Kinesin-driven microtubule motility in the presence of alkaline-earth metal ions: Indication for a calcium ion-dependent motility

Abstract

We studied the effect of alkaline–earth metal ions on the kinesin-driven gliding of microtubules, using a narrow glass chamber enabling the exchange of buffer components without interrupting microscopic observation. Under standard conditions (0.5 mM Mg²⁺), microtubules were found to glide at a mean velocity of about 0.6 μm/s. Motility was widely ceased after removing Mg²⁺. Subsequent addition of Ca²⁺ restored motility (maximal mean gliding velocity measured: 0.26 μm/s at 2.5 mM Ca²⁺). Also in the presence of Sr²⁺ or Ba²⁺ a slow gliding could be observed (0.025 μm/s and 0.014 μm/s, respectively, at 0.5 mM). After removal of Ca²⁺, Sr²⁺, or Ba²⁺ and re-addition of Mg²⁺, the gliding velocities reached approximately the values determined under standard conditions. Motility was not changed when 0.5 mM Ca²⁺, Sr²⁺, or Ba²⁺ were applied together with Mg²⁺. Microtubule gliding stopped after substitution of 0.5 mM BeCl₂ for Mg²⁺. When both BeCl₂ and Mg²⁺ were present, the mean gliding velocity was reduced to 0.29 μm/s. In addition, many microtubules were released from the kinesin-coated glass surface, indicating that the beryllium salt disorders the binding between kinesin and microtubules. Our results confirm that Mg²⁺ is the most suitable cofactor for kinesin-driven microtubule motility. However, they also demonstrate that brain kinesin can generate motility when Ca²⁺ was substituted for Mg²⁺. Cell Motil. Cytoskeleton 37:226–231, 1997. © 1997 Wiley-Liss Inc.