Self-assembly of the filament capping protein, FliD, of bacterial flagella into an annular structure.
A bacterial flagellum has a cap structure at the tip of the external filament. The cap is composed of the FliD protein (Mr, 49 x 10(3)), and plays an essential role in the polymerization of the filament protein, flagellin, which is believed to be transported through a central channel in the flagellum. A fliD-deficient mutant becomes non-motile because it lacks flagellar filaments and leaks flagellin monomer out into the medium. We have constructed a FliD-overproducing plasmid and purified the protein. The purified FliD at high concentration formed a large complex (Mr, ca. 600 x 10(3)) under physiological conditions. The complex was found by electron microscopy to be ring shaped. Image analysis revealed that the complex consisted of five substructures arranged in a pentagonal shape. Its outer diameter, approximately 10 nm, was about the same as that of the cap at the tip of the wild-type flagella. When the annular structure was added to the culture medium of a Salmonella fliD mutant, almost all of the cells became able to swim. Overall, about ten molecules of FliD self-assemble into an annular structure in vitro, forming the functional capping structure by incorporating flagellin at the tip of the flagellar filament in vivo.
Ikeda
T
T
Department of Microbiology, School of Dentistry, Aichi-Gakuin University, Nagoya, Japan.
Oosawa
K
K
Hotani
H
H
D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism* / Q000648:ultrastructure; D002850:Chromatography, Gel; D003001:Cloning, Molecular; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics; D005407:Flagella / Q000378:metabolism*; D015870:Gene Expression / Q000235:genetics; D008854:Microscopy, Electron; D008958:Models, Molecular; D008970:Molecular Weight; D010957:Plasmids / Q000235:genetics; D011487:Protein Conformation; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism* / Q000502:physiology
D001426:Bacterial Proteins; C076733:FlaD protein, Bacteria