Phagedisplay

Phage display is a laboratory technique used to study protein interactions by displaying peptides or proteins on the surface of bacteriophages. The displayed polypeptide is genetically fused to a coat protein, creating a physical linkage between the phenotype (the binding peptide) and the genotype (the phage DNA). This enables rapid selection of binding molecules from large libraries.

Typical display systems employ filamentous bacteriophages such as M13. The foreign DNA is fused to a phage coat protein gene, most often pIII or, for high-valency displays, pVIII. The resulting phage particles present the peptide or protein on their surface while carrying the encoding DNA inside the particle. Libraries can be built from random peptide sequences, cDNA fragments, or antibody fragments (such as single-chain variable fragments, scFv, or Fab fragments). Diversity can reach 10^9–10^10 variants in a standard M13 system.

Screening, or biopanning, selects phages that bind a target. Target molecules are immobilized or captured on a surface; phage libraries are exposed, non-binding phages are washed away, and bound phages are eluted and amplified by infection of Escherichia coli. Several rounds enrich high-affinity binders, which are then characterized and sequenced.

Applications include discovery of ligands and epitopes, development of therapeutic antibodies, diagnostic reagents, and vaccine antigens. Advantages include genetic linkage between phenotype and genotype, relatively simple handling, and large library sizes; limitations include potential biases, folding constraints in E. coli, and limited post-translational modification.

History notes: phage display was pioneered by George P. Smith in 1985 and greatly expanded by Greg Winter and colleagues; the technique contributed to Nobel Prize in Chemistry in 2018.