How metal substitution affects the enzymatic activity of catechol-o-methyltransferase.

Manuel Sparta,Anastassia N Alexandrova,Roland Seifert

doi:10.1371/journal.pone.0047172

Manuel Sparta, Anastassia N Alexandrova + Show 1 more

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https://doi.org/10.1371/journal.pone.0047172

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Journal: PloS one	Publication Date: Oct 8, 2012
Citations: 53	License type: CC BY 4.0

Affiliation: University of California, Los Angeles

Abstract

Catechol-O-methyltransferase (COMT) degrades catecholamines, such as dopamine and epinephrine, by methylating them in the presence of a divalent metal cation (usually Mg(II)), and S-adenosyl-L-methionine. The enzymatic activity of COMT is known to be vitally dependent on the nature of the bound metal: replacement of Mg(II) with Ca(II) leads to a complete deactivation of COMT; Fe(II) is slightly less than potent Mg(II), and Fe(III) is again an inhibitor. Considering the fairly modest role that the metal plays in the catalyzed reaction, this dependence is puzzling, and to date remains an enigma. Using a quantum mechanical / molecular mechanical dynamics method for extensive sampling of protein structure, and first principle quantum mechanical calculations for the subsequent mechanistic study, we explicate the effect of metal substitution on the rate determining step in the catalytic cycle of COMT, the methyl transfer. In full accord with experimental data, Mg(II) bound to COMT is the most potent of the studied cations and it is closely followed by Fe(II), whereas Fe(III) is unable to promote catalysis. In the case of Ca(II), a repacking of the protein binding site is observed, leading to a significant increase in the activation barrier and higher energy of reaction. Importantly, the origin of the effect of metal substitution is different for different metals: for Fe(III) it is the electronic effect, whereas in the case of Ca(II) it is instead the effect of suboptimal protein structure.

Highlights

Catechol-O-methyltransferase (COMT, EC 2.1.1.6) is an enzyme involved in the biology of pain, where its inhibition leads to greater pain sensitivity
We focus on just the catalytic process, with the purpose of determining the extent to which the metal-dependent behavior of COMT could be explained by the relative facility of the catalytic process itself
In order to test the accuracy of the quantum mechanical (QM)/DMD method for modeling of COMT and its derivatives, we first simulated the native Mg(II) form of the enzyme with the bound 3,5dinitrocatechol inhibitor and SAM

Summary

Introduction

Catechol-O-methyltransferase (COMT, EC 2.1.1.6) is an enzyme involved in the biology of pain, where its inhibition leads to greater pain sensitivity. COMT is a common target for drugs that alter its activity and regulate the level of catecholamines in the body. The enzyme promotes the transfer of the methyl group from the cofactor, S-adenosyl-L-methionine (SAM), to one of the hydroxyl groups of catechol, or substituted catechol, in the presence of a divalent metal cation (Scheme S1) [3]. Mg(II) can be substituted with Co(II), Mn(II), Zn(II), Cd(II), Fe(II), Fe(III), Ni(II), and Sn(II), [3] but metal replacement sometimes leads to unexplainable changes in the enzyme activity. Co(II) and Mn(II), on the other hand, are most effective in catalysis [3] It is not fully understood whether the change in activity upon metal substitution is due to the catalytic process itself, or other factors. We focus on just the catalytic process, with the purpose of determining the extent to which the metal-dependent behavior of COMT could be explained by the relative facility of the catalytic process itself

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