Cryoelectron tomography reveals the sequential assembly of bacterial flagella in Borrelia burgdorferi.
Periplasmic flagella are essential for the distinctive morphology, motility, and infectious life cycle of the Lyme disease spirochete Borrelia burgdorferi. In this study, we genetically trapped intermediates in flagellar assembly and determined the 3D structures of the intermediates to 4-nm resolution by cryoelectron tomography. We provide structural evidence that secretion of rod substrates triggers remodeling of the central channel in the flagellar secretion apparatus from a closed to an open conformation. This open channel then serves as both a gateway and a template for flagellar rod assembly. The individual proteins assemble sequentially to form a modular rod. The hook cap initiates hook assembly on completion of the rod, and the filament cap facilitates filament assembly after formation of the mature hook. Cryoelectron tomography and mutational analysis thus combine synergistically to provide a unique structural blueprint of the assembly process of this intricate molecular machine in intact cells.
Department of Pathology and Laboratory Medicine, University of Texas Health Science Center, Houston, TX 77030, USA.
Xiaowei
X
Zhao
Kai
K
Zhang
Tristan
T
Boquoi
Bo
B
Hu
M A
MA
Motaleb
Kelly A
KA
Miller
Milinda E
ME
James
Nyles W
NW
Charon
Michael D
MD
Manson
Steven J
SJ
Norris
Chunhao
C
Li
Jun
J
Liu
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D025065:Borrelia burgdorferi / Q000235:genetics / Q000378:metabolism*; D005407:Flagella / Q000378:metabolism*; D009154:Mutation; D011487:Protein Conformation; D014054:Tomography / Q000379:methods*
D001426:Bacterial Proteins
bacterial motility; macromolecular assemblages; molecular machines; protein secretion