Photocleavable Fluorescent Membrane Tension Probes: Fast Release with Spatiotemporal Control in Inner Leaflets of Plasma Membrane, Nuclear Envelope, and Secretory Pathway

Abstract

Mechanosensitive flipper probes are attracting interest as fluorescent reporters of membrane order and tension in biological systems. We introduce PhotoFlippers, which contain a photocleavable linker and an ultralong tether between mechanophore and various targeting motifs. Upon irradiation, the original probe is released and labels the most ordered membrane that is accessible by intermembrane transfer. Spatiotemporal control from photocleavable flippers is essential to access open, dynamic or elusive membrane motifs without chemical or physical interference. For instance, fast release with light is shown to place the original small‐molecule probes into the innermost leaflet of the nuclear envelope to image changes in membrane tension, at specific points in time of membrane trafficking along the secretory pathway, or in the inner leaflet of the plasma membrane to explore membrane asymmetry. These results identify PhotoFlippers as useful chemistry tools to enable research in biology.

The Dynamic Range of Acidity: Tracking Rules for the Unidirectional Penetration of Cellular Compartments

“…Contrary to this tracking of early endosomes with 3 and 4 , the tracking of plasma membrane and mitochondria are solved problems, and practical contributions from 4 are unlikely in this context. Established trackers also exist for the ER, which is not accessible with probes operating by unidirectional penetration [56–58,99] . The same presumably [86–88] also holds for GA tracking with 3 , although the possibility of variable trans selectivity from unidirectional penetration might be worth further attention (Figure 5b) [59] .…”

“…Two complementary approaches exist for specific fluorescence labeling within cells. Cellular engineering with self‐labeling proteins is attractive because it is universal and non‐empirical [98–101] . Empirical tracking appeals because it is simple and user‐friendly, small‐molecule probes can just be added to cells without any engineering [56–58,98–101] .…”

“…Cellular engineering with self-labeling proteins is attractive because it is universal and nonempirical. [98][99][100][101] Empirical tracking appeals because it is simple and user-friendly, small-molecule probes can just be added to cells without any engineering. [56][57][58][98][99][100][101] Because of their empirical nature, the molecular basis of tracking varies broadly.…”

Amphiphilic and Zwitterionic Multi Arylpyrroles with Near‐Infrared Aggregation‐Induced Emission for Cell Membrane Imaging

“…A series of dye cell membranes was developed, including F2 N12S, [6] GGT probe, [9] NR12S based Nile Red, [10] and a series of Photo Flippers. [11] However, there are certain limitations: most dye molecules will reunite in the biological environment and form nanoparticles, which reduces or even quenches the emission of dye molecules, which is called the aggregation-caused quenching (ACQ) effect.…”

“…In situ detection of changes in the cell membrane is crucial, since fluorescent probes that can target the cell membrane can image the cell membrane and track the entire physiological process. A series of dye cell membranes was developed, including F2 N12S, [6] GGT probe, [9] NR12S based Nile Red, [10] and a series of Photo Flippers [11] . However, there are certain limitations: most dye molecules will reunite in the biological environment and form nanoparticles, which reduces or even quenches the emission of dye molecules, which is called the aggregation‐caused quenching (ACQ) effect.…”