Bacterial detoxification of Hg(II) and organomercurials.

The most common bacterial mechanism for resistance to mercuric-ion species involves intracellular reduction of Hg(II) to Hg(0). Key proteins of the pathway typically include: MerR, which regulates pathway expression; MerP, which protects the external environment; MerT or MerC, which transport Hg(II) species across the inner membrane; MerA, which catalyses reduction of Hg(II); and sometimes MerB, which catalyses cleavage of C-Hg bonds in organomercurials. Cysteine residues of varying number are arranged in each of the key proteins to optimize their unique roles in sensing (high affinity), transporting (exchangeability), and reducing (redox accessibility) Hg(II). Nature's regulator of this pathway, MerR, is an exquisitely sensitive, Hg(II)-binding, DNA-binding protein that holds the system primed for immediate transcription at the slightest influx of Hg(II).