The Power of Three: Dynactin associates with three dyneins under load for greater force production

Cytoplasmic dynein is an essential microtubule motor protein involved in organelle transport and mitotic spindle assembly. Its activity depends on forming dynein-dynactin-cargo adaptor complexes, such as dynein-dynactin-BicD2 (DDB), which typically operate with two dynein motors. We discovered that mechanical tension recruits a third dynein motor via an auxiliary BicD adaptor binding the light intermediate chain of the third dynein. This second BicD molecule stabilizes multi-dynein assemblies, enabling high-force generation. Lis1 further facilitates this adaptation by alleviating dynein autoinhibition. Single-dynein DDB generates ∼2.5 pN of force, increasing to ∼4.5 pN with Lis1, while complexes with two or three motors produce ∼7 pN and ∼9 pN, respectively, consistent with a staggered motor arrangement. Under load, DDB complexes primarily take ∼8 nm steps, challenging current models of dynein coordination. These findings reveal how DDB complexes dynamically sense and adapt to mechanical challenges, ensuring robust intracellular transport under varying force demands.