Publication Date:
2019-12-10
Description:
Bidirectional vesicle transport along microtubules is necessary for cell viability and function, particularly in neurons. When multiple motors are attached to a vesicle, the distance a vesicle travels before dissociating is determined by the race between detachment of the bound motors and attachment of the unbound motors. Motor detachment rate constants (koff) can be measured via single-molecule experiments, but motor reattachment rate constants (kon) are generally unknown, as they involve diffusion through the bilayer, geometrical considerations of the motor tether length, and the intrinsic microtubule binding rate of the motor. To understand the attachment dynamics of motors bound to fluid lipid bilayers, we quantified the microtubule accumulation rate of fluorescently labeled kinesin-1 motors in a 2-dimensional (2D) system where motors were linked to a supported lipid bilayer. From the first-order accumulation rate at varying motor densities, we extrapolated akoffthat matched single-molecule measurements and measured a 2Dkonfor membrane-bound kinesin-1 motors binding to the microtubule. Thiskonis consistent with kinesin-1 being able to reach roughly 20 tubulin subunits when attaching to a microtubule. By incorporating cholesterol to reduce membrane diffusivity, we demonstrate that thiskonis not limited by the motor diffusion rate, but instead is determined by the intrinsic motor binding rate. For intracellular vesicle trafficking, this 2Dkonpredicts that long-range transport of 100-nm-diameter vesicles requires 35 kinesin-1 motors, suggesting that teamwork between different motor classes and motor clustering may play significant roles in long-range vesicle transport.
Print ISSN:
0027-8424
Electronic ISSN:
1091-6490
Topics:
Biology
,
Medicine
,
Natural Sciences in General
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