Sulfate group transfer between nitrogen and oxygen: evidence consistent with an open "exploded" transition state

Hopkins, Andrew; Day, R.; Williams, A. Stanley

doi:10.1021/ja00357a017

Cited by 46 publications

(52 citation statements)

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“…5b indicates very little OOS bond formation in the transition state. Furthermore, the effective charge on the phenolic oxygen is Ϫ0.67, in close agreement with the literature value (32). It should be noted that the leaving group used in the uncatalyzed studies was different from the current leaving group, and this could be contributing to the differences we have observed.…”

Section: Tively ‡supporting

confidence: 90%

“…A reasonable linear correlation was seen, and ␤ nuc was determined to be 0.33. This value is slightly higher than the value reported in the literature for the uncatalyzed reaction (32). The calculated effective charge on the phenolic oxygen in the transition state is Ϫ0.77 for the uncatalyzed reaction and Ϫ0.67 for the catalyzed reaction.…”

Section: Tively ‡contrasting

confidence: 51%

“…Fig. 5a shows the values for ␤ EQ and ␤ nuc from the literature giving a Leff ler's ␣ of 0.13 (0.23͞1.74) (32). This low value of Leff ler's ␣ indicates little change in the effective charge on the nucleophile, demonstrative of little nucleophilic participation (37,38).…”

mentioning

confidence: 97%

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Mechanistic studies of β-arylsulfotransferase IV

Chapman

Bryan

Wong

2003

Proc. Natl. Acad. Sci. U.S.A.

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Sulfotransferases are an important class of enzymes that catalyze the transfer of a sulfuryl group to a hydroxyl or amine moiety on various molecules including small-molecule drugs, steroids, hormones, carbohydrates, and proteins. They have been implicated in a number of disease states but remain poorly understood, complicating the design of specific, small-molecule inhibitors. A linear free-energy analysis in both the forward and reverse directions indicates that the transfer of a sulfuryl group to an aryl hydroxyl group catalyzed by ␤-arylsulfotransferase IV likely proceeds by a dissociative (sulfotrioxide-like) mechanism. Values for the Brønsted coefficients (␤ nuc and ␤lg) are ؉0.33 and ؊0.45, giving Leffler ␣ values of 0.19 and 0.61 for the forward and reverse reactions, respectively.sulfotransferase ͉ linear free energy ͉ mechanism S ulfotransferases (STs) are an important class of enzymes that catalyze the transfer of a sulfuryl group from 3Ј-phospho-adenosyl-5Ј-phosphosulfate (PAPS) to a hydroxyl or, less frequently, an amine to give the sulfated product and the cofactor byproduct 3Ј-phosphoadenosyl-5Ј-phosphate (PAP) (Fig. 1). They can be divided into two groups: the cytosolic STs and the membrane-associated STs. Cytosolic STs catalyze the sulfonation of xenobiotics for detoxification and hormones for regulation. Membrane-associated STs catalyze the sulfonation of proteins and carbohydrates for processes such as cellular signaling and modulation of receptor binding (1-9). Recent studies have implicated the STs in a number of disease states including entry of the herpes virus (10), entry of HIV (11, 12), chronic inf lammation (13), and various forms of cancer (1-9). For this reason there is considerable interest in the design of small-molecule inhibitors that are specific for a particular ST. Although a number of inhibitor designs and syntheses have been published, to date the inhibitors are relatively weak and have always been discovered through semirational methods because of the lack of a complete mechanistic picture (14).A number of structural and mechanistic studies have been carried out on STs. Crystal structures have been solved for estrogen ST (15), catecholamine ST (16), dopamine ST (17), hydroxysteroid ST (18), and the ST domain of heparan sulfate N-deacetylase͞N- . Sequence alignment data from these structures as well as other STs show there to be a great deal of homology at the amino acid level for certain residues near the active site. Furthermore, mutagenesis studies carried out on these conserved residues show several of them to be critical to enzyme function. One such study of estrogen ST using a bound vanadate indicates an in-line attack of PAPS by the steroid hydroxyl group (20). Moreover, early studies of ␤-arylsulfotransferase IV (␤-AST-IV) show a random, rapidly equilibrating bi-bi mechanism (21). In the kinase field, the transition state of a protein tyrosine kinase has been illuminated through the use of linear free-energy studies (22). This information then was used to design spec...

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Section: Tively ‡supporting

confidence: 90%

Section: Tively ‡contrasting

confidence: 51%

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Mechanistic studies of β-arylsulfotransferase IV

Chapman

Bryan

Wong

2003

Proc. Natl. Acad. Sci. U.S.A.

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“…As noted previously, the nonenzymatic isotope effects of ∼2% (1.02) for pNPP and pNPS suggest substantial bond cleavage in the transition state, 46, 52, 54 consistent with the body of work on phosphoryl and sulfuryl transfer that supports a loose transition state for these reactions. [25][26][27][28][29][30][31][32] The isotope effect for R166S AP-catalyzed hydrolysis of pNPP is reduced relative to that in solution, with a value of ∼1% (Table 3). As linear free energy relationships give values of β lg consistent with the same extent of bond cleavage for nonenzymatic and AP-catalyzed reactions of phosphate, phosphorothioate, and sulfate monoesters, 35, 36, 50, 51, 53 we suggest that the reduced isotope effect results from transition state interactions between the leaving group oxygen and the active site Zn 2+ ion (Scheme 1).…”

Section: Analysis Of Interactions With the Leaving Group Oxygen Atommentioning

confidence: 99%

Probing the Origin of the Compromised Catalysis of E. coli Alkaline Phosphatase in its Promiscuous Sulfatase Reaction

et al. 2007

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The catalytic promiscuity of E. coli alkaline phosphatase (AP) and many other enzymes provides a unique opportunity to dissect the origin of enzymatic rate enhancements via a comparative approach. Here we use kinetic isotope effects (KIEs) to explore the origin of the 10 9 -fold greater catalytic proficiency by AP for phosphate monoester hydrolysis relative to sulfate monoester hydrolysis. The primary 18 O KIEs for the leaving group oxygen atoms in the AP-catalyzed hydrolysis of pnitrophenyl phosphate (pNPP) and p-nitrophenylsulfate (pNPS) decrease relative to the values observed for nonenzymatic hydrolysis reactions. Prior linear free energy relationship results suggest that the transition states for AP-catalyzed reactions of phosphate and sulfate esters are 'loose' and indistinguishable from that in solution, suggesting that the decreased primary KIEs do not reflect a change in the nature of the transition state but rather a strong interaction of the leaving group oxygen atom with an active site Zn 2+ ion. Furthermore, the KIEs for the two reactions are identical within error, suggesting that the differential catalysis of these reactions cannot be attributed to differential stabilization of the leaving group. In contrast, AP perturbs the KIE for the nonbridging oxygen atoms in the reaction of pNPP but not pNPS, suggesting a differential interaction with the transferred group in the transition state. These and prior results are consistent with a strong electrostatic interaction between the active site bimetallo Zn 2+ cluster and one of the nonbridging oxygen atoms on the transferred group. We suggest that the lower charge density of this oxygen atom on a transferred sulfuryl group accounts for a large fraction of the decreased stabilization of the transition state for its reaction relative to phosphoryl transfer.

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“…In contrast, while there has been some significant work on the hydrolysis of sulfate esters (see e.g. 27,33,[36][37][38][39] and references cited therein, amongst others), comparatively less attention has been paid to this class of reaction, despite the fact that, like phosphate esters, sulfate esters are of critical biological importance, playing for instance roles in detoxification 40 , the biosynthesis of steroids 41 and cellular signaling 36 .…”

Section: Introductionmentioning

confidence: 99%

Theoretical Comparison ofp-Nitrophenyl Phosphate and Sulfate Hydrolysis in Aqueous Solution: Implications for Enzyme-Catalyzed Sulfuryl Transfer

Kamerlin

2011

J. Org. Chem.

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Both phosphoryl and sulfuryl transfer are ubiquitous in biology, being involved in a wide range of processes, ranging from cell division to apoptosis. Additionally, it is becoming increasingly clear that enzymes that can catalyze phosphoryl transfer can often cross-catalyze sulfuryl-transfer (and vice versa).However, while there have been extensive experimental and theoretical studies performed on phosphoryl transfer, the body of available research on sulfuryl transfer is comparatively much smaller.The present work presents a direct theoretical comparison of p-nitrophenyl phosphate and sulfate monoester hydrolysis, both of which are considered prototype systems for probing phosphoryl and sulfuryl transfer respectively. Specifically, free energy surfaces have been generated using density functional theory, by initial geometry optimization in PCM using the 6-31+G* basis set and the B3LYP density functional, followed by single point calculations using the larger 6-311+G** basis set and the COSMO continuum model. The resulting surfaces have been then used to identify the relevant transition states, either by further unconstrained geometry optimization, or from the surface itself where possible.Additionally, configurational entropies were evaluated using a combination of the quasiharmonic approximation and the restraint release approach and added to the calculated activation barriers as a correction. Finally, the overall activation entropy was estimated by approximating the solvent contribution to the total activation entropy using the Langevin dipoles solvation model. We have reproduced both the experimentally observed activation barriers and the observed trend in the activation entropies with reasonable accuracy, as well providing a comparison of calculated and observed 15 N and 18 O kinetic isotope effects. We demonstrate that, counterintuitively, the hydrolysis of the p-nitrophenyl sulfate proceeds through a more expa show that the solvation effects upon moving from the ground state to the transition state are quite different for both reactions, suggesting that the enzymes that catalyze these reactions would need active 4 sites with quite different electrostatic preorganization for the efficient catalysis of either reaction (despite which many enzymes can catalyze both phosphoryl and sulfuryl transfer). We believe that such a comparative study is an important foundation for understanding the molecular basis for phosphatesulfate cross promiscuity within members of the alkaline phosphatase superfamily.

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Sulfate group transfer between nitrogen and oxygen: evidence consistent with an open "exploded" transition state

Cited by 46 publications

References 1 publication

Mechanistic studies of β-arylsulfotransferase IV

Mechanistic studies of β-arylsulfotransferase IV

Probing the Origin of the Compromised Catalysis of E. coli Alkaline Phosphatase in its Promiscuous Sulfatase Reaction

Theoretical Comparison ofp-Nitrophenyl Phosphate and Sulfate Hydrolysis in Aqueous Solution: Implications for Enzyme-Catalyzed Sulfuryl Transfer

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