Supramolecular latching system based on ultrastable synthetic binding pairs as versatile tools for protein imaging

Here we report ultrastable synthetic binding pairs between cucurbit[7]uril (CB[7]) and adamantyl- (AdA) or ferrocenyl-ammonium (FcA) as a supramolecular latching system for protein imaging, overcoming the limitations of protein-based binding pairs. Cyanine 3-conjugated CB[7] (Cy3-CB[7]) can visualize AdA- or FcA-labeled proteins to provide clear fluorescence images for accurate and precise analysis of proteins. Furthermore, controllability of the system is demonstrated by treating with a stronger competitor guest. At low temperature, this allows us to selectively detach Cy3-CB[7] from guest-labeled proteins on the cell surface, while leaving Cy3-CB[7] latched to the cytosolic proteins for spatially conditional visualization of target proteins. This work represents a non-protein-based bioimaging tool which has inherent advantages over the widely used protein-based techniques, thereby demonstrating the great potential of this synthetic system.
Although protein-ligand pairs are useful tools for bioimaging, they are susceptible to enzymatic degradation and interference from endogenous species. Here, the authors show that a synthetic and bioorthogonal cucurbit[7]uril-guest binding pair can be used to visualize proteins in cells, overcoming limitations of protein-based platforms.