Nucleotide dependent changes in the stiffness of single kinesin molecules

The goal of our study was to characterize the elastic properties of individual kinesin molecules in different nucleotide states as they interact with microtubules. We sparsely adsorbed kinesin molecules to nanometer-sized microspheres and recorded thermally driven position fluctuations of the microspheres with a three-dimensional position detection system that allows to monitor movements in x-, y-, and z-direction. Upon binding of single kinesin molecules to immobilized microtubules the thermally driven position fluctuations of the microspheres change significantly. Recording thermally driven position fluctuations in the absence or presence of ATP, or with different ATP-analogues, the stiffness of the tethering kinesin molecule in different nucleotide states can be derived from the 3D position fluctuations. In the absence of ATP the axial stiffness of kinesin was found to be ~ 0.04 and 0.07 pN/nm, possibly representing single- and double-headed binding, respectively. At low ATP concentrations the axial stiffness of kinesin increased to values of 0.125 pN/nm. Comparable values of 0.146 pN/nm and 0.149 pN/nm were found in the presence of the non- or slowly hydrolysable ATP-analogues AMP-PNP and ATPγS, respectively. These findings show that the stiffness of the kinesin-microtubule complex is different for at least some of the intermediates in the ATPase cycle of kinesin. Recording of thermally driven fluctuations in x-, y-, and z-direction also allow to derive geometrical properties of the kinesin molecules that tether microspheres to immobilized microtubules. Our data reveal a total linker length of ~ 70 nm with a free hinge located ~ 10 nm above the microtubule. This pivot location coincides with the neck linker or neck region of the kinesin molecules