Secondary ligands enhance affinity at a designed metal-binding site.

Area of Science:

• Biochemistry
• Structural Biology
• Protein Engineering

Background:

• Metal ions are crucial for biological processes, with protein-metal interactions dictating function.
• Designing de novo metal-binding sites has focused on metal recruitment, neglecting fine-tuning of the metal environment.

Purpose of the Study:

• To engineer secondary ligands into a designed zinc(II)-binding site.
• To investigate the impact of secondary ligands on metal-binding affinity and site stability.

Main Methods:

• De novo design of a tetrahedral zinc(II)-binding site in a variant of the B1 domain of IgG-binding protein G.
• Introduction of secondary ligands to stabilize histidine residues and fine-tune the metal environment.
• Assessing metal affinity and protein structure changes through mutagenesis and biophysical methods.

Main Results:

• Engineered secondary ligands successfully stabilized metal-coordinating residues and enhanced protein affinity for zinc(II).
• The effects of secondary ligand additions were additive, demonstrating a tunable approach to metal binding.
• Enhanced metal affinity was observed even with a decrease in protein secondary structure.

Conclusions:

• Secondary ligand addition effectively modulates metal-binding affinity and site geometry in designed proteins.
• These findings underscore the significance of secondary interactions for functional metal-binding site design.
• This study represents a foundational step in creating extended, tunable metal-binding environments.