Motor Max Force Max Speed Max Power
ROTARY
Flagellar motor (8 units, E. coli)
2400 pN nm
95 pN
300 Hz
35 m/s
2000 pN nm @ 150 Hz
1.9 x 106 pN nm /s
(Vibrio) 1700 Hz
220 m/s
(single unit) 300 pN nm
12 pN
300 Hz
35 m/s
250 pN nm @ 150 Hz
2.4 x 105 pN nm /s
F1 -ATPase 40 pN nm
40 pN
150 Hz
0.9 m/s
20 pN nm @ 75 Hz
9 x 103 pN nm /s
LINEAR
Myosin (single molecule in muscle or in vitro)
6 pN 10 m/s(speed of array, each
molecule mostly detached)
2 pN @ 10 /s x 20 nm
400 pN nm /s
Kinesin 5 pN 1 m/s 2.5 pN @ 0.5 m /s
1.25 x 103 pN nm /s
RNA polymerase
20 pN 0.01 m/s ~200 pN nm /s
Overview of lectures
• BIOLOGY was introduced by Judy Armitage’s
• BIOPHYSICS - Experimental Techniques to measure rotary molecular motors
Flagellar Motor
F1-ATPase
Single-molecule experiments on bacterial flagellar motors
Rotor
Stator
Continuous switch model
Switching
F Bai, RW. Branch, D Nicolau, TPilizota, BC Steel, PK Maini, RM Berry (2010)Conformational spread as a mechanism for cooperativity in the bacterial flagellar switchScience 327:685-689
Bacterial Chemotaxis
1-D Ising model of flagellar switch
movie
Tethered cells
Cell body rotates at ~ 10 Hz
1 m
Flagellum tethered to coverslip
Cell body
Coverslip in microscope
Frequency (Hz)
fast beads, small.mov
Work = torque x angle
Torque = d(work) / d(angle)
Low Reynolds number:Torque = viscous drag coefficient x angular velocity
Beads attached to the motor
Finite, variable switch times
Switch times distribution predicted by model
… further detailed tests of model
C / Co
Resurrection
resurrection
steady-state expression
One motor can contain at least 11 stators
1 m bead
0.3 m bead
Torque-versus speed
Stepping rotation
Speed control for step detection using sodium-driven chimaera
pmf or smf = Vm + kT/e ln (Cin/Cout)
Low numbers of stators:
Low-level induction of stator proteins
De-energization also affects stator number
Slow rotation with (probably) one stator unit
Back-focal plane detection Fluorescence detection
Real speed 30x slower
26 steps per revolution
Kinesin, myosin II, Myosin V, F1-ATPase:
Step size is set by the track
by energy conservation based on full energization and high loads, one proton gives a max step size of ~10 degrees. Maybe there are 2 ions per step?
34-fold model refines C-ring : 25-fold model refines M ring (& C-inner)Thomas et al 2006
One ATP per step
ATP
ADP+ Pi
10nm
F1
FO
H+ or Na+
Single-molecule experiments on ATP-synthase
F1
Biotin-avidin link to rotating handle(actin filament, beads)
His-tag link to surface
0.5 micron beadsRotated by F1
Fluorescent actin filamentRotated by F1
(movie: Wolfgang Junge)
High [ATP] : no wait before 90° step
Medium [ATP] : ~ms before 90° step
Low [ATP] : long wait before 90° step
(ms)
All [ATP] : ~ms before 30° step
Low [ATP] : - 90° step rate-limiting- exponential distribution- single step
High [ATP] : - 30° step rate-limiting- peaked distribution- double (or more) step