Mechanisms for enforced general acid catalysis of the addition of thiol anions to acetaldehyde

Gilbert, Hiram F.; Jencks, William P.

doi:10.1021/ja00466a029

Cited by 56 publications

(33 citation statements)

References 17 publications

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“…1C). The decrease in magnitude for binding of the point mutants probably reflects the non-additivity observed in such experiments due to entropic considerations of quasi-independent but physically linked binding sites (40).…”

Section: Human E2 Paralogs Bind Uba1 Through Conserved Motif-mentioning

confidence: 89%

E1-E2 Interactions in Ubiquitin and Nedd8 Ligation Pathways

Tokgöz

Siepmann

Streich

et al. 2012

Journal of Biological Chemistry

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Background: Ubiquitin carrier protein (E2) recognition by ubiquitin activating enzyme (E1) defines fidelity in subsequent conjugation reactions. Results: E2 transthiolation kinetics identify structural features defining the specificity of E1-E2 binding. Conclusion: E2 paralogs contain a conserved E1 binding motif, and the E1 ␤-grasp domain is a specificity filter for E2 binding. Significance: This defines structural features determining ubiquitin conjugation fidelity.

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Section: Human E2 Paralogs Bind Uba1 Through Conserved Motif-mentioning

confidence: 89%

E1-E2 Interactions in Ubiquitin and Nedd8 Ligation Pathways

Tokgöz

Siepmann

Streich

et al. 2012

Journal of Biological Chemistry

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“…Thus in the equilibrated mixed disulfide state, the Asp-26 carboxylate will serve to remove the Cys-35 thiol proton facilitating the attack on the mixed disulfide linkage. Support for this model comes from the solvent kinetic isotope effect observed in the Gilbert and Jencks study on the thiolate reaction with acetaldehyde (10). The magnitude of the isotope effect depends of the proton source.…”

Section: Mechanism Of Asp-26-dependent Protonmentioning

confidence: 96%

The Role of the Buried Aspartate of Escherichia coliThioredoxin in the Activation of the Mixed Disulfide Intermediate

LeMaster

Springer

Ünkefer

1997

Journal of Biological Chemistry

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The structurally homologous protein disulfide isomerases and thioredoxins exhibit a 10 5 variation of redox equilibria. It is demonstrated that the kinetic distinction among these protein family members lies primarily in the rate of breakdown of the mixed disulfide intermediate. The conserved buried acid group serves as a proton transfer catalyst for the buried active site cysteine in the formation and breakdown of the mixed disulfide. The reduction rate of Escherichia coli thioredoxin by dithiothreitol is directly proportional to the fraction of Asp-26 in the protonated form over the pH range of 6 -9. The kinetic role of Asp-26 is further probed via differential solvent kinetic isotope effect measurements versus a D26N variant. The differential solvent isotope effect of 0.6 is consistent with a direct proton donation to the thiolate leaving group (Cys-35) via an enforced general acid catalysis by trapping mechanism. Such a donation necessitates a structural rearrangement as these two buried side chains are separated by 6 Å in both the oxidized and reduced forms of the protein.Despite substantial sequence variability, the mammalian and bacterial protein disulfide isomerases, as well as the ubiquitous thioredoxins, appear to share a common structural motif (1) and are generally assumed to utilize a common enzymatic mechanism to achieve their accelerated reactivities in both dithiol oxidation and disulfide reduction (Fig. 1). Although the conformation of the active sites are markedly similar (2, 3), there is a 10 5 -fold variation in redox equilibria between Escherichia coli thioredoxin (EЈ 0 ϭ Ϫ260 mV (4)) and the E. coli protein disulfide isomerase protein DsbA (EЈ 0 ϭ Ϫ0.1 mV (5)). Within the thioredoxin/protein disulfide isomerase family the active site disulfide (-CXXC-) sequence spans the top of the first turn of an a-helix (the a 2 helix in E. coli thioredoxin) with the sulfur of the first cysteine exposed for reaction with exogenous thiols and disulfides while the second cysteine is buried within the protein interior. Much of the research into the mechanism has focused on the reactions of the solvent exposed thiol (Cys-32 in E. coli thioredoxin). Particularly noteworthy is the quantitative correlation between the redox potential and the pK of this solvent exposed thiol observed for a series of protein disulfide isomerase variants (6). This correlation is also proposed to extend to the E. coli thioredoxin (7).Since K eq equals (k 1 /k Ϫ1 )⅐(k 2 /k Ϫ2 ) for Fig. 1, the large differences in redox equilibria between the protein disulfide isomerases and the thioredoxins must be manifested in the individual rate constants. E. coli thioredoxin exhibits a k 1 reaction rate of 120 M Ϫ1 s Ϫ1 with oxidized glutathione under the conditions reported for human PDI 1 ␣ domain in Fig. 1 (8). Given the similarity in the rate constants observed for this step, the major difference in kinetics exhibited by these two enzymes does not lie primarily in the reaction of the protein thiol with the target disulfide substrate. Hence,...

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“…A-+ HN + C( 3 ) rection this corresponds to general base catalysis of amine attack. The Brvnsted plot for the acid-catalyzed cleavage of N-p-nitrophenylcarbamate (Figure 5) extends the data obtained previously by Johnson and Morrisons and shows that the rate constants for cationic and for neutral or anionic cat-…”

mentioning

confidence: 99%

Mechanism of cleavage of carbamate anions

Ewing¹,

Lockshon²,

Jencks³

1980

J. Am. Chem. Soc.

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Carbamates and monothiocarbamates of basic aliphatic amines undergo rate-determining C-N cleavage after a rapid equilibrium protonation step, as shown most directly by inverse solvent deuterium isotope effects of kD/kH = 3.6-4.8 for 0.0-and 0,s-N-n-butylcarbamates and by rapid acid-catalyzed exchange of the N H proton of n-BuNHCOS-with k e x c h = 5 X lo7 M-I s-I. The lifetimes of substituted N-protonated carbamates have been estimated to range down to <1O-Io s. It is concluded that general acid catalysis of the cleavage of carbamates of weakly basic anilines ( a = 0.84) occurs through an enforced preassociation mechanism with hydrogen bonding to the leaving protonated nitrogen atom and C-N cleavage in the rate-determining step. There is more proton transfer in the transition state (larger a ) and a smaller / ?I, with more basic amines and upon substitution of sulfur for oxygen. The low pK, values of N-protonated carbamates and monothiocarbamates illustrate the strong electron-accepting ability of -COO-and -COS-.

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Mechanisms for enforced general acid catalysis of the addition of thiol anions to acetaldehyde

Cited by 56 publications

References 17 publications

E1-E2 Interactions in Ubiquitin and Nedd8 Ligation Pathways

E1-E2 Interactions in Ubiquitin and Nedd8 Ligation Pathways

The Role of the Buried Aspartate of Escherichia coliThioredoxin in the Activation of the Mixed Disulfide Intermediate

Mechanism of cleavage of carbamate anions

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