Force Induces a Collective Inactivity in Dyneins to Auto-Regulate Bidirectional Transport of Vesicles

Abstract

The back-and-forth (bidirectional) motion of Endosomes and Phagosomes along microtubules is fundamentally important for nutrient absorption, receptor recycling, pathogen degradation and many other downstream cellular pathways. Bidirectional motion requires opposing force from the kinesin and dynein motors, causing intermittent Tug-of-Wars (ToWs) followed by runs where winning motors drive their cargo until the next ToW. Dynein displays a counter-intuitive behaviour of catch bonding tightly to the microtubule against opposing force, but why such a response is needed remains unknown. Here we force dynein to catch-bond using an optical trap when dynein-teams are transporting phagosomes in-vitro and inside cells. An unexpected form of collective inactivity emerges, where larger dynein-teams remain inactive for longer after they have been catch-bonded. Kinesin exhibits a high probability of reversing the cargo during such periods of inactivity of dyneins. Therefore, the inactivity of dyneins allows cells to auto-regulate the effect of opposing molecular forces for the purpose of achieving bidirectional motion of endosomes/phagosomes. We propose that an inactivating conformational change is induced when dynein detaches against strain from its catch-bonded state. Collective inactivity follows because each inactive dynein exerts an entropic force on the other to delay the entire team from being activated. We capture the dynamics of this process through a statistical model of Entropically Constrained Reactivation, obtaining predictions in excellent agreement with experimental data. The emergent behaviour observed here possibly prevents a runaway dynein situation inside cells, its simple entropic origin suggesting broader relevance to catch-bonded receptor ligand interactions operating under conditions of cellular crowding.