Taft Manuel H, Hartmann Falk K, Rump Agrani, Keller Heiko, Chizhov Igor, Manstein Dietmar J, Tsiavaliaris Georgios
Institute for Biophysical Chemistry, OE 4350, Hannover Medical School, Feodor-Lynen-Str. 5, D-30625 Hannover, Germany.
J Biol Chem. 2008 Oct 3;283(40):26902-10. doi: 10.1074/jbc.M802957200. Epub 2008 Jul 23.
Dictyostelium myosin-5b is the gene product of myoJ and one of two closely related myosin-5 isoenzymes produced in Dictyostelium discoideum. Here we report a detailed investigation of the kinetic and functional properties of the protein. In standard assay buffer conditions, Dictyostelium myosin-5b displays high actin affinity in the presence of ADP, fast ATP hydrolysis, and a high steady-state ATPase activity in the presence of actin that is rate limited by ADP release. These properties are typical for a processive motor that can move over long distances along actin filaments without dissociating. Our results show that a physiological decrease in the concentration of free Mg(2+)-ions leads to an increased rate of ADP release and shortening of the fraction of time the motor spends in the strong actin binding states. Consistently, the ability of the motor to efficiently translocate actin filaments at very low surface densities decreases with decreasing concentrations of free Mg(2+)-ions. In addition, we provide evidence that the observed changes in Dd myosin-5b motor activity are of physiological relevance and propose a mechanism by which this molecular motor can switch between processive and non-processive movement.
盘基网柄菌肌球蛋白-5b是肌动蛋白J的基因产物，是在盘基网柄菌中产生的两种密切相关的肌球蛋白-5同工酶之一。在此，我们报告了对该蛋白质的动力学和功能特性的详细研究。在标准测定缓冲液条件下，盘基网柄菌肌球蛋白-5b在存在ADP的情况下表现出高肌动蛋白亲和力、快速ATP水解，并且在存在肌动蛋白时具有高稳态ATP酶活性，其速率受ADP释放限制。这些特性是一种持续性马达的典型特征，该马达可以沿着肌动蛋白丝长距离移动而不解离。我们的结果表明，游离Mg(2+)离子浓度的生理下降导致ADP释放速率增加，并且马达在强肌动蛋白结合状态下花费的时间分数缩短。一致地，随着游离Mg(2+)离子浓度的降低，马达在非常低的表面密度下有效转运肌动蛋白丝的能力下降。此外，我们提供证据表明，观察到的盘基网柄菌肌球蛋白-5b马达活性变化具有生理相关性，并提出了一种该分子马达可以在持续性和非持续性运动之间切换的机制。
