Preparation of a bio-immunoreagent between ZZ affibody and enhanced green fluorescent protein for immunofluorescence applications

Development of a mammalian cell-based ZZ display system for IgG quantification

BACKGROUND

Biological laboratories and companies involved in antibody development need convenient and versatile methods to detect highly active antibodies.

METHODS

To develop a mammalian cell-based ZZ display system for antibody quantification, the eukaryotic ZZ-displayed plasmid was constructed and transfected into CHO cells. After screening by flow cytometric sorting, the stable ZZ display cells were incubated with reference IgG and samples with unknown IgG content for 40 min at 4℃, the relative fluorescence intensity of cells was analyzed and the concentration of IgG was calculated.

RESULTS

By investigating the effects of different display-associated genetic elements, a eukaryotic ZZ-displaying plasmid with the highest display efficiency were constructed. After transfection and screening, almost 100% of the cells were able to display the ZZ peptide (designated CHO-ZZ cells). These stable CHO-ZZ cells were able to capture a variety of IgG, including human, rabbit, donkey and even mouse and goat. CHO-ZZ cells could be used to quantify human IgG in the range of approximately 12.5-1000 ng/mL, and to identify high-yielding engineered monoclonal cell lines.

CONCLUSIONS

We have established a highly efficient CHO-ZZ display system in this study, which enables the quantification of IgG from various species under physiological conditions. This system offers the advantage of eliminating the need for antibody purification and will contribute to antibody development.

Fc-specific and covalent conjugation of a fluorescent protein to a native antibody through a photoconjugation strategy for fabrication of a novel photostable fluorescent antibody

Fluorophore-antibody conjugates with high photobleaching resistance, high chemical stability, and Fc-specific attachment is a great advantage for immunofluorescence imaging. Here, an Fc-binding protein (Z-domain) carrying a photo-cross-linker (p-benzoylphenylalanine, Bpa) fused with enhanced green fluorescent protein (EGFP), namely photoactivatable Z_Bpa-EGFP recombinant, was directly generated using the aminoacyl-tRNA synthetase/suppressor tRNA technique without any further modification. By employing the photoactivatable Z_Bpa-EGFP, an optimal approach was successfully developed which enabled EGFP to site-selectively and covalently attach to native antibody (IgG) with approximately 90% conjugation efficiency. After characterizing the Fc-specific and covalent manner of the EGFP-photoconjugated antibody, its excellent photobleaching resistance for immunofluorescence imaging was demonstrated in a model study by monitoring the toll-like receptor 4 (TLR4) expression in HepG2 cells. The proposed approach here for the preparation of a novel fluorescent antibody is available and reliable, which would play an important role in fluorescence immunoassay, and is expected to be extended to the generation of other biomolecule-photoconjugated antibodies, such as other fluorescent proteins for multiplex immunofluorescence imaging or reporter enzymes for highly sensitive enzyme immunoassays.Graphical abstract.