Chapter 13 - Screening Phage-Displayed Random Peptide Libraries

Abstract

This chapter describes screening phage-displayed random peptide libraries. Screening of phage-displayed random peptide libraries represents a powerful means of identifying peptide ligands for targets of interest. Fundamentally, the screening of phage-displayed random peptide libraries for binding peptides includes the steps such as obtaining a suitable library and source of target, and incubating the library with target and capturing binding phage. It is found that in addition to being used as a vector for accessible expression of peptide libraries, M 13 has been used to display mutant libraries of entire proteins, including antibodies and growth hormone. To minimize problems arising from instability of phage-displayed peptides, phage should be protected from proteolytic degradation. Displayed peptides are susceptible to degradation during phage propagation in a bacterial culture. Elution of phage from the target:phage complex is an important aspect of screening phage-displayed random peptide libraries. One round of affinity purification typically affects the recovery of approximately 1% of PFU representing any given binding clone. The number of phage particles representing any given binding clone that are recovered from the first round is reduced to the point that binding clones may be lost if subjected to a second round of purification without intervening amplification. It is found that enrichment of binding phage may be assessed by doping a library aliquot with an equal number of nonbinding phage which is distinguishable from library phage.