Electrostatic attraction by surface charge does not contribute to the catalytic efficiency of acetylcholinesterase.

Shafferman, Avigdor; Ordentlich, Arie; Barak, Dov; Kronman, Chanoch; Ber, Rosalie; Bino, Tamar; Ariel, Naomi; Osman, Roman; Velan, Baruch

doi:10.1002/j.1460-2075.1994.tb06650.x

Cited by 94 publications

(60 citation statements)

References 45 publications

(45 reference statements)

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“…Using the electrostatic flux, we have shown that a seven-residue mutant of human acetylcholinesterase, which shows a much-reduced isopotential surface, still exhibits a substantial electrostatic attraction for acetylcholine near the entrance to the active-site gorge , in agreement with the experimental observations and theoretical calculations based on Brownian dynamics (Antosiewicz et al, 1995). The results of our approach contrast with the inferences drawn by Shafferman et al (1994) from viewing the reduction of a single isopotential surface: They concluded that electrostatics does not play an important role in human acetylcholinesterase.…”

Section: Rationale For Electrostatic Fluxcontrasting

confidence: 96%

Backbone makes a significant contribution to the electrostatics of α/β‐barrel proteins

et al. 1997

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The electrostatic properties of seven a/P-barrel enzymes selected from different evolutionary families were studied: triose phosphate isomerase, fructose-I ,6-bisphosphate aldolase, pyruvate kinase, mandelate racemase, trimethylamine dehydrogenase, glycolate oxidase, and narbonin, a protein without any known enzymatic activity. The backbone of the a/P-barrel has a distinct electrostatic field pattern, which is dipolar along the barrel axis. When the side chains are included in the calculations the general effect is to modulate the electrostatic pattern so that the electrostatic field is generally enhanced and is focused into a specific area near the active site. We use the electrostatic flux through a square surface near the active site to gauge the functionally relevant magnitude of the electrostatic field. The calculations reveal that in six out of the seven cases the backbone itself contributes greater than 45% of the total flux. The substantial electrostatic contribution of the backbone correlates with the known preference of cu/P-barrel enzymes for negatively charged substrates.

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Section: Rationale For Electrostatic Fluxcontrasting

confidence: 96%

Backbone makes a significant contribution to the electrostatics of α/β‐barrel proteins

et al. 1997

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“…Y For acetylcholinesterase, a large number of mutations of charged residues was made, and these were shown to have little effect on the rate of substrate binding (7). This result was interpreted as evidence of lack of diffusion control and electrostatic steering.…”

Section: Electrostatic Steeringmentioning

confidence: 99%

Electrostatic steering and ionic tethering in enzyme–ligand binding: Insights from simulations

Wade

Gabdoulline

Lüdemann

et al. 1998

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

205

171

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To bind at an enzyme's active site, a ligand must diffuse or be transported to the enzyme's surface, and, if the binding site is buried, the ligand must diffuse through the protein to reach it. Although the driving force for ligand binding is often ascribed to the hydrophobic effect, electrostatic interactions also inf luence the binding process of both charged and nonpolar ligands. First, electrostatic steering of charged substrates into enzyme active sites is discussed. This is of particular relevance for diffusion-inf luenced enzymes. By comparing the results of Brownian dynamics simulations and electrostatic potential similarity analysis for triose-phosphate isomerases, superoxide dismutases, and ␤-lactamases from different species, we identify the conserved features responsible for the electrostatic substrate-steering fields. The conserved potentials are localized at the active sites and are the primary determinants of the bimolecular association rates. Then we focus on a more subtle effect, which we will refer to as ''ionic tethering.'' We explore, by means of molecular and Brownian dynamics simulations and electrostatic continuum calculations, how salt links can act as tethers between structural elements of an enzyme that undergo conformational change upon substrate binding, and thereby regulate or modulate substrate binding. This is illustrated for the lipase and cytochrome P450 enzymes. Ionic tethering can provide a control mechanism for substrate binding that is sensitive to the electrostatic properties of the enzyme's surroundings even when the substrate is nonpolar.

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“…A comprehensive mutagenesis study of human AChE was undertaken to analyze the kinetic contributions of seven surface anionic charges influencing the electric field of AChE (12). Those surface residues outside of the active center gorge had only a small influence on catalytic efficiency for both cationic and neutral substrates.…”

mentioning

confidence: 99%

Electrostatic Influence on the Kinetics of Ligand Binding to Acetylcholinesterase

Radić¹,

Kirchhoff

Quinn

et al. 1997

Journal of Biological Chemistry

210

248

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To explore the role that surface and active center charges play in electrostatic attraction of ligands to the active center gorge of acetylcholinesterase (AChE), and the influence of charge on the reactive orientation of the ligand, we have studied the kinetics of association of cationic and neutral ligands with the active center and peripheral site of AChE. Electrostatic influences were reduced by sequential mutations of six surface anionic residues outside of the active center gorge (Glu-84, Glu-91, Asp-280, Asp-283, Glu-292, and Asp-372) and three residues within the active center gorge (Asp-74 at the rim and Glu-202 and Glu-450 at the base). The peripheral site ligand, fasciculin 2 (FAS2), a peptide of 6.5 kDa with a net charge of ؉4, shows a marked enhancement of rate of association with reduction in ionic strength, and this ionic strength dependence can be markedly reduced by progressive neutralization of surface and active center gorge anionic residues. By contrast, neutralization of surface residues only has a modest influence on the rate of cationic m-trimethylammoniotrifluoroacetophenone (TFK ؉ ) association with the active serine, whereas neutralization of residues in the active center gorge has a marked influence on the rate but with little change in the ionic strength dependence. Brownian dynamics calculations for approach of a small cationic ligand to the entrance of the gorge show the influence of individual charges to be in quantitative accord with that found for the surface residues. Anionic residues in the gorge may help to orient the ligand for reaction or to trap the ligand. Bound FAS2 on AChE not only reduces the rate of TFK ؉ reaction with the active center but inverts the ionic strength dependence for the cationic TFK ؉ association with AChE. Hence it appears that TFK ؉ must traverse an electrostatic barrier at the gorge entry imparted by the bound FAS2 with its net charge of ؉4.

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Electrostatic attraction by surface charge does not contribute to the catalytic efficiency of acetylcholinesterase.

Cited by 94 publications

References 45 publications

Backbone makes a significant contribution to the electrostatics of α/β‐barrel proteins

Backbone makes a significant contribution to the electrostatics of α/β‐barrel proteins

Electrostatic steering and ionic tethering in enzyme–ligand binding: Insights from simulations

Electrostatic Influence on the Kinetics of Ligand Binding to Acetylcholinesterase

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