Quantitative screening of yeast surface-displayed polypeptide libraries by magnetic bead capture

Area of Science:

• Biotechnology
• Molecular Biology
• Biophysics

Background:

• High-throughput screening of cell-displayed libraries is crucial for identifying novel binders and improved mutants.
• Flow cytometry is a common method but is limited by equipment cost and availability.
• Cell-displayed libraries offer a powerful platform for protein engineering and drug discovery.

Purpose of the Study:

• To demonstrate magnetic bead capture as a feasible and quantitative method for screening cell-displayed polypeptide libraries.
• To provide an accessible alternative to flow cytometry for laboratories with limited resources.
• To enable the screening of improved mutants and novel binders from cell surface display libraries.

Main Methods:

• Development of a magnetic bead capture assay using streptavidin-coated magnetic beads and biotinylated ligands.
• Correlation of magnetic bead capture probability with surface ligand density on labeled cells.
• Application of the method for enrichment of antibody-displaying cells from a complex library.

Main Results:

• Achieved a single-pass enrichment ratio of 9400-fold for antibody binders from a library with one binder in 1.1 x 10^5 cells.
• Demonstrated quantitative screening capability for both novel binders and improved mutants.
• Obtained significant enrichment ratios for kinetic screening, despite high loss probabilities that can be compensated by oversampling.

Conclusions:

• Magnetic bead capture is a viable and quantitative method for screening cell-displayed libraries.
• This approach lowers the barrier to entry for utilizing cell surface display technology.
• The described methods are analogous to phage display techniques, broadening accessibility for protein engineering.