Single Molecule Fluorescence and Optical Trapping Applied to Molecular Motors: Two can do it better than one.
KTH Applied Physics seminars
Monday 10 December 2012
to 16:00 at
Paul Selvin (Physics & Biophysics, Loomis Lab of Physics, University of Illinois)
Kinesin and dynein are molecular motors that move in opposite directions on a microtubule. They often act on the same cargo, causing the cargo to frequently switch direction.
Whether this back-and-forth motion results from a coordinating complex or from a tug-of-war between the two motors is currently unknown. We have applied single molecule fluorescence to determine that they are undergoing a synergistic tug-of-war. By synergistic, we mean that the combination of the two motors is able to bypass roadblocks along the microtubule. Furthermore, using an in vivo optical trap, and by comparing directional stall forces in vivo and in vitro, we found when cargo is going in the positive microtubule direction, kinesin and dynein are pulling, with the dynein walking backwards. The net stall force equals the stall force of kinesin (≈ 7 pN) minus the stall forces of the number of dyneins (1.1 pN x ND, where ND, = 0 to 6). When moving in the negative microtubule direction, the stall force is just equal to a multiple of dynein’s stall force (1.1 pN x ND), implying that kinesin has fallen off the microtubule.