Steele R A, Opella S J
Department of Chemistry, University of Pennsylvania, Philadelphia 19104, USA.
Biochemistry. 1997 Jun 10;36(23):6885-95. doi: 10.1021/bi9631632.
Bacteria carrying plasmids with the mer operon, which encodes the proteins responsible for the bacterial mercury detoxification system, have the ability to transport Hg(II) across the cell membrane into the cytoplasm where it is reduced to Hg(0). This is significant because metallic mercury is relatively nontoxic and volatile and thus can be passively eliminated. The structures of the reduced and mercury-bound forms of merP, the periplasmic protein, which binds Hg(II) and transfers it to the membrane transport protein merT, have been determined in aqueous solution by multidimensional NMR spectroscopy. The 72-residue merP protein has a betaalpha betabeta alphabeta fold with the two alpha helices overlaying a four-strand antiparallel beta sheet. Structural differences between the reduced and mercury-bound forms of merP are localized to the metal binding loop containing the consensus sequence GMTCXXC. The structure of the mercury-bound form of merP shows that Hg(II) is bicoordinate with the Cys side chain ligands, and this is confirmed by the chemical shift frequency of the 199Hg resonance.
携带含有mer操纵子质粒的细菌，该操纵子编码负责细菌汞解毒系统的蛋白质，这些细菌能够将Hg(II)跨细胞膜转运到细胞质中，在那里它被还原为Hg(0)。这很重要，因为金属汞相对无毒且易挥发，因此可以被动消除。通过多维核磁共振光谱在水溶液中确定了merP（周质蛋白，它结合Hg(II)并将其转移到膜转运蛋白merT）的还原形式和汞结合形式的结构。72个残基的merP蛋白具有β-α-β-β-α-β折叠，两个α螺旋覆盖着一个四链反平行β片层。merP的还原形式和汞结合形式之间的结构差异定位于包含共有序列GMTCXXC的金属结合环。merP的汞结合形式的结构表明，Hg(II)与半胱氨酸侧链配体形成双配位，这通过199Hg共振的化学位移频率得到证实。
