MerF is a mercury transport protein: different structures but a common mechanism for mercuric ion transporters?

Mercury resistance determinants are widespread in cram-negative bacteria, b ut vary in the number and identity of genes present, We have shown that the merF gene from plasmid pMER327/419 encodes a 8.7 kDa mercury transport pro tein, by determining in vivo mercury volatilisation when MerF is expressed in the presence of mercuric reductase, Ne have confirmed that MerC of Tn21 is also a mercuric ion transporter. We have been able to detect interaction of the periplasmic protein MerP only with the MerT transporter, and not wi th MerF or MerC. Hydropathy analysis led to the prediction of models for Me rT, MerC and MerF having three, four and two transmembrane regions respecti vely, In all three cases one pair of cysteine residues is predicted to be w ithin the inner membrane with a second pair of cysteine residues on the cyt oplasmic face, and the second helix contains a proline and at least one cha rged residue. The mechanisms of mercuric ion transport may be similar in th ese transporters even though their structures in the membrane differ. (C) 2 000 Federation of European Biochemical Societies.