Flagelo bacteriano usa 'freio molecular': acaso, necessidade ou design inteligente?

A molecular brake, not a clutch, stops the Rhodobacter sphaeroides flagellar motor

Teuta Pilizotaa,1,2, Mostyn T. Brownb,1, Mark C. Leakea,c, Richard W. Brancha, Richard M. Berrya and Judith P. Armitageb,c,3

+Author Affiliations

aThe Clarendon Laboratory, Department of Physics, Oxford University, Parks Road, Oxford OX1 3PU, United Kingdom;

bDepartment of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom; and

cOxford Centre for Integrative Systems Biology (OCISB), Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom

↵1T.P. and M.T.B contributed equally to this work.

Edited by George F. Oster, University of California, Berkeley, CA, and approved May 29, 2009 (received for review December 28, 2008)

Abstract

Many bacterial species swim by employing ion-driven molecular motors that power the rotation of helical filaments. Signals are transmitted to the motor from the external environment via the chemotaxis pathway. In bidirectional motors, the binding of phosphorylated CheY (CheY-P) to the motor is presumed to instigate conformational changes that result in a different rotor-stator interface, resulting in rotation in the alternative direction. Controlling when this switch occurs enables bacteria to accumulate in areas favorable for their survival. Unlike most species that swim with bidirectional motors, Rhodobacter sphaeroides employs a single stop-start flagellar motor. Here, we asked, how does the binding of CheY-P stop the motor in R. sphaeroides—using a clutch or a brake? By applying external force with viscous flow or optical tweezers, we show that the R. sphaeroides motor is stopped using a brake. The motor stops at 27–28 discrete angles, locked in place by a relatively high torque, approximately 2–3 times its stall torque.

Footnotes

3To whom correspondence should be addressed. E-mail: judith.armitage@bioch.ox.ac.uk

Author contributions: T.P., M.T.B., R.M.B., and J.P.A. designed research; T.P. and M.T.B. performed research; M.C.L. contributed new reagents/analytic tools; T.P., M.T.B., and R.W.B. analyzed data; and T.P. and M.T.B. wrote the paper.

↵2Present address: Carl Icahn Laboratory, Princeton University, Washington Road, Princeton, NJ 08544.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

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