Unbinding strength between C-terminal segment of AtMAP65-1 and microtubule studied with dual-optical tweezers

It has been reported that AtMAP65-1 dimer induces the formation of large microtubule bundles by forming cross-bridges between microtubules. More important, it has been reported that the C terminus of AtMAP65-1 contributes to microtubule binding and the N terminus to AtMAP65-1 dimerization. The interaction between microtubule and AtMAP65-1 is crucial since it can directly affect mechanical properties of microtubules and further the organizations and some functions of microtubules. In order to quantitatively know the interaction between microtubule and the C-terminal segment of microtubule associated protein (AtMAP65-1), we measure the unbinding force between them with dual-optical tweezers. Force histograms reveal quantized force distributions. Based on Bell-Evans-model of multiple bonds, histograms are fitted and kinetic parameters are obtained. The most probable unbinding force for the single bond is 20.0plusmn1.1 pN. Position of transition state of the bond is given to be Deltax=2.1 plusmn 0.1 nm. Intrinsic dissociation rate constant k₀ is 0.0002plusmn0.00005 s^-1.