The Organomercurial Lyase<scp>Mer</scp><scp>B</scp>

Cited by 5 publications

(6 citation statements)

References 51 publications

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“…(RC607) MerB2, and Clostridium butyricum MerB2) carry a Ser residue instead of Asp in their catalytic triad. Significantly, recent studies showed that the presence of a Ser residue in the active site substantially reduces the catalytic activity as well as the substrate specificity of these four MerB2 variants. − However, the mechanism by which these serine-containing organomercurial lyases (MerB2) cleave the Hg–C bonds of organomercurials has not been studied yet. In this context, therefore, it is beneficial to develop chemistry between [S 2 ]-donor ligands with various MeHg + compounds (such as ionic [MeHg]BF 4 , MeHgCl, and MeHgI) which may help in understanding the mechanism of detoxification of MeHg + by microorganisms.…”

Section: Introductionmentioning

confidence: 99%

Activation of the Hg–C Bond of Methylmercury by [S₂]-Donor Ligands

et al. 2017

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Here we report that [S]-donor ligands Bmm, Bmm, and Bme bind rapidly and reversibly to the mercury centers of organomercurials, RHgX, and facilitate the cleavage of Hg-C bonds of RHgX to produce stable tetracoordinated Hg(II) complexes and RHg. Significantly, the rate of cleavage of Hg-C bonds depends critically on the X group of RHgX (X = BF, Cl, I) and the [S]-donor ligands used to induce the Hg-C bonds. For instance, the initial rate of cleavage of the Hg-C bond of MeHgI induced by Bme is almost 2-fold higher than the initial rate obtained by Bmm or Bmm, indicating that the spacer between the two imidazole rings of [S]-donor ligands plays a significant role here in the cleavage of Hg-C bonds. Surprisingly, we noticed that the initial rate of cleavage of the Hg-C bond of MeHgI induced by Bme (or Bmm) is almost 10-fold and 100-fold faster than the cleavage of Hg-C bonds of MeHgCl and [MeHg]BF respectively, under identical reaction conditions, suggesting that the Hg-C bond of [MeHg]BF is highly inert at room temperature (21 °C). We also show here that the nature of the final stable cleaved products, i.e. Hg(II) complexes, depends on the X group of RHgX and the [S]-donor ligands. For instance, the reaction of Bmm with MeHgCl (1:1 molar ratio) afforded the formation of the 16-membered metallacyclic dinuclear mercury compound (Bmm)HgCl, in which the two Cl atoms are located inside the ring, whereas due to the large size of the I atom, a similar reaction with MeHgI yielded polymeric [(Bmm)HgI]·(MeHgI). However, the treatment of Bmm with ionic [RHg]BF led to the formation of the tetrathione-coordinated mononuclear mercury compound [(Bmm)Hg](BF), where BF serves as a counteranion.

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Section: Introductionmentioning

confidence: 99%

Activation of the Hg–C Bond of Methylmercury by [S₂]-Donor Ligands

et al. 2017

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“…The key catalytic roles for C96, C159, and D99 are supported by the fact that the two cysteine residues are conserved in all known variants of MerB and the aspartic acid is conserved in all but four of the known variants [ Bacillus megaterium MerB2, Bacillus subtillis MerB2, Bacillus sp. (RC607) MerB2, and Clostridium butyricum MerB2], in which the D99 is replaced with a serine residue . Although these four serine-containing MerB variants are derived from different organisms, they have 100% amino acid sequence identity so they are in fact identical proteins.…”

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confidence: 99%

Structural and Biochemical Characterization of a Copper-Binding Mutant of the Organomercurial Lyase MerB: Insight into the Key Role of the Active Site Aspartic Acid in Hg–Carbon Bond Cleavage and Metal Binding Specificity

Wahba

Lecoq²,

Stevenson

et al. 2016

Biochemistry

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In bacterial resistance to mercury, the organomercurial lyase (MerB) plays a key role in the detoxification pathway through its ability to cleave Hg-carbon bonds. Two cysteines (C96 and C159; Escherichia coli MerB numbering) and an aspartic acid (D99) have been identified as the key catalytic residues, and these three residues are conserved in all but four known MerB variants, where the aspartic acid is replaced with a serine. To understand the role of the active site serine, we characterized the structure and metal binding properties of an E. coli MerB mutant with a serine substituted for D99 (MerB D99S) as well as one of the native MerB variants containing a serine residue in the active site (Bacillus megaterium MerB2). Surprisingly, the MerB D99S protein copurified with a bound metal that was determined to be Cu(II) from UV-vis absorption, inductively coupled plasma mass spectrometry, nuclear magnetic resonance, and electron paramagnetic resonance studies. X-ray structural studies revealed that the Cu(II) is bound to the active site cysteine residues of MerB D99S, but that it is displaced following the addition of either an organomercurial substrate or an ionic mercury product. In contrast, the B. megaterium MerB2 protein does not copurify with copper, but the structure of the B. megaterium MerB2-Hg complex is highly similar to the structure of the MerB D99S-Hg complexes. These results demonstrate that the active site aspartic acid is crucial for both the enzymatic activity and metal binding specificity of MerB proteins and suggest a possible functional relationship between MerB and its only known structural homologue, the copper-binding protein NosL.

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“…46 In these four strains, the bacteria express two MerB proteins from their mer operon. The first, designated MerB1, contains the three catalytic residues corresponding to C96, D99, and C159 in E. coli MerB, but the second, designated MerB2, contains a serine residue in the position of the aspartic acid residue (D99), in addition to the two cysteine residues.…”

Section: Discussionmentioning

confidence: 99%

Structural and Biochemical Characterization of Organotin and Organolead Compounds Binding to the Organomercurial Lyase MerB Provide New Insights into Its Mechanism of Carbon–Metal Bond Cleavage

et al. 2017

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The organomercurial lyase MerB has the unique ability to cleave carbon–Hg bonds, and structural studies indicate that three residues in the active site (C96, D99, and C159 in E. coli MerB) play important roles in the carbon–Hg bond cleavage. However, the role of each residue in carbon–metal bond cleavage has not been well-defined. To do so, we have structurally and biophysically characterized the interaction of MerB with a series of organotin and organolead compounds. Studies with two known inhibitors of MerB, dimethyltin (DMT) and triethyltin (TET), reveal that they inhibit by different mechanisms. In both cases the initial binding is to D99, but DMT subsequently binds to C96, which induces a conformation change in the active site. In contrast, diethyltin (DET) is a substrate for MerB and the SnIV product remains bound in the active site in a coordination similar to that of HgII following cleavage of organomercurial compounds. The results with analogous organolead compounds are similar in that trimethyllead (TML) is not cleaved and binds only to D99, whereas diethyllead (DEL) is a substrate and the PbIV product remains bound in the active site. Binding and cleavage is an exothermic reaction, while binding to D99 has negligible net heat flow. These results show that initial binding of organometallic compounds to MerB occurs at D99 followed, in some cases, by cleavage and loss of the organic moieties and binding of the metal ion product to C96, D99, and C159. The N-terminus of MerA is able to extract the bound PbVI but not the bound SnIV. These results suggest that MerB could be utilized for bioremediation applications, but certain organolead and organotin compounds may present an obstacle by inhibiting the enzyme.

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The Organomercurial LyaseMerB

Cited by 5 publications

References 51 publications

Activation of the Hg–C Bond of Methylmercury by [S₂]-Donor Ligands

Activation of the Hg–C Bond of Methylmercury by [S₂]-Donor Ligands

Structural and Biochemical Characterization of a Copper-Binding Mutant of the Organomercurial Lyase MerB: Insight into the Key Role of the Active Site Aspartic Acid in Hg–Carbon Bond Cleavage and Metal Binding Specificity

Structural and Biochemical Characterization of Organotin and Organolead Compounds Binding to the Organomercurial Lyase MerB Provide New Insights into Its Mechanism of Carbon–Metal Bond Cleavage

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The Organomercurial LyaseMerB

Cited by 5 publications

References 51 publications

Activation of the Hg–C Bond of Methylmercury by [S2]-Donor Ligands

Activation of the Hg–C Bond of Methylmercury by [S2]-Donor Ligands

Structural and Biochemical Characterization of a Copper-Binding Mutant of the Organomercurial Lyase MerB: Insight into the Key Role of the Active Site Aspartic Acid in Hg–Carbon Bond Cleavage and Metal Binding Specificity

Structural and Biochemical Characterization of Organotin and Organolead Compounds Binding to the Organomercurial Lyase MerB Provide New Insights into Its Mechanism of Carbon–Metal Bond Cleavage

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Activation of the Hg–C Bond of Methylmercury by [S₂]-Donor Ligands

Activation of the Hg–C Bond of Methylmercury by [S₂]-Donor Ligands