Por que a kinesina é tão processiva: mero acaso, necessidade ou design inteligente???

Why kinesin is so processive

Erdal Topraka,b,1, Ahmet Yildizc, Melinda Tonks Hoffmanb, Steven S. Rosenfeldd,2 and Paul R. Selvina,b,2

+Author Affiliations

aCenter for Biophysics and Computational Biology, and

bDepartment of Physics, University of Illinois at Urbana–Champaign, Urbana, IL 61801;

cDepartment of Physics, University of California, Berkeley, CA 94720; and

dDepartments of Neurology and Cell Biology and Pathology, Columbia University, New York, NY 10032

Edited by Edwin W. Taylor, Northwestern University Feinberg School of Medicine, Chicago, IL, and approved June 16, 2009 (received for review August 27, 2008)

Abstract

Kinesin I can walk on a microtubule for distances as long as several micrometers. However, it is still unclear how this molecular motor can remain attached to the microtubule through the hundreds of mechanochemical cycles necessary to achieve this remarkable degree of processivity. We have addressed this issue by applying ensemble and single-molecule fluorescence methods to study the process of kinesin stepping, and our results lead to 4 conclusions. First, under physiologic conditions, ≈75% of processively moving kinesin molecules are attached to the microtubule via both heads, and in this conformation, they are resistant to dissociation. Second, the remaining 25% of kinesin molecules, which are in an “ATP waiting state” and are strongly attached to the microtubule via only one head, are intermittently in a conformation that cannot bind ATP and therefore are resistant to nucleotide-induced dissociation. Third, the forward step in the kinesin ATPase cycle is very fast, accounting for <5% of the total cycle time, which ensures that the lifetime of this ATP waiting state is relatively short. Finally, by combining nanometer-level single-molecule fluorescence localization with higher ATP concentrations than used previously, we have determined that in this ATP waiting state, the ADP-containing head of kinesin is located 8 nm behind the attached head, in a location where it can interact with the microtubule lattice. These 4 features reduce the likelihood that a kinesin I motor will dissociate and contribute to making this motor so highly processive.

fluorescence motility gating fluorescence imaging with 1-nm accuracy processivity
Footnotes

2To whom correspondence may be addressed. E-mail: sr2327@columbia.edu or selvin@uiuc.edu

Author contributions: S.S.R. and P.R.S. designed research; E.T. and M.T.H. performed research; A.Y. contributed new reagents/analytic tools; E.T., S.S.R., and P.R.S. analyzed data; and E.T., S.S.R., and P.R.S. wrote the paper.

↵1Present address: Department of Systems Biology, Harvard Medical School, Boston, MA 02115.

The authors declare no conflict of interest.

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This article is a PNAS Direct Submission.