The successful screening of a phage-displayed peptide library depends on the nature of the target, the size and information content of the library, as well as the quality of the peptide library.The quality of the peptide library can be reflected by its diversity, which is estimated using statistical methods to assess the conservation or variability of amino acid sequences relative to peptide copy numbers within the peptide population.

I. Display of M13 Phage

By inserting the corresponding nucleotide sequence into a gene encoding a protein, exogenous peptides can be readily fused with the structural proteins of filamentous phage M13. This insertion results in the display of the protein or peptide on the phage surface, provided that the insertion does not interfere with the protein. If the peptide is sufficiently exposed on the phage surface, it can function as a ligand, enzyme, immunogen, or otherwise actively participate in biochemical processes.

The display of peptides and antibody fragments is achieved by coupling them to the minor coat protein pIII of filamentous phage M13, which presents the desired molecules. The pIII protein is located at one end of the phage capsid and consists of three functionally autonomous domains (D1, D2, and D3) connected by glycine-rich linkers. During Gram-negative bacterial infection, the N-terminal D1 domain is responsible for translocating viral DNA into the host cytoplasm. The D2 domain binds to the bacterial F-pilus and plays a central role in the infection process. The C-terminal D3 domain is essential for the assembly of a stable capsid and is a prerequisite for phage production. In most phage display vectors, the pIII protein lacks the D1 and D2 domains, resulting in phage particles with reduced infectivity.

II. Display of T7 Phage

T7 phage is a lytic bacteriophage that replicates within host cells. After amplification, the progeny phages are released through host cell lysis. The displayed peptides do not need to be compatible with the secretory complexes in the bacterial cell membrane or the host cell infection process, thus avoiding the biological constraints associated with the M13 phage display system.

The T7 phage display technology primarily involves two steps: constructing the T7 phage display vector and expressing the target protein.

First, the T7 phage display vector is constructed. This vector typically includes a promoter, a signal peptide sequence, and a DNA sequence linked to the gene of interest. The promoter drives the transcription of the target gene, while the signal peptide sequence facilitates the transfer of the encoded information to the phage’s capsid region, enabling the product of the target gene to bind to the phage’s outer shell.

Next, the target gene is inserted into the T7 phage display vector. This step involves PCR amplification to obtain the target gene’s DNA sequence, followed by directional cloning using restriction enzymes to insert the gene into the vector. The resulting recombinant vector is then transformed into competent E. coli cells. After transformation, the competent bacteria begin expressing the T7 phage display vector and synthesize the target protein. These proteins bind to the phage’s capsid, forming an outward-facing display complex on the exterior of the bacteria. Through appropriate culture conditions and purification steps, a pure display complex can be obtained.

T7 phage display technology has numerous applications. On one hand, it can be used for epitope screening and immunogenicity studies, aiding in the development of new vaccines or diagnostic methods. On the other hand, it can also be applied to enzyme evolution and optimization, enhancing catalytic activity or stability. Additionally, T7 phage display technology is useful for studying receptor-ligand interactions, contributing to drug discovery and the analysis of biomolecular interactions.

III. Similarities and Differences Between M13 Phage and T7 Phage

Phage display technology provides a foundation for the development of fully human therapeutic antibodies and expands the application of directed evolution technology in antibody and peptide engineering and screening, which holds significant importance for the development of antibody drugs.KMD Bioscience has been engaged in antibody research for many years. Our phage display technology services encompass various library types, enabling us to provide clients with monoclonal antibody preparation services derived from multiple species based on our proprietary phage antibody library platform technology. These species include human, mouse, rabbit, chicken, sheep, goose, pig, cow, horse, donkey, camel, alpaca, shark, and more. We offer customized services tailored to clients' needs and provide flexible and efficient screening solutions.