Lecture 6 Biomotors Self assembling rotary motors

Examples of Biomolecular Motors Karplus and Gao, Curr Opin. Struct. Biol (2004)

Proton gradients generated by electron transfer

The smallest rotary motor self-assembles from 8 proteins

ATPase has identifiable motor parts Motor, Drive shaft, Cam, Stator, Viscous coupling,

ADP + Phosphate ATP + H 2 O ATPase - the movie

What does the whole motor look like?

The proton-driven torque generator

Kinosita Lab Nature (1997) 386, Single molecule motor nanotechnology

Kinosita Lab Nature (2001) 410, ATPase is a stepper motor

Substeps in the rotation of F1-ATPase at 20 µM ATP. Long dashed lines are drawn at intervals of 120˚, and dotted lines are drawn 30˚ below the dashed lines. Kinetics of substeps (a) and deduced rotational potential (b). Colored lines in b represent the angle dependent potential energy for  subunit rotation. (A)-(A’) are potential energies for the corresponding chemical states in a. Adapted from ref. 7. Average torque during each revolution is 50pN.nm, but this is distributed over sub- steps. ATPase is a variable step stepper motor

Montemagno Lab Science (2000) 290, p1555 Nature Materials (2002) 1, p173 Zn 2+ control of motor Molecular baton twirling

Cell motility is driven by larger ion-driven molecular motors Bacterial Flagellar

Flagellar

Driving Force Proton or sodium electrochemical gradient Number of Protons per revolution ~ 1000 (energy per proton) ~ 2.5 x J (6kT) Maximum rotation rate 300 Hz (protons) 1700 Hz (sodium) Torque at stall ~ 4 x Nm (4nN.nm) Maximum power output ~ W Efficiency % (stall) ~ 5% (swimming cell) Number of steps per revolution ~ 50 per torque generator Linear velocity of cells<100µm s -1 Force/speed measurements on Flagellar - twirling cells