Graduate Thesis Or Dissertation
 

Kinesin-14 Motors with Novel Motility Behaviors and Functions

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  • Cell division, arguably the most important event during the life cycle of the eukaryotic cell, is achieved through a complicated yet beautiful machinery. The mitotic spindle — a microtubule-based bipolar structure—is the cellular machinery responsible for the correct segregation of the genetic material, chromosomes. The protein-based nanomachines termed molecular motors play important roles in most activities, including maintaining the correct orientation of the mitotic spindle and generating force to separate the replicated chromosomes. The molecular motor is a general term for proteins that can convert chemical energy into mechanical energy. One class of molecular motor, known as kinesin, is essential for many processes within the mitotic spindle. The kinesin superfamily includes 14 different subfamilies based on their structure and functions. Kinesins use microtubules as tracks and move on them. Despite extensive study, many aspects of kinesin functions and regulations are still not fully understood. In this dissertation, one of the kinesin family, kinesin-14, is investigated and discussed. Using the technologies including high precision tracking, single molecular imaging and biochemistry assays, these investigations reported two kinesin-14 motors with novel motility behaviors and their interactions with microtubules. In Chapter three, a kinesin-14, AnKIN14, from Aspergillus niger is characterized. Unlike most of the kinesin-14s that have been studied, AnKIN14 is plus-end-directed and processive on a single microtubule as a single motor. AnKIN14 is also found to be a context-dependent bidirectional motor that uses its tail to regulate its motility. These results strengthened the notion that bidirectionality is a unique property of mitotic kinesins. In Chapter four, a kinesin-14 from Giardia intestinalis, GiKIN14a, is investigated. GiKIN14a is the first Ncd-like kinesin-14 that intrinsically has the highly processive minus-end-directed motility. In the investigation, GiKIN14a is found to achieve this long-range motility by utilizing its microtubule-binding tail and the flexible hinge in its central stalk. Further study shows the tail domain enhances GiKIN14a stepping rate and ATP hydrolysis. This finding greatly deepened our understanding of the kinesin structural effects on its motility and enriched our current mechanistic understanding of kinesin-14 processivity. In Chapter five, the research is focused on the regulatory effects of kinesin-14s on the microtubules. A novel microtubule regulator derived from a kinesin-14 motor can reverse the dynamic polarity of microtubules. With the enhanced minus-end-directed motility, the kinesin- 14 mutant can suppress the microtubule growth at the plus end while enhancing the microtubule growth at the minus end, opposite to the dynamic instability of microtubules and unlike any other regulators that have been studied to date. This finding shows the vast potential of modified kinesin motors as regulators of the microtubules. It also can help us have a better understanding of the mechanism of motor-based microtubule regulation.
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