Live cell PNA labelling enables erasable fluorescence imaging of membrane proteins

DNA nanotechnology is an emerging field, which promises fascinating opportunities for the manipulation and imaging of proteins on a cell surface. The key to progress in the area is the ability to create the nucleic acid-protein junction in the context of living cells. Here we report a covalent labelling reaction, which installs a biostable peptide nucleic acid (PNA) tag. The reaction proceeds within minutes and is specific for proteins carrying a 2 kDa coiled coil peptide tag. Once installed the PNA label serves as a generic landing platform that enables the recruitment of fluorescent dyes via nucleic acid hybridization. We demonstrate the versatility of this approach by recruiting different fluorophores, assembling multiple fluorophores for increased brightness, and achieving reversible labelling by way of toehold mediated strand displacement. Additionally, we show that labelling can be carried out using two different coiled coil systems, with EGFR and ETBR, on both HEK293 and CHO cells. Finally, we apply the method to monitor internalization of EGFR on CHO cells.