POSTERS - BLAST X - University of Utah

BLAST X Poster #28
TORQUE RESPONSE OF THE SODIUM-DRIVEN CHIMERIC FLAGELLAR MOTOR IN
E.COLI INDUCED BY REVERSIBLE TEMPERATURE CHANGE
Yuichi Inoue (1), Kuniaki Takeda (2), Hajime Fukuoka (1), Hiroto Takahashi (1) and Akihiko
Ishijima (1).
1: IMRAM, Tohoku University; 2: Graduate School of Life Sciences, Tohoku University, Katahira
2-1-1, Aoba-ku, Sendai 980-8577, Japan
Mechanical step of motor proteins is a key to understand the molecular mechanism of
energy transduction from chemical energy into mechanical work. We have demonstrated the 26
steps in a rotation of Na + -driven chimeric flagellar motor (Sowa et al., 2005) and the torquespeed
relationship (Inoue et al., 2008) using back-focal-plane interferometry. However, present
time resolution is not enough to understand molecular mechanism of the steps of motor proteins
including not only flagellar motors but also linear motors as skeletal myosin. One possible option
would be to slow down the temperature-dependent processes in a chemo-mechanical cycle by
reducing temperature.
We report the cooling experiment with a water-cooling chip in a simple and reversible
way. A small chip of ~18mm*18mm*2mm was made with glass cover slides and plastic tubes to
lead cooling water. This chip was made direct contact on a sample chamber and placed in the
light axis of the microscope. By changing temperature of the cooling flow, sample temperature
from 23 to -8 degree Celsius was monitored using thermocouple. Temperature change could be
applied repeatedly in a time constant < 60 sec.
Simultaneous measurement of the motor speed and sample temperature showed the
speed change as reported for low temperature (Chen and Berg, 2000). With increasing
temperature with hot water, however, sudden drop of speed was measured over ~40 deg C.
When the temperature returned back to room temperature, the speed was restored mostly in
several minutes. The drop and recovery of the speed were coincided with stepwise change in
the generated torque.
These results suggest that our cooling system is useful not only for the cooling
experiment for improving time resolution but also for the heating experiment to understand heat
resistance which might be related to stator dynamics.
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