Li Xiang-Dong, Ikebe Reiko, Ikebe Mitsuo
Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
J Biol Chem. 2005 May 6;280(18):17815-22. doi: 10.1074/jbc.M413295200. Epub 2005 Mar 9.
It is known that melanophilin is a myosin Va-targeting molecule that links myosin Va and the cargo vesicles in cells. Here we found that melanophilin directly activates the actin-activated ATPase activity of myosin Va and thus its motor activity. The actin-activated ATPase activity of the melanocyte-type myosin Va having exon-F was significantly activated by melanophilin by 4-fold. Although Rab27a binds to myosin Va/melanophilin complex, it did not affect the melanophilin-induced activation of myosin Va. Deletion of the C-terminal actin binding domain and N-terminal Rab binding domain of melanophilin resulted in no change in the activation of the ATPase by melanophilin, indicating that the myosin Va binding domain (MBD) is sufficient for the activation of myosin Va. Among MBDs, the interaction of MBD-2 with exon-F of myosin Va is critical for the binding of myosin Va and melanophilin, whereas MBD-1 interacting with the globular tail of myosin Va plays a more significant role in the activation of myosin Va ATPase activity. This is the first demonstration that the binding of the cargo molecule directly activates myosin motor activity. The present finding raises the idea that myosin motors are switched upon their binding to the cargo molecules, thus avoiding the waste of ATP consumption.
已知黑素亲和蛋白是一种靶向肌球蛋白Va的分子，它在细胞中连接肌球蛋白Va和货物囊泡。在这里，我们发现黑素亲和蛋白直接激活肌球蛋白Va的肌动蛋白激活的ATP酶活性，从而激活其运动活性。具有外显子F的黑素细胞型肌球蛋白Va的肌动蛋白激活的ATP酶活性被黑素亲和蛋白显著激活了4倍。尽管Rab27a与肌球蛋白Va/黑素亲和蛋白复合物结合，但它并不影响黑素亲和蛋白诱导的肌球蛋白Va的激活。删除黑素亲和蛋白的C末端肌动蛋白结合结构域和N末端Rab结合结构域，黑素亲和蛋白对ATP酶的激活没有变化，这表明肌球蛋白Va结合结构域（MBD）足以激活肌球蛋白Va。在MBD中，MBD-2与肌球蛋白Va的外显子F的相互作用对于肌球蛋白Va和黑素亲和蛋白的结合至关重要，而与肌球蛋白Va的球状尾部相互作用的MBD-1在激活肌球蛋白Va ATP酶活性方面发挥着更重要的作用。这是首次证明货物分子的结合直接激活肌球蛋白的运动活性。目前的发现提出了这样一种观点，即肌球蛋白马达在与货物分子结合时被切换，从而避免了ATP消耗的浪费。
