POSTERS - BLAST X - University of Utah

BLAST X Poster #37
MOLECULAR ARCHITECTURE OF INTACT FLAGELLAR MOTOR REVEALED BY CRYO-
ELECTRON TOMOGRAPHY
Jun Liu 1 , Tao Lin 1 , Douglas J. Botkin 1 , Erin McCrum 1 , Hanspeter Winkler 2 , Steven J. Norris 1
1
Department of Pathology and Laboratory Medicine, University of Texas Medical School at
Houston, Houston, TX 77225-0708, USA.
2
Institute of Molecular Biophysics, Florida State University, Tallahassee, FL, 32306-4380, USA
Motility is often important for virulence of bacterial pathogens, and the flagellum is the
main organelle for motility in bacteria. Bacterial flagella are helical propellers turned by the
flagellar motor, a remarkable nano-machine embedded in the bacterial cell envelope. Powered
by the proton gradient across the cytoplasmic membrane, the motor converts electrochemical
energy into torque through an interaction between a rotating, cylindrical basal body at the end of
the flagellar filament and the stator, a surrounding protein assembly embedded in the
cytoplasmic membrane. Of the 50 genes needed to build a functional flagellum, at least 25
produce proteins essential for flagellar assembly. Although structural studies have revealed the
stunning complexity of the basal body, flagellar assembly and rotation remain poorly understood
at the molecular level, mainly because of the lack of structural information about the membranebound
stators and the torque-generating mechanism in particular. Here, we present the
structures of infectious wild-type and mutant Borrelia burgdoferi organisms and their flagella
motors in situ using high throughput Cryo-Electron Tomography (Cryo-ET). By averaging the 3-
D images of ~1280 flagellar motors, we obtained a ~3 nm resolution model of the combined
stator and rotor structure in its cellular environment. We have also been able to identify
distinctive structural changes resulting from the mutation of a flagellar gene. This is direct
mapping of a single genetic code change into the 3-D structure of a functioning molecular
machine in situ. Our results provide new insights into the motor structure and the molecular
basis for bacterial motility.
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