Subunit organization and reversal-associated movements in the flagellar switch of Escherichia coli.
Bacterial flagella contain a rotor-mounted protein complex termed the switch complex that functions in flagellar assembly, rotation, and clockwise/counterclockwise direction control. In Escherichia coli and Salmonella, the switch complex contains the proteins FliG, FliM, and FliN and corresponds structurally with the C-ring in the flagellar basal body. Certain features of subunit organization in the switch complex have been deduced previously, but details of subunit organization in the lower part of the C-ring and the molecular movements responsible for motor switching remain unclear. In this study, we use cross-linking, binding, and mutational experiments to examine subunit organization in the bottom of the C-ring and to probe movements that occur upon switching. The results show that FliN tetramers alternate with FliM C-terminal domains to form the bottom of the C-ring in an arrangement that closely reproduces the major features observed in electron microscopic reconstructions. When motors were switched to clockwise rotation by a repellent stimulus, cross-link yields were altered in a pattern indicating relative movement of FliN and FliM(C). These results are discussed in the framework of a structurally grounded hypothesis for the switching mechanism.
Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA.
Mayukh K
MK
Sarkar
Koushik
K
Paul
David F
DF
Blair
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D003545:Cysteine / Q000378:metabolism; D004252:DNA Mutational Analysis; D004220:Disulfides / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism*; D005407:Flagella / Q000187:drug effects / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009068:Movement / Q000187:drug effects; D010641:Phenotype; D011485:Protein Binding / Q000187:drug effects; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism*; D012399:Rotation; D040681:Structural Homology, Protein; D013499:Surface Properties / Q000187:drug effects
D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D004220:Disulfides; C077389:FliN protein, Bacteria; D021122:Protein Subunits; C066821:FliM protein, Bacteria; D003545:Cysteine