Kinetically resolved states of the Halobacterium halobium flagellar motor switch and modulation of the switch by sensory rhodopsin I (original) (raw)
Related papers
Journal of Photochemistry and Photobiology B: Biol., 1994
The swimming behaviour of Halobactetium halobium is influenced by variations in light intensity and wavelength. These stimuli are sensed through two retinal-containing proteins: sensory rhodopsin I and II (SR-I and SR-II), each displaying distinct spectra and photocycles. Light as an energy source is used by H. halobium through two other retinal-containing membrane proteins, acting as photon-driven ionic pumps, bacteriorhodopsin and halorhodopsin. In their ground states, SR-I and SR-II have an absorption maximum at 587 and 487 nm respectively. They have been shown to function as photoreceptors that signal, by a chemical transduction chain, to the motor switch controlling the direction of rotation of a flagellar bundle at the cell pole. Changes from clockwise to counterclockwise rotation or vice versa produce reversals in the swimming direction of H. halobium. Phototaxis occurs because the time interval between reversals is altered by response to light stimuli. SR-I acts as a receptor for attractant (red-orange) light stimuli and displays photochromic properties: when absorption in this wavelength range increases, reversals become less frequent and the pigment is transformed into a blue-absorbing species (SR,&. This intermediate of the SR-I photocycle appears to act both as a signalling state for the reversalsuppressing transduction chain and as a receptor for repellent (blue) light stimuli; these are effective in eliciting more frequent reversals when delivered against a red-orange background. SR-II, also called phoborhodopsin, only senses blue-green light (repellent) stimuli, producing an increased frequency of reversals. This sensor-effecter system has been subjected to various types of analysis and constitutes the second best known example of this kind in prokaryotes, the first being chemotaxis in enterobacteria. Differences and similarities between these two natural models are described. Several mathematical models have been proposed to interpret the mechanisms underlying taxis phenomena. These are typically kinetic schemes for the transduction chain, which are partly hypothetical in H. halobium, due to the limited amount of convincing data on the nature of the (chemical) signal reaching the motor switch. Basically, two types of model have been suggested to account for the time interval distribution of reversals in the swimming behaviour of H. halobium: in the first (of which two variants have been proposed), the stochastic properties of the putative transduction chain signalling to the motor switch are involved; in the second, the hypothesis that an endogeneous oscillator is responsible for the motor switch control is maintained. Structural and biochemical data relevant for a model treatment of the processes occurring at the transduction chain are reported. The available behavioural data in H. halobium are also reported and discussed in detail, comparing the experimental approaches and the different interpretations. The implications of the proposed kinetic models are discussed.
The switching dynamics of the bacterial flagellar motor
Molecular systems …, 2009
Many bacteria are propelled by flagellar motors that stochastically switch between the clockwise and counterclockwise rotation direction. Although the switching dynamics is one of their most important characteristics, the mechanisms that control it are poorly understood. We present a statistical–mechanical model of the bacterial flagellar motor. At its heart is the assumption that the rotor protein complex, which is connected to the flagellum, can exist in two conformational states and that switching between these states depends on the interactions with the stator proteins, which drive the rotor. This couples switching to rotation, making the switch sensitive to torque and speed. Another key element is that after a switch, it takes time for the load to build up, due to conformational transitions of the flagellum. This slow relaxation dynamics of the filament leads, in combination with the load dependence of the switching frequency, to a characteristic switching time, as recently observed. Hence, our model predicts that the switching dynamics is not only controlled by the chemotaxis-signaling network, but also by mechanical feedback of the flagellum.
Journal of bacteriology, 1995
Halobacteria usually respond to repellent light stimuli by reversing their swimming direction. However, cells seem to be in a refractory state when stimulated immediately after performance of a reversal. I found that in this case, a special type of response is exhibited rather than spontaneous behavior. A strong stimulus induced a rhythmic pattern of successive reversals. On stimulation immediately after a reversal of swimming direction, the first of these reversals was skipped without influence on the rhythm. The results suggest that the stimulus evokes an oscillating signal which alters reversal probability but which is itself independent of the state of the motor apparatus. The oscillation has a period length of about 5 s and is damped out within a few cycles. It does not depend on the special sensory photosystem through which the stimulus is applied. The consequences of these findings for the model description of swimming behavior control in halobacteria are discussed.
Coordinated Reversal of Flagellar Motors on a Single Escherichia coli Cell
Biophysical Journal, 2011
An Escherichia coli cell transduces extracellular stimuli sensed by chemoreceptors to the state of an intracellular signal molecule, which regulates the switching of the rotational direction of the flagellar motors from counterclockwise (CCW) to clockwise (CW) and from CW back to CCW. Here, we performed high-speed imaging of flagellar motor rotation and show that the switching of two different motors on a cell is controlled coordinatedly by an intracellular signal protein, phosphorylated CheY (CheY-P). The switching is highly coordinated with a subsecond delay between motors in clear correlation with the distance of each motor from the chemoreceptor patch localized at a cell pole, which would be explained by the diffusive motion of CheY-P molecules in the cell. The coordinated switching becomes disordered by the expression of a constitutively active CheY mutant that mimics the CW-rotation stimulating function. The coordinated switching requires CheZ, which is the phosphatase for CheY-P. Our results suggest that a transient increase and decrease in the concentration of CheY-P caused by a spontaneous burst of its production by the chemoreceptor patch followed by its dephosphorylation by CheZ, which is probably a wavelike propagation in a subsecond timescale, triggers and regulates the coordinated switching of flagellar motors.
A Molecular Mechanism of Bacterial Flagellar Motor Switching
Journal of Molecular Biology, 2009
The high-resolution structures of nearly all the proteins that comprise the bacterial flagellar motor switch complex have been solved; yet a clear picture of the switching mechanism has not emerged. Here, we used NMR to characterize the interaction modes and solution properties of a number of these proteins, including several soluble fragments of the flagellar motor proteins FliM and FliG, and the response-regulator CheY. We find that activated CheY, the switch signal, binds to a previously unidentified region of FliM, adjacent to the FliM-FliM interface. We also find that activated CheY and FliG bind with mutual exclusivity to this site on FliM, because their respective binding surfaces partially overlap. These data support a model of CheY-driven motor switching wherein the binding of activated CheY to FliM displaces the carboxy-terminal domain of FliG (FliG C ) from FliM, modulating the FliG C -MotA interaction, and causing the motor to switch rotational sense as required for chemotaxis.
Bacterial flagellar motor as a multimodal biosensor
Methods, 2020
Bacterial Flagellar Motor is one of nature's rare rotary molecular machines. It enables bacterial swimming and it is the key part of the bacterial chemotactic network, one of the best studied chemical signalling networks in biology, which enables bacteria to direct its movement in accordance with the chemical environment. The network can sense down to nanomolar concentrations of specific chemicals on the time scale of seconds. Motor's rotational speed is linearly proportional to the electrochemical gradients of either proton or sodium driving ions, while its direction is regulated by the chemotactic network. Recently, it has been discovered that motor is also a mechanosensor. Given these properties, we discuss the motor's potential to serve as a multifunctional biosensor and a tool for characterising and studying the external environment, the bacterial physiology itself and single molecular motor biophysics.
Switching of Bacterial Flagellar Motors Is Triggered by Mutant FliG
Biophysical journal, 2015
Binding of the chemotaxis response regulator CheY-P promotes switching between rotational states in flagellar motors of the bacterium Escherichia coli. Here, we induced switching in the absence of CheY-P by introducing copies of a mutant FliG locked in the clockwise (CW) conformation (FliG(CW)). The composition of the mixed FliG ring was estimated via fluorescence imaging, and the probability of CW rotation (CWbias) was determined from the rotation of tethered cells. The results were interpreted in the framework of a 1D Ising model. The data could be fit by assuming that mutant subunits are more stable in the CW conformation than in the counterclockwise conformation. We found that CWbias varies depending on the spatial arrangement of the assembled subunits in the FliG ring. This offers a possible explanation for a previous observation of hysteresis in the switch function in analogous mixed FliM motors-in motors containing identical fractions of mutant FliM(CW) in otherwise wild-type...