Kinesin processivity is gated by phosphate release.

Area of Science:

• Molecular motor protein function
• Cellular transport mechanisms
• Biophysics of intracellular transport

Background:

• Kinesin-1 is a crucial dimeric motor protein for intracellular transport, moving along microtubules (MTs) in a hand-over-hand manner.
• It exhibits high processivity, taking over 100 steps before detaching from the MT, but the gating of its two motor heads' mechanochemical cycles remains unclear.

Purpose of the Study:

• To investigate the coordination and gating mechanisms of Kinesin-1's two motor heads during processive movement.
• To elucidate the specific events in the ATP hydrolysis cycle that trigger kinesin dissociation from microtubules.

Main Methods:

• Utilized optical trapping experiments to precisely measure Kinesin-1's step-by-step movement and dissociation dynamics.
• Manipulated the steady-state populations of different ATP hydrolysis states, specifically the posthydrolysis ADP-Pi state, by varying free phosphate concentrations.

Main Results:

• Kinesin-1 dissociation from microtubules occurs concurrently with or after phosphate (Pi) release from ATP hydrolysis.
• Increasing the ADP·Pi state population significantly increased kinesin run length, while altering ATP binding or hydrolysis rates had no effect.
• Tethered-head binding is proposed to occur after hydrolysis, not ATP binding, during processive movement.

Conclusions:

• The structural change driving Kinesin-1 motility, likely neck linker docking, is completed upon ATP hydrolysis, not ATP binding.
• These findings provide critical insights into the gating mechanisms of kinesin motor proteins.
• The results necessitate revisions to current models of the kinesin reaction cycle and its regulation.