Halo Tag: Difference between revisions

== Introduction ==

Reversibly photoswitchable fluorescent proteins (RSFPs) are fluorescent proteins whose fluorescence, upon excitation at a certain wavelength, can be switched on or off by light in a reversible manner. <ref> Photoswitchable Fluorescent Proteins: Ten Years of Colorful Chemistry and Exciting Applications https:// doi.org/10.1016/j.cbpa.2013.05.031</ref>. Many current systems are limited in tracking long-term, cyclical processes or in refreshing the pool of observable molecules.

The [Photoswitchable Halo Tag] (psHaloTag) is a unique chemigenetic system designed to provide reversible, light-controlled fluorescence tunable through both genetic and synthetic modifications, with promising applications for dynamic imaging in biological microscopy. psHaloTag addresses a major gap in the availability of reliable, reversible systems suitable for live-cell imaging.  psHaloTag combines the genetically encoded HaloTag protein with the light-sensing sAsLOV2 domain. When illuminated with 450 nm light, psHaloTag undergoes a reversible change that activates a bound rhodamine dye ligand, resulting in a significant increase in fluorescence. This strong, multiple-cycle reporter overcomes the limitations of irreversible systems. It is an important tool for achieving precise spatiotemporal control in demanding applications such as live-cell Super-Resolution Microscopy (SMLM), where many established photosensitive probes cannot be reactivated. <ref> A Photoswitchable HaloTag for Spatiotemporal Control of Fluorescence in Living Cells https://doi.org/10.1002/anie.202424955</ref>