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People
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Junhua YuanPostdoctoral Fellow, working on properties of the flagellar motor near zero load. Motor force generation: Behavior near zero load. Junhua attached 60 nm gold beads to flagellar hooks (of cells lacking flagellar filaments) and followed their rotation by imaging scattered laser light on a pinhole in front of a photomultiplier. At room temperature, the beads spun ~ 300 Hz. Now, in a resurrection experiment (when bad force-generating units were replaced by good ones) full speed was restored in a single step. This method was also utilized to look at the temperature & solvent-isotope effects on the flagellar motor near zero load. We monitored changes in speed when cells were subjected to changes in temperature or shifted from a medium made with H2O to one made with D2O. In H2O, the speed increased with temperature in a near-exponential manner, with an activation enthalpy of 52 ± 4 kJ/mol (12.0 ± 1.0 kcal/mol). In D2O, the speed increased in a similar manner, with an activation enthalpy of 50 ± 4 kJ/mol. The speed in H2O was higher than that in D2O by a factor 1.53 ± 0.14. Motor switching under load Recently, in collaboration with Karen Fahrner, Junhua examined motor switching at low loads, by attaching 100-200 nm gold beads to flagellar hooks and monitoring their direction of rotation in media containing different concentrations of the viscous agent Ficoll. Contrary to the case at high loads, motor switching rates increased appreciably with load. Both the CW to CCW and CCW to CW switching rates increased linearly with motor torque. Evidently, the switch senses stator–rotor interactions as well as the CheY-P concentration. References:Yuan, J., Fahrner, K. A., Turner, L. and Berg, H. C. Asymmetry in the clockwise and counter-clockwise rotation of the bacterial flagellar motor. Proc. Natl. Acad. Sci. USA 107, 12846-12949 (2010). Yuan, J. and Berg, H. C. Temperature and solvent-isotope effects on the flagellar rotary motor near zero load. Biophys J. 98, 2121-2126 (2010). Yuan, J., Fahrner, K. A. and Berg, H. C. Switching of the bacterial flagellar motor near zero load. J. Mol. Biol. 390, 394-400 (2009). Yuan, J., and Berg, H.C. Following the behavior of the flagellar rotary motor near zero load. Exp. Mech. (published online 09 September 2009). Yuan, J. and Berg, H.C. Resurrection of the flagellar rotary motor near zero load. Proc Natl. Acad. Sci. USA 105, 1182-1185 (2008).
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Last modified Wednesday, April 21, 2010.
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