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

Proceedings of the National Academy of Sciences of the United States of America 106:28 (2009) 11582-11587

Authors:

T Pilizota, MT Brown, MC Leake, RW Branch, RM Berry, JP Armitage

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 stopstart flagellar motor. Here,weasked,howdoes 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.

The mechanics of slithering locomotion

Proceedings of the National Academy of Sciences of the United States of America Proceedings of the National Academy of Sciences 106:25 (2009) 10081-10085

Authors:

David L Hu, Jasmine Nirody, Terri Scott, Michael J Shelley

Model studies of the dynamics of bacterial flagellar motors.

Biophys J 96:8 (2009) 3154-3167

Authors:

Fan Bai, Chien-Jung Lo, Richard M Berry, Jianhua Xing

Abstract:

The bacterial flagellar motor is a rotary molecular machine that rotates the helical filaments that propel swimming bacteria. Extensive experimental and theoretical studies exist on the structure, assembly, energy input, power generation, and switching mechanism of the motor. In a previous article, we explained the general physics underneath the observed torque-speed curves with a simple two-state Fokker-Planck model. Here, we further analyze that model, showing that 1), the model predicts that the two components of the ion motive force can affect the motor dynamics differently, in agreement with latest experiments; 2), with explicit consideration of the stator spring, the model also explains the lack of dependence of the zero-load speed on stator number in the proton motor, as recently observed; and 3), the model reproduces the stepping behavior of the motor even with the existence of the stator springs and predicts the dwell-time distribution. The predicted stepping behavior of motors with two stators is discussed, and we suggest future experimental procedures for verification.

Direct Observation Of Rotation Of F1-Atpase From Saccharomyces cerevisiae With mgi Mutations

Biophysical Journal Elsevier 96:3 (2009) 143a-144a

Authors:

Bradley C Steel, Yamin Wang, Vijay Pagadala, Richard M Berry, David M Mueller

Experimental Evidence for Conformational Spread in the Bacterial Switch Complex

Biophysical Journal Elsevier 96:3 (2009) 630a

Authors:

Richard W Branch, Fan Bai, Dan V Nicolau, Teuta Pilizota, Bradley Steel, Philip K Maini, Richard M Berry