Selectivity of Methylation of Metal-Bound Cysteinates and Its Consequences

Abstract

Alkylation of metal-bound cysteinate residues forms an integral step in both the activation of the DNA-damage sensing Ada protein from E. coli and the reaction mechanisms of several zinc-dependent enzymes. The roles of metal ions and the protein structure in regulating the reactivity of bound cysteinate residues is not well-understood. Variants of a consensus zinc finger peptide were used to determine the effects of alkylation of cysteine residues on both metal binding and stability of the peptide structure. The ability of thioethers to act as ligands was probed through the direct synthesis of peptides with methionine or S-methylcysteine replacing the second histidine within the zinc finger framework. This position can be substituted with cysteine with no significant loss of structure or stability. Two-dimensional 1H NMR studies and water exchange experiments of the peptide with S-methylcysteine in this position showed that methylation affected the structure of the peptide−zinc complex in the last turn of...