Kinesin-8/Kip3 requires beta tubulin tail for depolymerase activity

Area of Science:

• Cell Biology
• Molecular Motors
• Cytoskeleton Dynamics

Background:

• Carboxy-terminal tails (CTTs) of tubulin proteins regulate microtubule function.
• Kip3, a kinesin-8 motor, was previously identified as potentially requiring the β-tubulin CTT (β-CTT) for its function.

Purpose of the Study:

• To define how the β-CTT promotes Kip3 function in budding yeast.
• To identify the specific features of the β-CTT important for Kip3's mechanism.

Main Methods:

• Genetic interaction screening in budding yeast.
• In vitro binding and activity assays.
• Microscopy to observe Kip3 localization and microtubule dynamics.

Main Results:

• The β-CTT is necessary for Kip3 depolymerase activity, but not for microtubule binding or motility.
• Yeast cells lacking β-CTT show increased Kip3 accumulation at microtubule plus ends.
• In vitro, β-CTT is required for Kip3 to form a tight complex with soluble tubulin, but not with tubulin in the microtubule lattice.

Conclusions:

• The β-CTT promotes Kip3 depolymerase activity by stabilizing a Kip3-tubulin complex.
• This stabilization is crucial for Kip3 function at microtubule plus ends and in solution.
• The β-CTT acts as a regulatory element for Kip3's microtubule depolymerization activity.