Ligand Field Stabilization Control of Metal Ion Binding.

摘要

Specific metal ions bind to particular sites within proteins. The factors that might influence the thermodynamics of metal ion binding to proteins include metal ion radius, hard-soft acid-base effects, and ligand field stabilization energy changes. We have probed the contributions of these effects through the use of a series of peptides based on naturally occuring 'zinc finger' domains. The metal ion binding sites studied include Cys2His2, Cys3His, Cys4, and Cys2His(X) where X = OH2, Cl(-), N(-) methylimidazole, and (-)SCH2CH2OH. Metal ions tested included Zn(II), Co(II), Cd(II), Fe(II), Ni(II), and Mn(II). We found that ligand field stabilization energy changes quantitatively account for preferences for Zn(II) over Co(II). For Cd(II), hard-soft acid-base effects are dominant with a greater than 100-fold increase in affinity for Cd(II) over Zn(II) for each Cys for 'His' replacement. For other metal ions, multiple factors clearly contribute. These studies provide components for a rational basis for the design of specific metal binding sites for biosensors and other applications.