Probing the binding force in a Tau-Microtubule bundle*

Microtubules are the biopolymer “bones” of the cell. Multiple microtubules can associate into bundles, which contribute to cellular structure and mechanics in contexts such as the mitotic spindle, cilia/flagella, and the axon initial segment of neurons. However, the mechanical stability of microtubule bundles remains unclear. To address this question, we use nature’s nanomachine, the kinesin motor protein, to exert force on individual microtubules within a bundle and to probe the force that holds microtubules together in a bundle. Specifically, we use the neuronal protein tau to bundle microtubules in well-controlled, cell-free environments, and we employ fluorescence microscopy to determine the number of microtubules in individual bundles and to visualize the real-time movement of individual microtubules being pulled from individual tau-microtubule bundles. Our preliminary data indicate an ~pN binding force for the tau-microtubule bundles. These findings provide important new data on the mechanical stability of microtubule bundles.