MECHANICS OF SINGLE KINESIN MOLECULES MEASURED BY OPTICAL TRAPPING NANOMETRY

We have analyzed the mechanics of individual kinesin molecules by opti cal trapping nanometry. A kinesin molecule was adsorbed onto a latex b ead, which was captured by an optical trap and brought into contact wi th an axoneme that was bound to a glass surface. The displacement of k inesin during force generation was determined by measuring the positio n of the beads with nanometer accuracy. As the displacement of kinesin was attenuated because of the compliance of the kinesin-to-bead and k inesin-to-microtubule linkages, the compliance was monitored during fo rce generation and was used to correct the displacement of kinesin. Th us the velocity and the unitary steps could be obtained accurately ove r a wide force range. The force-velocity curves were linear from 0 to a maximum force at 10 mu M and 1 mM ATP, and the maximum force was sim ilar to 7 pN, which is larger by similar to 30% than values previously reported. Kinesin exhibited forward and occasionally backward stepwis e displacements with a size of similar to 8 nm. The histograms of step dwell time show a monotonic decrease with time. Model calculations in dicate that each kinesin head steps by 16-nm, whereas kinesin molecule steps by 8-nm.