Protein engineering by cell-surface display.

Protein libraries displayed on cell surfaces can be labeled with soluble ligands exhibiting well-characterized binding equilibria and dissociation kinetics, and then quantitatively screened by flow cytometry at a rate of >10(4) clones/second. The promise of cell-surface display for directed evolution is being realized, with significant improvements recently reported in protein ligand binding affinity, stability, expression and enzymatic activity.