Olha o flagelo bacteriano de novo aí na fita, gente!

Dynamics of the bacterial flagellar motor with multiple stators

1. Giovanni Meacci and
2. Yuhai Tu

Edited by Howard C. Berg, Harvard University, Cambridge, MA, and approved January 2, 2009 (received for review October 3, 2008)

Abstract

The bacterial flagellar motor drives the rotation of flagellar filaments and enables many species of bacteria to swim. Torque is generated by interaction of stator units, anchored to the peptidoglycan cell wall, with the rotor. Recent experiments [Yuan J, Berg H.C (2008) Proc Natl Acad Sci USA 105:1182–1185] show that at near-zero load the speed of the motor is independent of the number of stators. Here, we introduce a mathematical model of the motor dynamics that explains this behavior based on a general assumption that the stepping rate of a stator depends on the torque exerted by the stator on the rotor. We find that the motor dynamics can be characterized by two timescales: the moving-time interval for the mechanical rotation of the rotor and the waiting-time interval determined by the chemical transitions of the stators. We show that these two timescales depend differently on the load, and that their cross-over provides the microscopic explanation for the existence of two regimes in the torque-speed curves observed experimentally. We also analyze the speed fluctuation for a single motor by using our model. We show that the motion is smoothed by having more stator units. However, the mechanism for such fluctuation reduction is different depending on the load. We predict that the speed fluctuation is determined by the number of steps per revolution only at low load and is controlled by external noise for high load. Our model can be generalized to study other molecular motor systems with multiple power-generating units.


Keywords: torque-speed - relationship – model – rotary - stepping statistics – speed fluctuation

Footnotes

1 To whom correspondence should be addressed. E-mail: yuhai@us.ibm.com

Author contributions: G.M. and Y.T. designed research, performed research, and wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

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NOTA IMPERTINENTE DO BLOGGER:

Pela insistência do Berg em pesquisar o flagelo bacteriano, ele ainda vai se juntar ao Behe na questão da complexidade irredutível em sistemas biológicos. Meacci e Tu precisam aprender uma regra básica em pesquisas científicas: rever a literatura especializada e mencionar cientistas que têm visões diferentes sobre a questão. Eles não mencionam Behe. Razão? Alguém sabe a razão? Não dar credibilidade científica à tese do Behe.