Kinesin-4 KIF21B is a potent microtubule pausing factor

Area of Science:

• Cell Biology
• Molecular Motors
• Cytoskeleton Dynamics

Background:

• Microtubules are essential cytoskeletal polymers exhibiting dynamic growth, shrinkage, and pausing.
• Factors regulating microtubule pausing remain largely unidentified, hindering understanding of cytoskeletal dynamics.

Purpose of the Study:

• To investigate the role of mammalian kinesin-4 KIF21B in regulating microtubule dynamics.
• To elucidate the molecular mechanisms by which KIF21B influences microtubule plus-end behavior.

Main Methods:

• In vitro reconstitution assays to observe microtubule growth and pausing.
• Biochemical analyses to identify functional domains of KIF21B.
• Microscopy to visualize KIF21B interaction with microtubule plus ends.

Main Results:

• KIF21B is a processive motor that accumulates at microtubule plus ends, inducing significant growth inhibition.
• Microtubule pausing activity is mediated by non-motor domains, including the stalk and WD40 domains.
• KIF21B's tail prefers GTP- over GDP-microtubules, facilitating plus-end association.
• A motor-inhibiting domain enhances pausing by preventing KIF21B detachment.

Conclusions:

• KIF21B acts as an autonomous microtubule pausing factor.
• The protein integrates microtubule-binding and regulatory functions to control microtubule dynamics.
• KIF21B offers novel insights into the regulation of cytoskeletal stability.