FBS Colloquia No.330Laboratory of Nano-Biophysics
| Seminar or Lecture |
1. Rotational fluctuations of the E. coli flagellar motor Yumiko Uchida [Specially Appointed Assistant Professor, Laboratory of Nano-Biophysics, Ishijima Lab.] 2. Study of the process of repellent response through the localization of chemoreceptor demethylase CheB Hajime Fukuoka [Associate Professor, Laboratory of Nano-Biophysics, Ishijima Lab.] |
|---|---|
| Date and Time | 27 Jun. 2023 (Tue), 12:15～13:00 |
| Place | 2F Seminar Room, BioSystems Building |
| Language | Japanese |
| Contact |
Hajime Fukuoka |
1. Rotational fluctuations of the E. coli flagellar motor
The flagellum of E. coli is nanomachine for movement, rotating counterclockwise for smooth swimming and clockwise for tumbling (change of swimming direction). The flagellum is composed of three parts; a basal body (motor), a hook (universal joint), and a filament (screw). In our laboratory, we attach microbead to the filament and measure the rotation of the flagellum. In this measurement, we found that the rotational trajectory of the flagellum fluctuates when it rotates counterclockwise. We constructed various mutants to find the cause of fluctuation and measured the rotation using a high-speed camera with a high temporal resolution (12,500 - 21,600 fps). Three results were revealed.
1）Rotational fluctuation is a phenomenon in which the orbit of rotation shrinks randomly and transiently.
2）Rotational fluctuations were observed only during counterclockwise rotation, regardless of the presence or absence of rotational direction change or the structure of flagellar filaments.
3）Rotational fluctuations are not observed in flagella having the straight hook in both clockwise and counterclockwise rotation.
These findings suggest that the structural flexibility of the hook causes a transient shrink of the rotational orbit during counterclockwise rotation. However, the reasons and biological significance still need to be clarified.
2. Study of the process of repellent response through the localization of chemoreceptor demethylase CheB
The escape from dangerous environments is very important property for living organisms. In chemotaxis system, E. coli cells respond to repellent and escape from it, and adapts by resetting the system through the modification of methylation level in MCP by CheR and CheB. The activities of these enzymes are investigated well, on the other hand, the quantitative relation between the intracellular dynamics of those proteins and cellular behavior remains elusive. Therefore, we evaluated the response to repellent (isoleucine) through simultaneously measuring the polar localization of CheB-GFP and the flagellar motor-rotation. In the cell expressing only Tsr (serine receptor), immediately after adding isoleucine, the CheB-localization at cell pole increased and the motor switched to CW rotation. Several tens of seconds, the CheB-localization reduced and the motor gradually resumed rotational switching. These results suggest that the polar localization of CheB represents the active level of polar receptor array. We want to discuss the E. coli repellent response process inferred from the change in the level of polar localization of CheB.
