InterPro: IPR000815 Mercuric reductase

Proteins that transport heavy metals in micro-organisms and mammals share similarities in their sequences and structures.

A conserved 30-residue domain has been found in a number of these heavy metal transport or detoxification proteins [1]. The domain, which has been termed Heavy-Metal-Associated (HMA), contains two conserved cysteines that are probably involved in metal binding. The HMA domain has been identified in the N-terminal regions of a variety of cation-transporting ATPases (E1-E2 ATPases). In addition, the domain has been found in bacterial mercuric reductase; the copP copper-binding protein of Helicobacter pylori; and in the N-terminal regions of mercuric transport protein periplasmic component (gene merP) and plasmids carried by mercury-resistant Gram-negative bacteria, where it seems to be a mercury scavenger that specifically binds to one Hg⁽²⁺⁾ ion, passing this to mercuric reductase via the merT protein.

The structure of the mercuric ion-binding protein MerP from Shigella flexneri has been determined. The fold has been classed as a ferredoxin-like alpha-beta sandwich, having a beta-alpha beta-beta alpha-beta architecture, with the two alpha-helices overlaying a four-stranded anti-parallel beta- sheet [2]. Structural differences between the reduced and mercury-bound forms of merP are localised to the metal-binding loop containing the consensus sequence GMTCXXC, the two cysteines of which are involved in bi-coordination of Hg(2+) [2].

Mercuric reductase, which contains a single copy of the HMA domain, is involved in a specialised system that confers resistance to Hg⁽²⁺⁾ on catalysing the reaction:

Hg + NADP⁺ + H⁺ = Hg²⁺ + NADPH