The kinesin-13 MCAK has an unconventional ATPase cycle adapted for microtubule depolymerization

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Motors

Background:

• Kinesins are motor proteins that typically move directionally along microtubules.
• The kinesin-13 subfamily, including MCAK, is unique as it depolymerizes microtubules instead of translocating.
• Understanding the functional divergence of structurally similar motor domains is crucial.

Purpose of the Study:

• To elucidate the ATP turnover cycle of the kinesin-13 member, MCAK.
• To understand how MCAK's unique depolymerization function is achieved at the molecular level.
• To compare MCAK's ATP turnover cycle with that of translocating kinesins.

Main Methods:

• Biochemical assays to measure ATP turnover rates.
• Kinetic analysis of ATP hydrolysis and nucleotide exchange.
• Characterization of MCAK's interaction with microtubules and tubulin.

Main Results:

• ATP cleavage, not product release, is the rate-limiting step for MCAK's ATP turnover.
• Unpolymerized tubulin and microtubules accelerate ATP cleavage by MCAK.
• Microtubule ends significantly accelerate ADP-ATP exchange, activating MCAK's ATPase activity.
• MCAK's cycle involves lattice-stimulated cleavage and end-specific exchange, promoting depolymerization.

Conclusions:

• MCAK's altered ATP turnover cycle is adapted for microtubule depolymerization.
• The kinesin motor domain is a versatile nucleotide-dependent engine tunable for transport or depolymerization.
• This study provides mechanistic insight into the functional diversity of kinesin motors.