Site-Specific Antibody Fragment Conjugates for Reversible Staining in Fluorescence Microscopy.

Antibody conjugates have taken a great leap forward as tools in basic and applied molecular life sciences, which was enabled by the development of chemoselective reactions for the site-specific modification of proteins. Antibody-oligonucleotide conjugates combine the antibody's target specificity with the reversible, sequence-encoded binding properties of oligonucleotides like DNAs or PNAs, allowing sequential imaging of large numbers of targets in a single specimen. In this report, we use the Tub-tag Ⓡ technology in combination with Cu-catalyzed azide-alkyne-cycloaddition for the site-specific conjugation of single DNA and PNA strands to an eGFP-binding nanobody. We show binding of the conjugate to recombinant eGFP and subsequent sequence-specific annealing of fluorescently labelled imager strands. Furthermore, we reversibly stain eGFP-tagged proteins in human cells, thus demonstrating the suitability of our conjugation strategy to generate antibody-oligonucleotides for reversible immunofluorescence imaging.