Lecture 6 Biomotors

Self assembling rotary motors

Examples of Biomolecular Motors

Karplus and Gao, Curr Opin. Struct. Biol (2004) 250-259

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,

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ADP + Phosphate ATP + H2O

ATPase - the movie

What does the whole motor look like?

The proton-driven torque generator

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Kinosita Lab

Nature (1997) 386, 299-302

Single molecule motor nanotechnology

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Kinosita Lab

Nature (2001) 410, 898-904

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) anddeduced rotational potential (b). Colored lines in b represent the angle dependent potential energy for subunit rotation.(A)-(A’) are potential energies for thecorresponding 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 Zn2+ control of motor

Molecular baton twirling

Cell motility is driven by larger ion-driven molecular motors

Bacterial Flagellar

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Driving Force Proton or sodium electrochemical gradientNumber of Protons per revolution ~ 1000(energy per proton) ~ 2.5 x 10-20 J (6kT)Maximum rotation rate 300 Hz (protons) 1700 Hz (sodium)Torque at stall ~ 4 x 10-18 Nm (4nN.nm)Maximum power output ~ 10-15 WEfficiency 50-100% (stall) ~ 5% (swimming cell)Number of steps per revolution ~ 50 per torque generatorLinear velocity of cells <100µm s-1

Force/speed measurements on Flagellar - twirling cells