Processive movement of single kinesins on crowded microtubules visualized using quantum dots.
Kinesin-1 is a processive molecular motor transporting cargo along microtubules. Inside cells, several motors and microtubule-associated proteins compete for binding to microtubules. Therefore, the question arises how processive movement of kinesin-1 is affected by crowding on the microtubule. Here we use total internal reflection fluorescence microscopy to image in vitro the runs of single quantum dot-labelled kinesins on crowded microtubules under steady-state conditions and to measure the degree of crowding on a microtubule at steady-state. We find that the runs of kinesins are little affected by high kinesin densities on a microtubule. However, the presence of high densities of a mutant kinesin that is not able to step efficiently reduces the average speed of wild-type kinesin, while hardly changing its processivity. This indicates that kinesin waits in a strongly bound state on the microtubule when encountering an obstacle until the obstacle unbinds and frees the binding site for kinesin's next step. A simple kinetic model can explain quantitatively the behaviour of kinesin under both crowding conditions.
Seitz
Arne
A
European Molecular Biology Laboratory, Cell Biology and Biophysics Unit, Heidelberg, Germany.
Surrey
Thomas
T
D001692:Biological Transport / Q000502:physiology; D049452:Green Fluorescent Proteins; D016547:Kinesins / Q000378:metabolism*; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000378:metabolism*; D008954:Models, Biological; D020409:Molecular Motor Proteins / Q000378:metabolism*; D045663:Quantum Dots
D020409:Molecular Motor Proteins; D049452:Green Fluorescent Proteins; D016547:Kinesins