Biomimetic behaviour in artificially created active matter that allows deterministic and controlled motility has become of growing interest in recent years. It is well known that phototrophic ...bacteria optimize their position with respect to light by phototaxis. Here, we describe how our fully artificial, magnetic and photocatalytic microswimmers undergo a specific type of behaviour that strongly resembles phototaxis: when crossing an illuminated stripe the particles repeatedly turn back towards the light once they reach the dark region, without any obvious reason for the particles to do so. In order to understand the origin of this behaviour we analyze different influences and elucidate through experiments and theoretical considerations that this behavior arises from a combination of orientational stabilization through activity and destabilizing Brownian motion. This interplay shows beautifully how simple physical effects can combine into complex behaviours.
To improve the understanding of phototaxis, we investigate the origin of our photocatalytic particles' peculiar scotophobicity (fear of darkness).
Microtubule motors play key roles in cellular functions, such as transport, mitosis and cell motility. Fueled by ATP hydrolysis, they convert chemical energy into mechanical work, which enables their ...movement on microtubules. While their motion along the long axis of microtubules has been studied extensively, some motors display an off-axis component, which results in helical motion around microtubules and the generation of torque in addition to linear forces. Understanding these nuanced movements expands our comprehension of motor protein dynamics and their impact on cellular processes.
During mitosis, motor proteins and microtubule-associated protein organize the spindle apparatus by cross-linking and sliding microtubules. Kinesin-5 plays a vital role in spindle formation and ...maintenance, potentially inducing twist in the spindle fibers. The off-axis power stroke of kinesin-5 could generate this twist, but its implications in microtubule organization remain unclear. Here, we investigate 3D microtubule-microtubule sliding mediated by the human kinesin-5, KIF11, and found that the motor caused right-handed helical motion of anti-parallel microtubules around each other. The sidestepping ratio increased with reduced ATP concentration, indicating that forward and sideways stepping of the motor are not strictly coupled. Further, the microtubule-microtubule distance (motor extension) during sliding decreased with increasing sliding velocity. Intriguingly, parallel microtubules cross-linked by KIF11 orbited without forward motion, with nearly full motor extension. Altering the length of the neck linker increased the forward velocity and pitch of microtubules in anti-parallel overlaps. Taken together, we suggest that helical motion and orbiting of microtubules, driven by KIF11, contributes to flexible and context-dependent filament organization, as well as torque regulation within the mitotic spindle.
Synopsis
Kinesin motors are involved in organizing the mitotic spindle by cross-linking and sliding microtubules. This work shows that the sideways stepping of human kinesin-5, KIF11, causes helical motion of anti-parallel microtubules and orbiting motion of parallel microtubules.
KIF11 drives a right-handed helical motion of short microtubules around long, suspended microtubules in anti-parallel overlaps.
The microtubule-microtubule distance (i.e., motor extension) decreases with increasing sliding velocity.
KIF11 drives an orbiting motion of parallel microtubules at nearly full motor extension.
Altering the length of the KIF11 neck linker increases forward velocity and pitch of microtubules in anti-parallel overlaps.
Sideways stepping of human KIF11 causes helical and orbiting motions of microtubules that may contribute to flexible filament formation and mitotic spindle torque regulation.
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