Lecture 24 Tubulin and Microtubule dynamics

MW 55000 a-tubulin 8 genes b-tubulin 9 genes In humans

g-Tubulin Ring Complex

Microtubule-associated proteins (MAPs) stabilizing EB1-decorates tips

Kinesin was discovered in the cytoplasm of giant squid axon

40 Kinesin genes in humans

a, Sample record from the force clamp, showing kinesin-driven bead movement and corresponding optical trap displacement (2 mM ATP). Discrete steps of 8 nm are readily apparent. Inset, schematic representation of the motility assay used. The separation between bead and trap was nominally fixed at x = 175 nm. Visscher et al., 1999 Nature 400, 184-189

Stall force = ~5 pN, Mechanical work equals force times distance, Kinesin-1 has just one binding site per tubulin dimer; the motor takes 8-nm steps from one tubulin dimer; each step corresponds to one cycle of the ATPase reaction.                                                         By tethering single molecules of Kinesin-1 to tiny tensiometers - a flexible glass rod or an optical trap - it is possible to measure the force exerted by a single Kinesin-1 molecule. Stall force = ~5 pN, Mechanical work equals force times distance, Kinesin-1 can do ~40 x 10-21 J of work per step, and if there is just one ATP consumed per step, then the efficiency is ~40%. http://www.proweb.org/kinesin/KinesinMotility.html

Dynein

The Dynactin complex

Chlamidomonas Sperm

Cilia/flagella dynein

Intraflagellar transport (IFT)