Stochastic switching dynamics of flagellar rotary motors

We study the stochastic direction switching of a flagellar rotary motor as a function of the chemotactic signal CheY-P. We are able to reduce the size of the state space of this Markov process from 4³⁴ to 2 with remarkably good quantitative agreement. Analysis of this model gives an explanation of why the switching shows highly cooperative behavior as a function of CheY-P, while the binding of CheY-P to the motor structure is not cooperative, in agreement with all known data. (paper)