A cinesina gira de forma unidirecional e gera torque ao caminhar sobre microtúbulos: mero acaso, fortuita necessidade ou design inteligente?

Kinesin rotates unidirectionally and generates torque while walking on microtubules

Avin Ramaiya a,1, Basudev Roy a,1,2, Michael Bugiel a, and Erik Schäffer a,3 

Author Affiliations

a Cellular Nanoscience, Center for Plant Molecular Biology, University of Tübingen, 72076 Tübingen, Germany

Edited by J. Richard McIntosh, University of Colorado, Boulder, CO, and approved August 22, 2017 (received for review April 26, 2017)

Source/Fonte: MakeAGIF

Significance

Given the importance of cytoskeletal motor proteins, we asked whether translational motors rotate while walking along their tracks. Using an optical tweezers-based approach, we simultaneously measured translation, force, rotation, and torque of a kinesin motor with molecular resolution. We found that the gait followed a rotary stepping mechanism that generates torque and spins cargo. Thus, during walking, the motor “tail (and organelle) will tend to wind up like the rubber band of a toy airplane,” as Joe Howard hypothesized in 1996. To determine the overall motor efficiency, our measurements also point to the importance of accounting for rotational work. Apart from other cytoskeletal motors, the technique may be applied to molecular machines such as DNA motors and rotary engines like the ATP synthase.

Abstract

Cytoskeletal motors drive many essential cellular processes. For example, kinesin-1 transports cargo in a step-wise manner along microtubules. To resolve rotations during stepping, we used optical tweezers combined with an optical microprotractor and torsion balance using highly birefringent microspheres to directly and simultaneously measure the translocation, rotation, force, and torque generated by individual kinesin-1 motors. While, at low adenosine 5′-triphosphate (ATP) concentrations, motors did not generate torque, we found that motors translocating along microtubules at saturating ATP concentrations rotated unidirectionally, producing significant torque on the probes. Accounting for the rotational work makes kinesin a highly efficient machine. These results imply that the motor’s gait follows a rotary hand-over-hand mechanism. Our method is generally applicable to study rotational and linear motion of molecular machines, and our findings have implications for kinesin-driven cellular processes.

kinesin optical tweezers polarization microscopy birefringence rotation

Footnotes

1A.R. and B.R. contributed equally to this work.

2Present address: Department of Physics, Indian Institute of Technology, Madras 600036, India.

3To whom correspondence should be addressed. Email: Erik.Schaeffer@uni-tuebingen.de.

Author contributions: E.S. designed research; A.R., B.R., and M.B. performed research; A.R., B.R., M.B., and E.S. analyzed data; and A.R., B.R., and E.S. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1706985114/-/DCSupplemental.

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