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Hg(II) sequestration and protection by the MerR metal-binding domain (MBD)

Jie Qin^1,

Hassan Brim^2,

¹ Department of Microbiology and the Center for Metalloenzyme Studies, University of Georgia, Athens, GA 30602-2605, USA
² Department of Pathology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814-4799, USA

Correspondence
Anne O. Summers
summers{at}uga.edu

MerR, the metalloregulator of the bacterial mercury resistance (mer) operon, binds Hg(II) with high affinity. To study the mechanism of metal-induced activation, a small protein was previously engineered embodying in a single polypeptide the metal-binding domain (MBD) ordinarily formed between two monomers of MerR. Here the physiological and biochemical properties of MBD expressed on the cell surface or in the cytosol were examined, to better understand the environments in which specific metal binding can occur with this small derivative. Over 20 000 surface copies of MBD were expressed per Escherichia coli cell, with metal stoichiometries of 1·0 Hg(II) per MBD monomer. Cells expressing MBD on their surface in rich medium bound 6·1-fold more Hg(II) than those not expressing MBD. Although in nature cells use the entire mer operon to detoxify mercury, it was interesting to note that cells expressing only MBD survived Hg(II) challenge and recovered more quickly than cells without MBD. Cell-surface-expressed MBD bound Hg(II) preferentially even in the presence of a 22-fold molar excess of Zn(II) and when exposed to equimolar Cd(II) in addition. MBD expressed in the cystosol also afforded improved survival from Hg(II) exposure for E. coli and for the completely unrelated bacterium Deinococcus radiodurans.

A supplementary figure showing the construction of the Lpp-OmpA-MBD fusion is available with the online version of this paper.

Present address: Department of Biochemistry and Molecular Biology, Wayne State University School of Medicine, 540 E. Canfield Ave, Detroit, MI 48201, USA.

Present address: Howard University, 2041 Georgia Avenue NW, Washington DC 20060, USA.