细胞内物质转运和定位依赖于细胞骨架及其马达蛋白。非典型肌球蛋白是一类重要的马达蛋白，可以将ATP水解产生的化学能转化成机械能，驱动运载货物沿微丝运动。哺乳动物Myosin-Va（Myo5a）属于第五类非典型肌球蛋白，在黑色素细胞中参与黑色素囊泡的转运和定位。Myo5a通过其尾部与货物介导蛋白结合，实现与黑色素囊泡连接。我们发现Myo5a的尾部具有抑制马达头部的功能，钙离子和货物介导蛋白的结合可以解除尾部抑制，激活马达活性。在此基础上，我们提出钙离子和货物介导蛋白协同调节Myo5a马达功能的模型。本项目将验证该模型，阐明Myo5a的调节机制，研究目标包括：1）确定维持Myo5a折叠抑制状态的结构基础；2）揭示多种货物介导蛋白协同调控Myo5a马达功能的分子机制；3）阐明钙离子协同货物介导蛋白调控Myo5a马达功能的分子机制。本研究将揭示Myo5a的调节机制，为细胞内物质转运研究提供新思路。

Cytoskeleton and motor proteins play a critical role in intracellular trafficking. Unconventional myosin is an actin-based motor protein which is capable of converting the energy from ATP hydrolysis into mechanical movement along actin filament. Mammalian Myo5a belongs to class V myosin. In melanocytes, Myo5a participates in the intracellular trafficking of melanosomes. The docking of Myo5a onto melanosome is mediated by the interaction between the tail domain of Myo5a and cargo adaptors. We found that the tail domain of Myo5a is the inhibitory domain and that calcium and cargo adaptor are able to relief the tail inhibition, thus activating the motor function. Based on those findings, we propose that the motor function of Myo5a is co-regulated by calcium and cargo adaptors. The proposed project will test our hypothesis and clarify the molecular mechanism of Myo5a regulation. The specific aims are as follows. 1) Determine the structural basis of Myo5a in the folded, inhibited state. 2) Establish the co-regulation of Myo5a by multiple cargo adaptors. 3) Establish the co-regulation of Myo5a by calcium and cargo adaptors. The proposed project will not only deepen our understanding of structure and function of Myo5a, but also shed light on the molecular mechanism of intracellular trafficking.