Phage Display Technology for Food Safety Testing

Phage display technology is a gene expression screening technology, taking to the transformed phage as a carrier to insert the gene fragment to be selected into the phage shell protein area so that foreign peptide or Protein can be expressed and displayed on the phage surface. And then the phage with specific peptide or protein will be panned and expressed, and ultimately the expression of the specific peptide or protein phage, and ultimately the peptide / protein with specific binding properties is developed.

There are 4 methods of phage display technology for food safety testing including random peptide phage display, single-chain F variable region antibody library (scFv) phage display, single domain antibody (sdAbs) and domain antibody (dAbs) phage display. At present, these technologies are mainly used for bacterial pathogens, viruses, mycoplasma, toxins and so on.

1 Bacterial pathogens

Bacterial pathogens detection requires cell surface ligands of clearly infected bacterial. Random peptide phage display can be used to identify the coding genes of bacterial proteins that interact with host proteins. Bacterial genomic DNAs are used to construct phage random peptide libraries(such as the ) artillery phage display peptide library and are inserted into the phage shell protein region. The foreign protein, expressed on the surface of phage, is then screened with the host component to identify the bacterial cell surface ligand gene.

2 Virus

The phage display method was used to detect the viral protein. Firstly, the virus was purified by affinity chromatography and digestion. The phage 12-Mer library was screened by the virus protein molecule. Then the affinity of the phage clone and the viral protein was analyzed by sandwich ELISA method. Next, the positive clones were identified by fiber membrane spot blotting and sequenced to produce a short peptide that interacts with the viral protein, which can be used for rapid detection of such viruses.

3 Mycoplasma

In 2009, a filamentous phage library of a polypeptide was constructed, which is capable of demonstrating the expression of a MmmSC genome fragment to identify the B cell antigen encoding gene of the minor population of Mycoplasma (MmmSC).

4 Parasites

The antigenic epitope can be mapped by screening a library of phage display peptides containing monoclonal antibodies and a TSOL18 mimotope, which provides an alternative approach for the diagnosis and study of Taenia solium vaccines. Taenia solium is a parasite that causes cysticercosis for human, and TSOL18 has been identified as a host to protect the Taenia solium oncosphere antigen.

The monoclonal antibodies to the TSOL18 mouse and the mapped epitopes have a far-reaching effect on the prevention and development of tapeworm infection. In this study, monoclonal antibodies are produced through hybridoma cell technology, taking glycosylated TSOL18, produced by purified Pichia pastoris, as an immunogen.

5 Allergens

At present, different phage libraries can be used to screen the mimotope of linear epitopes and conformational epitopes of allergens, and then the mimotope is transformed into corresponding epitopes by bioinformatics. In 2010, at least 81 different sequences of encoded structures were found by high-throughput screening of the cDNA library of Aspergillus fumigatus allergens. These code structures are able to specific binding to sensitized serum's lgE of Aspergillus fumigatus related complications patients.

6 Toxins

Ochratoxin A (OTA) mimotopes can also be presented by phage technology. The double stranded oligonucleotide with OTA mimic epitopes is cloned to the carrier pC89-COTA. Phage with high-density OTA mimotopes are obtained by optimizing assisting phage MOI, IPTG addition time and dose and other conditions. Next, the optimal expression conditions are tested through ELISA to compare the expressions of different conditions to obtain the high-density OTA mimotopes phage.

Now phage display technology has become a remarkable analysis tool in various fields, such as phage display antibody. In recent years, with the continuous breakthrough of phage display technology, it will embrace a bright prospect in the future.