Fluorescent Membrane Tension Probes for Early Endosomes

Fluorescent flipper probes have been introduced recently to image membrane tension in live cells, and strategies to target these probes to specific membranes are emerging. In this context, early endosomes (EE) targeting without use of protein engineering is especially appealing because it translates into a fascinating transport problem. Weakly basic probes, commonly used to track inside acidic late endosomes and lysosomes, are poorly retained in EE because they are sufficiently neutralized in weakly acidic EE, thus able to diffuse out. Here, we disclose a rational strategy to target EE using a substituted benzylamine with higher pK a as a head group of the flipper probe. The resulting EE flippers are validated for preserved mechanosensitivity, ready for use in biology, particularly to elucidate the mechanics of endocytosis