Zinc-ligand interactions cysteine

The 12 residues between the second cysteine zinc ligand and the first histidine ligand of the classic zinc finger motif form the "finger region". Structurally, this region comprises the second p strand, the N-terminal half of the helix and the two residues that form the turn between the p strand and the helix. This is the region of the polypeptide chain that forms the main interaction area with DNA and these interactions are both sequence specific. 

The two zinc ions fulfill important but different functions in the DNA-binding domains. The first zinc ion is important for DNA-bindlng because it properly positions the recognition helix the last two cysteine zinc ligands are part of this helix. The second zinc ion is important for dimerization since the five-residue loop between the first two cysteine zinc ligands is the main component of the dimer interaction area. 

Excess copper is toxic to cells. On one hand, copper ions can avidly bind to biomolecules by ligand interaction with cysteines or by binding to histidine-rich regions. Copper ions could also be incorporated into proteins instead of zinc or other metal ions during biosynthesis. On the other hand, copper ions can form radicals by a Fenton-type reaction as shown in Eq. (1) ... 

The formation of axially substituted complexes MLL (M = Zn or Cd H2L = porphyrin L = another ligand) has been investigated by a number of groups.1155-1158 An EXAFS study has shown that there is no short axial Zn—S interaction in peptide-substituted zinc porphyrins, in which the side chain bears a cysteine residue.1159 ... 

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