Construction and characterization of M13 bacteriophages displaying gp120 binding domains of human CD4

The envelope glycoprotein, gp120, on the surface of HIV interacts with the human CD4 molecule and thus helps the virus in gaining entry into the T-helper cells. To display the gp120 binding domains of human CD4 on the surface of the bacteriophage M13, two types of vectors have been constructed. In these, the first 176 amino acids of the human CD4 have been fused with the minor coat protein, gIIIp, of M13 bacteriophage for surface display. The Western blot analysis revealed that using the phage based vector, M13CD41923, all the copies of gIIIP (3-5 per virion) were present as fusion protein indicating multivalent display. In the phagemid based vector, phage particles were produced only upon infection of the cells carrying pVCCD43426, with the helper phage, M13KO7. Thus these phage particles carried both, the fusion protein as well as the unfused gIIIp, as shown by Western blot analysis. The presence of large amount of unfused gIIIp ensured that the phage particles did not display more than one fusion protein per phage particle, thus leading to monovalent display. Phage particles produced by both vectors could be captured on immobilized gp120, thereby showing that the displayed CD4 domains were functional.