Structural basis of human kinesin-8 function and inhibition.

Area of Science:

• Molecular biology
• Cell biology
• Biochemistry

Background:

• Kinesin motors are crucial for cell division (mitosis) and are targets for cancer drugs.
• Understanding kinesin motor function and inhibition mechanisms is clinically significant.
• Kif18A regulates spindle microtubules via microtubule-based stepping and dynamics regulation.

Purpose of the Study:

• Investigate the mechanism of Kif18A motor function.
• Determine how the small molecule BTB-1 inhibits Kif18A.
• Elucidate the molecular basis of Kif18A inhibition by BTB-1.

Main Methods:

• Biochemical assays to study Kif18A motor activity (microtubule gliding, depolymerization).
• Cryo-electron microscopy (Cryo-EM) to visualize BTB-1-bound Kif18A on microtubules.
• Computational modeling to analyze binding sites and conformational changes.

Main Results:

• Kif18A motor domain drives ATP-dependent microtubule gliding and depolymerizes microtubule ends.
• BTB-1 inhibits both microtubule gliding and depolymerization activities of Kif18A.
• BTB-1 binds to an allosteric site near loop5, blocking ATP-dependent conformational changes and trapping Kif18A on microtubules.

Conclusions:

• BTB-1 inhibits Kif18A by preventing essential conformational changes required for motor function.
• BTB-1's binding site and mechanism differ from other kinesin inhibitors, trapping the motor instead of blocking microtubule binding.
• This study reveals a general mechanism for kinesin inhibition via small molecules targeting the loop5 region.