title: Signal-dependent turnover of the bacterial flagellar switch protein FliM.
abstract: Most biological processes are performed by multiprotein complexes. Traditionally described as static entities, evidence is now emerging that their components can be highly dynamic, exchanging constantly with cellular pools. The bacterial flagellar motor contains approximately 13 different proteins and provides an ideal system to study functional molecular complexes. It is powered by transmembrane ion flux through a ring of stator complexes that push on a central rotor. The Escherichia coli motor switches direction stochastically in response to binding of the response regulator CheY to the rotor switch component FliM. Much is known of the static motor structure, but we are just beginning to understand the dynamics of its individual components. Here we measure the stoichiometry and turnover of FliM in functioning flagellar motors, by using high-resolution fluorescence microscopy of E. coli expressing genomically encoded YPet derivatives of FliM at physiological levels. We show that the approximately 30 FliM molecules per motor exist in two discrete populations, one tightly associated with the motor and the other undergoing stochastic turnover. This turnover of FliM molecules depends on the presence of active CheY, suggesting a potential role in the process of motor switching. In many ways the bacterial flagellar motor is as an archetype macromolecular assembly, and our results may have further implications for the functional relevance of protein turnover in other large molecular complexes.
authors.affiliation: Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: Nicolas J
authors.initials: NJ
authors.lastname: Delalez
authors.forename: George H
authors.initials: GH
authors.lastname: Wadhams
authors.forename: Gabriel
authors.initials: G
authors.lastname: Rosser
authors.forename: Quan
authors.initials: Q
authors.lastname: Xue
authors.forename: Mostyn T
authors.initials: MT
authors.lastname: Brown
authors.forename: Ian M
authors.initials: IM
authors.lastname: Dobbie
authors.forename: Richard M
authors.initials: RM
authors.lastname: Berry
authors.forename: Mark C
authors.initials: MC
authors.lastname: Leake
authors.forename: Judith P
authors.initials: JP
authors.lastname: Armitage
mesh_terms: D000465:Algorithms; D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005407:Flagella / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D008565:Membrane Proteins / Q000378:metabolism; D000072236:Methyl-Accepting Chemotaxis Proteins; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D020409:Molecular Motor Proteins / Q000737:chemistry; D016011:Normal Distribution; D015398:Signal Transduction; D013269:Stochastic Processes; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D020409:Molecular Motor Proteins; C000607606:cheY protein, E coli; C066821:FliM protein, Bacteria