Mercury is a toxic element with no known biological function and is found in nature at trace levels. Mercury emissions from industrial operations have led to increased levels of this pervasive contaminant in the environment. The highly neurotoxic organomercurial methylmercury is bioaccumulated up trophic levels and can enter the food chain. The biosynthesis of methylmercury is associated with hgcA and hgcB, two genes that are specific to methylating bacteria in anaerobic environments. These genes encode a membrane-associated corrinoid protein, HgcA, and a 2[4Fe-4S] ferredoxin, HgcB, which are hypothesized to be a methyl carrier required for corrinoid cofactor reduction and its associated electron donor, respectively. In the current project, we focus on determining the protein's role in the biomolecular mechanism of mercury methylation. Heterologous expression of the HgcA cobalamin binding domain (CBD) with fusion tags was performed and led to significant improvements in solubility. Reconstitution of HgcA fusion constructs with a cobalamin cofactor in vitro is crucial for structural and functional characterization by NMR, X-ray crystallography and spectroscopic techniques. The results will provide a mechanistic understanding of methylmercury biosynthesis in methylating bacteria.

Expression of HgcA, a protein required for methylmercury biosynthesis

248th National Meeting (2014)

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