Dunn Brian D, Sakamoto Takeshi, Hong Myoung-Soon S, Sellers James R, Takizawa Peter A
Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.
J Cell Biol. 2007 Sep 24;178(7):1193-206. doi: 10.1083/jcb.200707080.
The yeast Saccharomyces cerevisiae uses two class V myosins to transport cellular material into the bud: Myo2p moves secretory vesicles and organelles, whereas Myo4p transports mRNA. To understand how Myo2p and Myo4p are adapted to transport physically distinct cargos, we characterize Myo2p and Myo4p in yeast extracts, purify active Myo2p and Myo4p from yeast lysates, and analyze their motility. We find several striking differences between Myo2p and Myo4p. First, Myo2p forms a dimer, whereas Myo4p is a monomer. Second, Myo4p generates higher actin filament velocity at lower motor density. Third, single molecules of Myo2p are weakly processive, whereas individual Myo4p motors are nonprocessive. Finally, Myo4p self-assembles into multi-motor complexes capable of processive motility. We show that the unique motility of Myo4p is not due to its motor domain and that the motor domain of Myo2p can transport ASH1 mRNA in vivo. Our results suggest that the oligomeric state of Myo4p is important for its motility and ability to transport mRNA.
酿酒酵母利用两种V类肌球蛋白将细胞物质运输到芽中：肌球蛋白2（Myo2p）负责运输分泌囊泡和细胞器，而肌球蛋白4（Myo4p）则运输信使核糖核酸（mRNA）。为了解Myo2p和Myo4p如何适应运输物理性质不同的货物，我们在酵母提取物中对Myo2p和Myo4p进行了表征，从酵母裂解物中纯化出活性Myo2p和Myo4p，并分析了它们的运动性。我们发现Myo2p和Myo4p之间存在几个显著差异。首先，Myo2p形成二聚体，而Myo4p是单体。其次，在较低的马达密度下，Myo4p能产生更高的肌动蛋白丝速度。第三，Myo2p的单分子具有较弱的持续性，而单个Myo4p马达则没有持续性。最后，Myo4p能自组装成具有持续性运动能力的多马达复合体。我们表明，Myo4p独特的运动性并非源于其马达结构域，并且Myo2p的马达结构域在体内能够运输ASH1 mRNA。我们的结果表明，Myo4p的寡聚状态对其运动性和运输mRNA的能力很重要。
