Ligand-Induced Self-Complementing Tag (LiSC-Tag) as an Epitope Tag for Live-Cell Super-Resolution Imaging and Functional Manipulation of Cellular Proteins.

Epitope tags, or peptide tags, are ideal genetically encodable labels for super-resolution imaging due to their compact size. However, their application in live-cell super-resolution imaging of intracellular proteins has been limited by low labeling specificity and efficiency. To address this limitation, we developed the ligand-induced self-complementing tag (LiSC-tag) as a novel epitope tag for live-cell super-resolution imaging and the functional manipulation of cellular proteins. The LiSC-tag utilizes a split FKBP mutant that self-complements upon the addition of small-molecule fluorescent probes. It integrates the compact size of epitope tags with the high brightness and photostability of small-molecule dyes, enabling multicolor nanoscopy imaging using STED, STORM, and SIM. The LiSC-tag exhibits improved brightness and photostability relative to split fluorescent proteins. It is compatible with endogenous protein imaging and can be engineered in tandem arrays to enhance fluorescence signals. Beyond imaging, the LiSC-tag also enables the manipulation of protein localization and targeted protein degradation.