Intact flagellar motor of Borrelia burgdorferi revealed by cryo-electron tomography: evidence for stator ring curvature and rotor/C-ring assembly flexion.
The bacterial flagellar motor is a remarkable nanomachine that provides motility through flagellar rotation. Prior structural studies have revealed the stunning complexity of the purified rotor and C-ring assemblies from flagellar motors. In this study, we used high-throughput cryo-electron tomography and image analysis of intact Borrelia burgdorferi to produce a three-dimensional (3-D) model of the in situ flagellar motor without imposing rotational symmetry. Structural details of B. burgdorferi, including a layer of outer surface proteins, were clearly visible in the resulting 3-D reconstructions. By averaging the 3-D images of approximately 1,280 flagellar motors, a approximately 3.5-nm-resolution model of the stator and rotor structures was obtained. flgI transposon mutants lacked a torus-shaped structure attached to the flagellar rod, establishing the structural location of the spirochetal P ring. Treatment of intact organisms with the nonionic detergent NP-40 resulted in dissolution of the outermost portion of the motor structure and the C ring, providing insight into the in situ arrangement of the stator and rotor structures. Structural elements associated with the stator followed the curvature of the cytoplasmic membrane. The rotor and the C ring also exhibited angular flexion, resulting in a slight narrowing of both structures in the direction perpendicular to the cell axis. These results indicate an inherent flexibility in the rotor-stator interaction. The FliG switching and energizing component likely provides much of the flexibility needed to maintain the interaction between the curved stator and the relatively symmetrical rotor/C-ring assembly during flagellar rotation.
Liu
Jun
J
Department of Pathology and Laboratory Medicine, University of Texas Medical School at Houston, 6431 Fannin, MSB 2.228, Houston, TX 77030, USA. jun.liu.1@uth.tmc.edu
Lin
Tao
T
Botkin
Douglas J
DJ
McCrum
Erin
E
Winkler
Hanspeter
H
Norris
Steven J
SJ
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D025065:Borrelia burgdorferi / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy / Q000379:methods*; D004251:DNA Transposable Elements / Q000235:genetics; D055032:Electron Microscope Tomography / Q000379:methods*; D005407:Flagella / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure*; D016296:Mutagenesis; D009154:Mutation; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000494:pharmacology
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C074899:flgI protein, Bacteria; D011092:Polyethylene Glycols; D017830:Octoxynol; C010615:Nonidet P-40