Microtubule C‐Terminal Tails Can Change Characteristics of Motor Force Production

Abstract

Control of intracellular transport is poorly understood, and functional ramifications of tubulin isoform differences between cell types are mostly unexplored. Motors' force production and detachment kinetics are critical for their group function, but how microtubule (MT) details affect these properties -if at all -is unknown. We investigated these questions using both a vesicular transport human kinesin, kinesin-1, and also a mitotic kinesin likely optimized for group function, kinesin-5, moving along either bovine brain or MCF7(breast cancer) MTs. We found that kinesin-1 functioned similarly on the two sets of MTs -in particular, its mean force production was approximately the same, though due to its previously reported decreased processivity, the mean duration of kinesin-1 force production was slightly decreased on MCF7 MTs. In contrast, kinesin-5's function changed dramatically on MCF7 MTs: its average detachment force was reduced and its force-velocity curve was different. In spite of the reduced detachment force, the force-velocity alteration surprisingly improved high-load group function for kinesin-5 on the cancer-cell MTs, potentially contributing to functions such as spindle-mediated chromosome separation. Significant differences were previously reported for C-terminal tubulin tails in MCF7 versus bovine brain tubulin. Consistent with this difference being functionally important, elimination of the tails made transport along the two sets of MTs similar.

Importance of anisotropy in detachment rates for force production and cargo transport by a team of motor proteins

“…In the Stochastic Model, a cargo is driven by a maximum of N motors whose tails are attached to the cargo at a single spot. Motor proteins are modeled as special linkages of stiffness k , such that they exert a restoring force only when they are stretched beyond their rest length l ; and they buckle without any resistance when compressed, similar to kinesin‐1 motors . In Stochastic Model, the amount of load shared by a motor is determined by the relative position of that motor with respect to cargo, and motor stiffness.…”

“…Motor proteins are modeled as special linkages of stiffness k, such that they exert a restoring force only when they are stretched beyond their rest length l; and they buckle without any resistance when compressed, similar to kinesin-1 motors. 5,9,14,15 In Stochastic Model, the amount of load shared by a motor is determined by the relative position of that motor with respect to cargo, and motor stiffness. Thus, an external force F applied to a cargo, which is being driven by n bound/engaged motors out of total N motors available on the cargo, is shared stochastically among n engaged motors.…”

E-hooks provide guidance and a soft landing for the microtubule binding domain of dynein

“…Much of the difference between the various isoforms of both α-tubulin and β-tubulin is due to primary amino acid sequence divergence and posttranslational modifications localized to E-hooks 19 . Cells regulate many processes through E-hook related mechanisms, including microtubule dynamics 26,27 , end binding protein recognition of microtubule plus ends 28 , spastin severing of microtubules 29 , microtubule motor protein motility 30,31 and force production 32 , kinetochore attachment and diffusion along the mitotic spindle 33,34 , tau- microtubule interactions 35 , and multiple other processes.…”

Heterogeneity in kinesin function

“…Kinesin‐family motors play many subcellular roles, and appear adapted to specialized functions with quite different mean velocities and stalling forces, as well as different behavior under load . They serve a wide range of cellular roles, and have a central role in creating and maintaining cellular organization—indeed, impaired function is linked to diseases such as neurodegeneration .…”

“…Kinesin-family motors play many subcellular roles, 1 and appear adapted to specialized functions with quite different mean velocities and stalling forces, as well as different behavior under load. [2][3][4][5] They serve a wide range of cellular roles, and have a central role in creating and maintaining cellular organization-indeed, impaired function is linked to diseases such as neurodegeneration. 6,7 Thus, there is significant interest in achieving a mechanistic understanding of their singlemolecule function, and in relating this to ensemble function involving multiple motors.…”