Structural insights into flagellar stator–rotor interactions

Yunjie Chang,Xiaowei Zhao,MD A Motaleb,Ki Hwan Moon,Steven J Norris,Jun Liu

doi:10.7554/elife.48979

Abstract

The bacterial flagellar motor is a molecular machine that can rotate the flagellar filament at high speed. The rotation is generated by the stator-rotor interaction, coupled with an ion flux through the torque-generating stator. Here we employed cryo-electron tomography to visualize the intact flagellar motor in the Lyme disease spirochete, Borrelia burgdorferi. By analyzing the motor structures of wild-type and stator-deletion mutants, we not only localized the stator complex in situ, but also revealed the stator-rotor interaction at an unprecedented detail. Importantly, the stator-rotor interaction induces a conformational change in the flagella C-ring. Given our observation that a non-motile mutant, in which proton flux is blocked, cannot generate the similar conformational change, we propose that the proton-driven torque is responsible for the conformational change required for flagellar rotation.

Highlights

Many bacterial pathogens require motility to infect, disseminate, and cause disease in humans and other mammalian hosts
MotA/MotB complex in B. burgdorferi is the torque-generating unit powered by proton gradient
Previous studies have shown that wild-type (WT) B. burgdorferi cells were immobilized after being treated with proton uncoupler Carbonyl cyanide 3-chlorophenylhydrazone (CCCP), indicating that the proton gradient is used for flagellar rotation (Motaleb et al, 2000)

Summary

Introduction

Many bacterial pathogens require motility to infect, disseminate, and cause disease in humans and other mammalian hosts. The flagellum is the best understood among bacteria. The flagellum consists of a motor, hook, and long filament (Macnab, 2003; Terashima et al, 2008; Berg, 2003). The motor is a sophisticated nanomachine composed of a rotor, which is the rotary part, and a stator, which surrounds the rotor. The rotation of the motor is driven by the interaction between the rotor and the stator, which is powered by the proton or sodium gradient across the cytoplasmic membrane (Berg, 2003; Sowa and Berry, 2008; Minamino et al, 2008). How the ion gradient couples the mechanical rotation remains elusive at the molecular level

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Results

Conclusion