Structure and mechanistic studies of the bacterial organomercurial lyase MerB

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Mercury-containing compounds are introduced into the environment from either natural occurrences or human activity including volcanoes, oceanic emissions, combustion of fossil fuels, dental amalgams, and gold mining. Given the toxicity of mercury-containing compounds, mercury contamination is an extremely important environmental problem, and it is particularly hazardous in aquatic sediments where the highly toxic methylmercury concentrates. Historically, attempts to clean up mercury-contaminated sediments by either physical or chemical remediation have been hampered by the fact that these procedures are expensive and environmentally destructive. As a result, there has been a great deal of focus to develop a bioremediation system to deal with mercury contamination. Such an approach is not only more cost effective but also less disruptive to the natural ecosystems. Mercury-resistant bacteria have developed a system of two enzymes (MerA and MerB) that allows them to efficiently detoxify both ionic and organic mercury compounds by converting them to elemental mercury. Given the unique qualities of these two enzymes, they are ideally for use in bioremediation systems designed for cleaning up mercury-contaminated sediments. For example plants or trees transformed with the genes that produce the MerA and MerB enzymes can grow in the presence of toxic levels of either ionic mercury or methylmercury. When exposed to methylmercury, these transgenic plants and trees extract the MeHg and transpire the less toxic elemental mercury The atmospheric residence time of elemental mercury is about two years, thus it can easily be diluted to trace concentrations before redepositing into terrestrial and deep oceanic sediments. The goal of our project is to better understand the function of MerA and MerB so that they can be better used in bioremediation such as the phytoremediation system for the clean up of methylmercury-contaminated sediments.