title: Exchange of rotor components in functioning bacterial flagellar motor.
abstract: The bacterial flagellar motor is a rotary motor driven by the electrochemical potential of a coupling ion. The interaction between a rotor and stator units is thought to generate torque. The overall structure of flagellar motor has been thought to be static, however, it was recently proved that stators are exchanged in a rotating motor. Understanding the dynamics of rotor components in functioning motor is important for the clarifying of working mechanism of bacterial flagellar motor. In this study, we focused on the dynamics and the turnover of rotor components in a functioning flagellar motor. Expression systems for GFP-FliN, FliM-GFP, and GFP-FliG were constructed, and each GFP-fusion was functionally incorporated into the flagellar motor. To investigate whether the rotor components are exchanged in a rotating motor, we performed fluorescence recovery after photobleaching experiments using total internal reflection fluorescence microscopy. After photobleaching, in a tethered cell producing GFP-FliN or FliM-GFP, the recovery of fluorescence at the rotational center was observed. However, in a cell producing GFP-FliG, no recovery of fluorescence was observed. The transition phase of fluorescence intensity after full or partially photobleaching allowed the turnover of FliN subunits to be calculated as 0.0007s(-1), meaning that FliN would be exchanged in tens of minutes. These novel findings indicate that a bacterial flagellar motor is not a static structure even in functioning state. This is the first report for the exchange of rotor components in a functioning bacterial flagellar motor.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Fukuoka
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Inoue
authors.forename: Shun
authors.initials: S
authors.lastname: Terasawa
authors.forename: Hiroto
authors.initials: H
authors.lastname: Takahashi
authors.forename: Akihiko
authors.initials: A
authors.lastname: Ishijima
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism / Q000502:physiology; D004926:Escherichia coli / Q000378:metabolism / Q000502:physiology*; D005407:Flagella / Q000378:metabolism / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D038761:Photobleaching; D012399:Rotation
chemical_list: D001426:Bacterial Proteins; C077389:FliN protein, Bacteria; C075660:Flig protein, Bacteria; C066821:FliM protein, Bacteria; D049452:Green Fluorescent Proteins