Tetracysteine and Bipartite tags for Biarsenical Organic Fluorophores

Abstract

Genetically encoded fluorescent tags enabling the direct determination of biomolecular functions, interactions and dynamics in living cells and organisms, have had a tremendous impact on cell biology. Key among them are the fluorescent proteins, which despite their great utility present a number of shortcomings. Thus, there has been a very active development of alternative approaches for chemically labeling proteins in live cells, with special interest in small probe molecules. This review depicts a comprehensive review of one of the most remarkable examples of such approaches for intracellular targeting, namely biarsenical ligands that selectively bind to tetracysteine motifs and bipartite dicysteine motifs incorporated into protein targets. The state-of-the-art with respect to small biarsenical molecules and peptide tags are presented, with consideration of their binding properties, labeling aspects, photophysical properties, and applications. The latter include purification of proteins, localization, trafficking and conformational changes of proteins, pulse-chase labeling, chromophore or fluorophore assisted light inactivation (CALI or FALI), correlated fluorescence and electron microscopy (CLEM), and FRET based investigations. The development and applications of bimolecular tetracysteine tags is a recent, promising extension of the method.