR, where ROH is the incoming nucleophile, and internal return occurs from within the ion pair by the recombination of the anomeric carbon and the leaving group on the oxygen of ROH to yield the α-configured product. Although such a mechanism is not widely observed in chemical reactions, an attractive component of a possible S N i mechanism for trehalose phosphorylase is the fact that it explains the strict requirement for a ternary complex, as well as bondforming and bond-cleaving steps that appear inherently coupled.…”

Section: Kinetic Mechanism Of Trehalose Phosphorylasementioning

confidence: 99%

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Fungal trehalose phosphorylase: kinetic mechanism, pH-dependence of the reaction and some structural properties of the enzyme from Schizophyllum commune

et al. 2001

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Initial-velocity measurements for the phospholysis and synthesis of α,α-trehalose catalysed by trehalose phosphorylase from Schizophyllum commune and product and dead-end inhibitor studies show that this enzyme has an ordered Bi Bi kinetic mechanism, in which phosphate binds before α,α-trehalose, and α--glucose is released before α--glucose 1-phosphate. The freeenergy profile for the enzymic reaction at physiological reactant concentrations displays its largest barriers for steps involved in reverse glucosyl transfer to -glucose, and reveals the direction of phospholysis to be favoured thermodynamically. The pH dependence of kinetic parameters for all substrates and the dissociation constant of -glucal, a competitive dead-end inhibitor against -glucose (K i l 0.3 mM at pH 6.6 and 30 mC), were determined. Maximum velocities and catalytic efficiencies for the forward and reverse reactions decrease at high and low pH, giving apparent pK values of 7.2-7.8 and 5.5-6.0 for two groups whose correct protonation state is required for catalysis. The pH dependences of k cat \K are interpreted in terms of

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Solvolysis of D-glucopyranosyl derivatives in mixtures of ethanol and 2,2,2-trifluoroethanol

Cited by 141 publications

References 10 publications

Structural and Enzymatic Analysis of MshA from Corynebacterium glutamicum

Structural and Enzymatic Analysis of MshA from Corynebacterium glutamicum

The Donor Subsite of Trehalose-6-phosphate Synthase

Fungal trehalose phosphorylase: kinetic mechanism, pH-dependence of the reaction and some structural properties of the enzyme from Schizophyllum commune

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