Insights from engineering the Affibody-Fc interaction with a computational-experimental method

Area of Science:

• Protein Engineering
• Computational Biology
• Immunology

Background:

• The interaction between Staphylococcal Protein A (SpA) domain B and IgG Fc is fundamental for Affibody applications in affinity chromatography and inflammatory disease therapies.
• Despite its significance, this SpA-Fc interaction has not undergone affinity maturation.
• Understanding this interaction is crucial for developing advanced Affibody-based biotechnologies.

Purpose of the Study:

• To computationally elucidate reasons for the rarity of single-substitution affinity improvements in SpA for Fc binding.
• To identify specific SpA substitutions with potential engineering applications and modulated binding affinities.
• To explore the utility of computational methods for protein-protein interaction analysis.

Main Methods:

• Utilized a modified FoldX algorithm to predict changes in protein-protein binding affinity.
• Generated a list of 41 single-amino acid substitutions in the SpA molecule.
• Analyzed substitutions for their impact on affinity, charge, and other properties.

Main Results:

• Identified nine single-amino acid substitutions in SpA affecting Fc binding affinity.
• Four substitutions showed near wild-type affinity, while five exhibited up to a four-fold change.
• Discovered substitutions that alter charge and remove specific residues like lysine.

Conclusions:

• Subtle affinity modulations through SpA substitutions can be valuable for optimizing chromatographic elution conditions.
• The computational approach provides molecular insights with reduced experimental effort compared to traditional methods.
• This methodology is transferable to the affinity maturation of other protein-protein interaction systems.