Enzymes detoxify mercury compounds: bacteria
The enzymatic system of aerobic bacteria detoxifies mercury compounds such as methyl-mercury via the enzymes organomercurial lyase (MerB) and mercuric ion reductase.
|Biomimetic Application Ideas|
|Detoxification of organo-mercury compounds. Emulating enzyme activity independent of genetically modified organisms may be an effective way to decontaminate water, soil, tissue, waste, etc. from methyl-mercury.|
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"Accumulation of extremely toxic methylmercury in the environment—particularly in fish—has triggered an effort by scientists to unravel the process by which a set of bacterial enzymes capture and then detoxify the compound. In a new development, Jonathan G. Melnick and Gerard Parkin of Columbia University report a synthetic mercury complex that provides insight into how one of these enzymes catalyzes cleavage of the Hg-C bond (Science 2007, 317, 225). The finding is expected to boost efforts to genetically modify plants to sequester HgCH3+ for environmental cleanup. In nature, microbes synthesize HgCH3+ from naturally occurring Hg2+, as well as from mercury released in the emissions of coal-fired power plants. Organomercury compounds are toxic because the metal has a high affinity for sulfur, in particular the sulfur of thiol (-SH) groups in cysteine units of proteins. Once the mercury binds, the normal function of the proteins is disrupted. Bacteria resistant to HgCH3+ toxicity produce an enzyme named MerB, which has three cysteine residues in its active site that are known to be crucial for cleaving the Hg-C bond. But the exact way in which MerB coordinates to HgCH3+ and the 'intimate details of the reaction mechanism' have been a mystery, Parkin says. (A second enzyme, MerA, reduces the resulting Hg2+ to less toxic elemental mercury.) Melnick and Parkin thus set out to decipher the mechanism of action of MerB. Melnick and Parkin 'provide an elegant atomic-level description for the facile cleavage of a carbon-mercury bond,' notes James G. Omichinski of the University of Montreal in a Science commentary. Their observations provide valuable insight into the basic mechanism of MerB's activity, he adds. Considerable work remains to be done, but understanding this mechanism 'is essential to efforts to reengineer MerB to improve its catalytic efficiency for the bioremediation of methylmercury,' Omichinski writes." (Ritter 2007:10)
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist
Application Ideas: Detoxification of organo-mercury compounds. Emulating enzyme activity independent of genetically modified organisms may be an effective way to decontaminate water, soil, tissue, waste, etc. from methyl-mercury.
Industrial Sector(s) interested in this strategy: Health, environment, medical, pollution prevention, bioremediation
University of California San Francisco
Gerard Parkin Jonathan G. Melnick
Department of Chemistry, Columbia University