A Mercury Detoxification Protein Containing Sulfur

Mercury ions are extremely toxic for living cells. They have a high affinity for SH-groups and thus compete with "thiophilic" metals such as zinc, copper and iron in many enzymes.


Some organisms have special mercury binding proteins, which bind the heavy metal ions to organic molecules and thus allow a transport out of the cells. One example is the mercury detoxification protein in the bacterium Shigella flexneri.


  During mercury binding, the cysteine residue changes its position and can no
  longer form hydrogen bonds to the alpha helix.

  Binding the metal causes the whole protein structure to twist, which has a marked
  effect on its surface properties.