Screening of scFvs against cTnI from Phage Display Antibody Library and Their Expression in E. coli Rosetta

The single chain variable fragments of antibodies(scFvs) against cTnI were screened from the phiage display antibody library by using cTnI as the target antigen. After four rounds of panning, four clones (H2, G5,A9, B9) from the phage display antibody library were verified to show higher binding affinity for cTnI by ELISA and to contain the variable region genes of the light and heavy chains of scFvs by sequencing. The variable region genes of scFvs H2 and G5 were successfully amplified by polymerase chain reactions (PCR) and cloned into expression vector pPELB and expressed as a soluble protein in E. coli Rosetta, whose expression yield was about 2% of total proteins. The expressed proteins were purified by nickel(Ni) affinity chromatography and a single band is shown in the position of 28 kDa on SDS-PAGE. The western blot analysis result verifies that the expressed scFv proteins are capable of binding with monoclonal antibodies against hexa-histidine, indicating that they are hexa-histidin-tagged aim proteins. The immunoassay demonstrates that the expressed scFv proteins are able to specifically react with cTnI molecules. The association constant (KA) values range from 1.2×10^4 to 1.7×10^5 L/mol that are correspondent to the affinities of polyclonal antibodies against cTnI from rabbits. These antibodies can be valuable reagents for the immunoassay of cTnI.