Structural Basis for the Selective Pb(II) Recognition of Metalloregulatory Protein PbrR691

The transcription regulator PbrR691, one of the MerR family proteins, shows extremely high sensitivity and selectivity toward Pb­(II) in Ralstonia metallidurans CH34. Here, we present the crystal structure of PbrR691 in complex with Pb­(II) at 2.0 Å resolution. The Pb­(II) coordinates with three conserved cysteines and adopts a unique trigonal-pyramidal (hemidirected) geometry. To our knowledge, the PbrR691-Pb­(II) structure provides the first three-dimensional visualization of a functional hemidirected lead­(II) thiolate coordinate geometry in a protein.