Number of kinesin molecules involved in a bead transport measured by microfluidics and mechanical modeling

In contrast to optical tweezers methods, we established a method to evaluate the adhesion force between a bead carried by multiple kinesins and a microtubule. The method also enables us to estimate the number of kinesins involved in the bead transport. Torque Γ and drag force F D applied by the shearing flow were derived theoretically by the flow rate necessary to break kinesin-microtubule bindings in the bead detachment assay. Based on mechanical modeling, the adhesion force, F Adh , was calculated as 362.9 pN without ATP and 31.3 pN with 1 mM ATP. Furthermore, we found out 5.5–11.9 kinesins are cooperatively working to carry the bead, which is consistent with other results. Our method is advantageous in analyzing multi-kinesin transport system reconstructed in microfluidic systems.