A Stable Mercury-Containing Complex of the Organomercurial Lyase MerB: Catalysis, Product Release, and Direct Transfer to MerA
| Autor: | Nathaniel J. Cosper, Gregory Benison, Jacob E. Shokes, Pascale Legault, Robert A. Scott, James G. Omichinski, Paola Di Lello |
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| Rok vydání: | 2004 |
| Předmět: |
Magnetic Resonance Spectroscopy
Time Factors Stereochemistry Lyases Reductase Ligands Biochemistry Catalysis Dithiothreitol Substrate Specificity chemistry.chemical_compound Bacterial Proteins Molecule Organic chemistry Cysteine Ions chemistry.chemical_classification Ligand Spectrophotometry Atomic Mercury Nuclear magnetic resonance spectroscopy Carbon Kinetics Enzyme Models Chemical chemistry Protonolysis Oxidoreductases Protein Binding |
| Zdroj: | Biochemistry. 43:8333-8345 |
| ISSN: | 1520-4995 0006-2960 |
| DOI: | 10.1021/bi049662h |
| Popis: | Bacteria isolated from organic mercury-contaminated sites have developed a system of two enzymes that allows them to efficiently convert both ionic and organic mercury compounds to the less toxic elemental mercury. Both enzymes are encoded on the mer operon and require sulfhydryl-bound substrates. The first enzyme is an organomercurial lyase (MerB), and the second enzyme is a mercuric ion reductase (MerA). MerB catalyzes the protonolysis of the carbon-mercury bond, resulting in the formation of a reduced carbon compound and inorganic ionic mercury. Of several mercury-containing MerB complexes that we attempted to prepare, the most stable was a complex consisting of the organomercurial lyase (MerB), a mercuric ion, and a molecule of the MerB inhibitor dithiothreitol (DTT). Nuclear magnetic resonance (NMR) spectroscopy and extended X-ray absorption fine structure spectroscopy of the MerB/Hg/DTT complex have shown that the ligands to the mercuric ion in the complex consist of both sulfurs from the DTT molecule and one cysteine ligand, C96, from the protein. The stability of the MerB/Hg/DTT complex, even in the presence of a large excess of competing cysteine, has been demonstrated by NMR and dialysis. We used an enzyme buffering test to determine that the MerB/Hg/ DTT complex acts as a substrate for the mercuric reductase MerA. The observed MerA activity is higher than the expected activity assuming free diffusion of the mercuric ion from MerB to MerA. This suggests that the mercuric ion can be transferred between the two enzymes by a direct transfer mechanism. |
| Databáze: | OpenAIRE |
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