Phage display technology was developed by Dr. George P. Smith in 1985 at the University of Missouri. He genetically modified the filamentous phage genome to display foreign peptide sequences on coat protein III (pIII). Phage display technology was further advanced by creating large random phage libraries that can be used in biopanning for affinity selection of high-specificity peptides and antibodies. Today phage display technology continues to be used in drug discovery for the high-throughput selection of polypeptide ligands including peptides, antibodies, antibody fragments, and nanobodies. Two different types of vectors are typically used for the display of peptides and antibodies on one of the coat proteins.
Filamentous Bacteriophage Vectors
The filamentous bacteriophage vectors encode a modified version of the full phage genome. In addition to the wild-type genes, most bacteriophage vectors contain an antibiotic selection gene, as well as a recombinant hybrid gene encoding the foreign peptide or antibody fused to the coat protein. Expression of both the wild type and hybrid genes allows for lower levels of display of the foreign polypeptide. This is often an advantage as low valency often leads to the selection of high-affinity peptide sequences. Bacteriophage vectors are typically not suitable for the display of antibodies and antibody fragments since their large size impairs the infection of E. coli and complicates transformation. However, bacteriophage vectors have been successfully used in peptide phage display. An advantage of bacteriophage vectors is that they do not require the use of helper phage for the propagation of phage particles as the genome contains all of the necessary genes for replication.
Phagemids
Phagemids are plasmid-based vectors that contain both phage and bacterial origins of replication, and an antibiotic selection gene. Additionally, a phagemid vector typically encodes a coat protein (either pIII or pVIII) that is fused to a foreign DNA sequence to be used for the display of full-length antibodies, antibody fragments, nanobodies, or peptides. Since phagemid vectors are plasmid-based, they do not require the presence of helper phage proteins to replicate in E. coli. However, helper phage are essential for the production of phage clones since these contain essential genes that are required to assemble and release phage particles. A major advantage of phagemids is the relatively small size of the vector DNA that enables easy transformation in E. coli. The ability to efficiently transform E. coli is directly related to the resulting diversity of the phage display library and is thus one of the most important considerations to make when choosing an appropriate vector for phage display. In addition, the small size of the phagemid vector makes it easy to manipulate using recombinant DNA technology. Finally, unlike bacteriophage vectors, phagemids can be used to display large proteins such as full-length antibodies and antibody fragments since propagation in E. coli is dependent on a separate helper phage.
Summary
Overall, both bacteriophage vectors and phagemids offer several advantages in phage display technology. Bacteriophage vectors have been successfully used to discover many peptides that target disease-related biomarkers and are easily propagated in E. coli without the use of helper phage. Phagemids have become the most popular vector used in phage display technology due to their ability to express full-length antibodies and antibody fragments as well as other large proteins.
Learn More
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https://www.sciencedirect.com/science/article/abs/pii/S0022283612000927?via%3Dihub
