Production of human single-chain antibodies by ribosome display

Characterization of Anti-Citrinin Specific ScFvs Selected from Non-Immunized Mouse Splenocytes by Eukaryotic Ribosome Display

Single chain variable fragments (scFvs) against citrinin (CIT) were selected from a scFv library constructed from the splenocytes of non-immunized mice by an improved eukaryotic ribosome display technology in this study. Bovine serum albumin (BSA)/ CIT-BSA and ovalbumin (OVA)/ CIT-OVA were used as the antigens to select specific anti-CIT scFvs. Eukaryotic in situ RT-PCR method was used to recover the selected mRNA after every affinity selection. After six rounds of ribosome display, expression vector pTIG-TRX carrying specific scFv DNAs were constructed and transformed into Escherichia coli BL21 (DE3) for protein expression. Thirteen positive clones were selected out of which three (designated 23, 68 and 109) showed high binding activity and specificity to CIT by indirect ELISA, while no clone showed binding activity with carrier proteins. The three scFvs showed high specificity to CIT and the cross reactivity with other mycotoxins was below 0.01% as determined by indirect competitive ELISA. These specific scFvs offer a potential novel immunoassay method for CIT residues. This study confirmed the effectiveness of the improved eukaryotic ribosome display system and could be used as a reference for the selection of scFvs specific to other small molecules using ribosome display.

Selection of anti-sulfadimidine specific ScFvs from a hybridoma cell by eukaryotic ribosome display

BACKGROUND

Ribosome display technology has provided an alternative platform technology for the development of novel low-cost antibody based on evaluating antibiotics derived residues in food matrixes.

METHODOLOGY/PRINCIPAL FINDINGS

In our current studies, the single chain variable fragments (scFvs) were selected from hybridoma cell lines against sulfadimidine (SM(2)) by using a ribosome library technology. A DNA library of scFv antibody fragments was constructed for ribosome display, and then mRNA-ribosome-antibody (MRA) complexes were produced by a rabbit reticulocyte lysate system. The synthetic sulfadimidine-ovalbumin (SM(2)-OVA) was used as an antigen to pan MRA complexes and putative scFv-encoding genes were recovered by RT-PCR in situ following each panning. After four rounds of ribosome display, the expression vector pCANTAB5E containing the selected specific scFv DNA was constructed and transformed into Escherichia coli HB2151. Three positive clones (SAS14, SAS68 and SAS71) were screened from 100 clones and had higher antibody activity and specificity to SM(2) by indirect ELISA. The three specific soluble scFvs were identified to be the same molecular weight (approximately 30 kDa) by Western-blotting analysis using anti-E tag antibodies, but they had different amino acids sequence by sequence analysis.

CONCLUSIONS/SIGNIFICANCE

The selection of anti-SM(2) specific scFv by in vitro ribosome display technology will have an important significance for the development of novel immunodetection strategies for residual veterinary drugs.

A pseudoknot improves selection efficiency in ribosome display

The size and diversity of ribosome display libraries depends upon stability of the complex formed between the ribosome, mRNA and translated protein. To investigate if mRNA secondary structure improves stability of the complex, we tested a pseudoknot, originating from the genomic RNA of infectious bronchitis virus (IBV), a member of the positive-stranded coronavirus group. We used the previously-isolated anti-DNA scFv, 3D8, as a target protein. During in vitro translation in rabbit reticulocyte lysate, we observed that incorporation of the pseudoknot into the mRNA resulted in production of a translational intermediate that corresponded to the expected size for ribosomal arrest at the pseudoknot. Complexes containing the mRNA pseudoknot exhibited a higher efficiency of affinity selection than that those without, indicating that the pseudoknot improves stability of the mRNA-ribosome-antibody complex in a eukaryotic translation system. Thus, in order to improve the efficiency of selection, this relatively short pseudoknot sequence could be incorporated into ribosome display.