Detection of sub-8-nm movements of kinesin by high-resolution optical-trap microscopy.
Kinesin is a molecular motor that transports organelles along microtubules. This enzyme has two identical 7-nm-long motor domains, which it uses to move between consecutive tubulin binding sites spaced 8 nm apart along a microtubular protofilament. The molecular mechanism of this movement, which remains to be elucidated, may be common to all families of motor proteins. In this study, a high-resolution optical-trap microscope was used to measure directly the magnitude of abrupt displacements produced by a single kinesin molecule transporting a microscopic bead. The distribution of magnitudes reveals that kinesin not only undergoes discrete 8-nm movements, in agreement with previous work [Svoboda, K., Schmidt, C. F., Schnapp, B. J. & Block, S.M. (1993) Nature (London) 365, 721-727], but also frequently exhibits smaller movements of about 5 nm. A possible explanation for these unexpected smaller movements is that kinesin's movement from one dimer to the next along a protofilament involves at least two distinct events in the mechanical cycle.
Coppin
C M
CM
Department of Pharmacology and Howard Hughes Medical Institute, University of California, San Francisco, 94143, USA.
Finer
J T
JT
Spudich
J A
JA
Vale
R D
RD
D000818:Animals; D002474:Cell-Free System; D016547:Kinesins / Q000502:physiology*; D008297:Male; D008853:Microscopy / Q000295:instrumentation; D008870:Microtubules / Q000502:physiology*; D009068:Movement; D012617:Sea Urchins; D013082:Sperm Tail / Q000648:ultrastructure
D016547:Kinesins