Multiple kinetic states for the flagellar motor switch

Binding of the Chemotaxis Response Regulator CheY to the Isolated, Intact Switch Complex of the Bacterial Flagellar Motor

“…26). However, it is not known whether this high amplification reflects cooperativity of CheYϳP binding to FliM (4,25,27,28) or amplification of post-binding events at the switch (28). This question cannot be addressed by direct in vitro assays of CheY binding to purified FliM because it is not known whether purified FliM in solution truly represents the native protein within the switch complex and because the inter-FliM interactions, which normally occur within the switch (29), probably do not occur with soluble FliM molecules.…”

The CheZ-binding Surface of CheY Overlaps the CheA- and FliM-binding Surfaces

“…Signals initiated at the receptors are transduced through phosphotransfer reactions that regulate the extent of phosphorylation of CheY (3)(4)(5)(6)(7), the signal molecule of bacterial chemotaxis. Phosphorylated CheY (CheY-P) 1 interacts with the motor switch complex (8 -11) to effect a reversal of flagellar rotation from counterclockwise to clockwise (12)(13)(14). Counterclockwise rotation causes a cell to swim in a straight path, whereas clockwise rotation causes cells to tumble and randomly change their direction of travel.…”

Digital Object Identifier (DOI)

“…Therefore, it will be meaningless to explore the analogy using the pseudo-equilibrium distribution * . Instead, we used the complete perturbative solution of in (26) and found that Segel's analogy does not always hold at O(ξ ). This is attributed to the inherent non-smoothness in the anisotropic tumbling frequency.…”

“…where N t is the total number of chemoreceptors on bacterial surface, a( r, t) describes the time-dependent attractant concentration field in R 3 , K d is the binding constant of the bacterial membrane receptors for chemoattractants, ν is a signal transduction sensitivity factor that scales the input signal (the temporal change in the fractional receptor occupancy) with respect to the output response (the percentage of time spent in flagellar counterclockwise rotation [26,34]), and β 0 is the bacterial basal tumbling frequency in the absence of any chemical gradients. Because the tumbling process for E. coli bacteria bears no long-term memory to the past history [3,5], we assume that the instantaneous β( r, e, t) can be determined by the local chemical gradients at r and t. The dependence of β on r and e indirectly arises from the fact that bacteria sense changes of their surrounding chemoattractants by means of a temporal comparison mechanism [36].…”

“…The coordinated bundle formed by the majority of the flagella rotating in the same (counterclockwise) direction propels the cell to swim smoothly. When the flagellar bundle is disrupted by a reversal in any of the flagellar rotary motors [26,34,42], the swimming motion halts and the cell body twiddles erratically in place, which is called a tumble. The length of the smooth swimming phase varies randomly, and the termination of a smooth swim by a tumble obeys the Poisson process [5,34].…”