The lever arm created by the stiff stalk of NDC80 tilted toward the plus-end of the microtubule is critical for its asymmetric unbinding under directional mechanical loads, highlighting design principles of microtubule-associated proteins.
Many microtubule-associated proteins (MAPs) function under mechanical loads. Among them, motor proteins and passive couplers link microtubules with other cytoskeletal filaments, membranous structures and diverse scaffolds to enable cell shape changes, locomotion and other important processes. A key kinetochore complex, NDC80, transmits forces from microtubule disassembly to chromosome motion during cell division. Recently, this complex has been shown to detach from microtubules more easily when pulled toward the minus-end of the microtubule than when pulled in the plus-end direction. Here, we used coarse-grained molecular dynamics and Brownian dynamics simulations to explain the asymmetric effect of the directional load on the unbinding of the NDC80 complex from microtubules and then generalized our findings to other MAPs. We found that the lever arm created by the stiff stalk of NDC80 tilted toward the plus-end of the microtubule is critical for asymmetric unbinding of this complex, similar to that of dynein. In contrast, EB-proteins, the microtubule crosslinker PRC1, and kinesins are predicted to lack pronounced unbinding asymmetry, either due to their almost perpendicular anchorage to the microtubule wall or due to the high flexibility of their linker regions proximal to the microtubule-binding domains. Thus, our study highlights some of the design principles of MAPs, explaining how their distal parts can impart, modulate or eliminate the dependence of unbinding on the direction of external loads. This information deepens our understanding of the load-bearing properties and functions of diverse MAPs and may guide the design of synthetic protein systems with predefined mechanical characteristics.
Kovalenko et al. (2025) studied this question.