title: The Mechanochemical Cycle of Mammalian Kinesin-2 KIF3A/B under Load.
abstract: The response of motor proteins to external loads underlies their ability to work in teams and determines the net speed and directionality of cargo transport. The mammalian kinesin-2, KIF3A/B, is a heterotrimeric motor involved in intraflagellar transport and vesicle motility in neurons. Bidirectional cargo transport is known to result from the opposing activities of KIF3A/B and dynein bound to the same cargo, but the load-dependent properties of kinesin-2 are poorly understood. We used a feedback-controlled optical trap to probe the velocity, run length, and unbinding kinetics of mouse KIF3A/B under various loads and nucleotide conditions. The kinesin-2 motor velocity is less sensitive than kinesin-1 to external forces, but its processivity diminishes steeply with load, and the motor was observed occasionally to slip and reattach. Each motor domain was characterized by studying homodimeric constructs, and a global fit to the data resulted in a comprehensive pathway that quantifies the principal force-dependent kinetic transitions. The properties of the KIF3A/B heterodimer are intermediate between the two homodimers, and the distinct load-dependent behavior is attributable to the properties of the motor domains and not to the neck linkers or the coiled-coil stalk. We conclude that the force-dependent movement of KIF3A/B differs significantly from conventional kinesin-1. Against opposing dynein forces, KIF3A/B motors are predicted to rapidly unbind and rebind, resulting in qualitatively different transport behavior from kinesin-1.
authors: Department of Physics, Stanford University, Stanford, CA 94305, USA.
authors: Johan O L
authors: JO
authors: Andreasson
authors: Department of Bioengineering, Pennsylvania State University, University Park, PA 16802, USA.
authors: Shankar
authors: S
authors: Shastry
authors: Department of Bioengineering, Pennsylvania State University, University Park, PA 16802, USA.
authors: William O
authors: WO
authors: Hancock
authors: Department of Biology, Stanford University, Stanford, CA 94305, USA; Department of Applied Physics, Stanford University, Stanford, CA 94305, USA. Electronic address: sblock@stanford.edu.
authors: Steven M
authors: SM
authors: Block
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D016547:Kinesins / Q000502:physiology*; D040542:Mechanotransduction, Cellular; D061987:Sf9 Cells
chemical_list: D016547:Kinesins