Mapping Protein Binding Sites and Conformational Epitopes Using Cysteine Labeling and Yeast Surface Display

Area of Science:

• Biochemistry
• Molecular Biology
• Immunology

Background:

• Alanine (Ala) scanning is a common technique for identifying protein binding sites, but it often fails to detect residues that are not 'hotspots' despite being in contact with binding partners.
• Many residues involved in protein-ligand interactions are insensitive to Ala substitution, limiting the resolution of traditional scanning mutagenesis.

Purpose of the Study:

• To develop a facile and broadly applicable method for mapping protein:ligand binding sites and conformational epitopes.
• To overcome the limitations of Ala scanning by utilizing Cys scanning mutagenesis and chemical labeling.

Main Methods:

• The study combined Cysteine (Cys) scanning mutagenesis, chemical labeling, and yeast surface display.
• Deep sequencing was employed to analyze the results from yeast surface display.
• The method was applied to map epitopes targeted by antibodies and protein:ligand binding sites.

Main Results:

• Chemical labeling of Cysteine (Cys) residues within a protein binding site consistently abrogated binding, providing a reliable readout.
• The method successfully mapped conformational epitopes and protein:ligand binding sites.
• The technique can distinguish between buried and exposed residues.

Conclusions:

• This Cys scanning mutagenesis and chemical labeling method offers a robust alternative to Ala scanning for mapping protein interaction sites and epitopes.
• The methodology is versatile, does not require purified protein, and can be adapted to various display systems like mammalian cells and viruses.