KIF1D is a fast non-processive kinesin that demonstrates novel K-loop-dependent mechanochemistry

Area of Science:

• Molecular and Cellular Biology
• Biophysics
• Motor Protein Dynamics

Background:

• Kinesin superfamily protein (KSP) KIF1 subfamily members are monomeric motors with unique surface loop insertions.
• A notable insertion, the K-loop, rich in lysine/arginine residues, is present in the L12 loop.
• Conflicting conclusions exist regarding KIF1 motor motility generation, necessitating further investigation.

Purpose of the Study:

• To investigate the functional role of the K-loop in KIF1D, a previously unstudied KIF1 subfamily member.
• To elucidate the mechanism by which KIF1D achieves fast motility despite a slow ATPase rate.
• To resolve discrepancies in understanding KIF1 motor properties.

Main Methods:

• Analysis of KIF1D K-loop using deletion and insertion mutagenesis.
• Characterization of motor properties via steady-state and transient kinetic assays.
• Investigation of microtubule (MT) binding affinity and isomerization dynamics.

Main Results:

• KIF1D was found to be non-chemically processive, exhibiting fast motility with a slow ATPase.
• The K-loop significantly increases KIF1D's affinity for microtubules.
• The K-loop inhibits the transition from weak to strong microtubule binding, coupled with ADP release, stabilizing weak binding and priming the motor for its power stroke.

Conclusions:

• The K-loop is crucial for KIF1D's unique motility mechanism, stabilizing weak microtubule binding.
• This stabilization creates a reservoir of primed motors, facilitating rapid power stroke execution.
• KIF1D's mechanism provides new insights into the diverse strategies employed by KIF1 kinesin motors.