期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：52
页码：E8387-E8395
DOI：10.1073/pnas.1612719113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceActomyosin networks are central to a broad range of cellular motile processes, including cell polarization and collective cell migration during morphogenesis and development. Myosin-IXa is critically involved in these processes. Using fluorescence spectroscopy, total internal reflection fluorescence, and electron microscopy, we demonstrate that myosin-IXa assembles actin filaments into highly ordered lattices. The actin filaments of parallel polarity are connected by myosin-IXa in distinct conformations and at a repeat distance of 36 nm across the network. The myosin-IXa-induced actin lattices introduce orientated actin tracks and a network of regularly spaced platforms for localized Rho-GTPase-activating protein activity in cell polarization and collective cell migration. The organization of actomyosin networks lies at the center of many types of cellular motility, including cell polarization and collective cell migration during development and morphogenesis. Myosin-IXa is critically involved in these processes. Using total internal reflection fluorescence microscopy, we resolved actin bundles assembled by myosin-IXa. Electron microscopic data revealed that the bundles consisted of highly ordered lattices with parallel actin polarity. The myosin-IXa motor domains aligned across the network, forming cross-links at a repeat distance of precisely 36 nm, matching the helical repeat of actin. Single-particle image processing resolved three distinct conformations of myosin-IXa in the absence of nucleotide. Using cross-correlation of a modeled actomyosin crystal structure, we identified sites of additional mass, which can only be accounted for by the large insert in loop 2 exclusively found in the motor domain of class IX myosins. We show that the large insert in loop 2 binds calmodulin and creates two coordinated actin-binding sites that constrain the actomyosin interactions generating the actin lattices. The actin lattices introduce orientated tracks at specific sites in the cell, which might install platforms allowing Rho-GTPase-activating protein (RhoGAP) activity to be focused at a definite locus. In addition, the lattices might introduce a myosin-related, force-sensing mechanism into the cytoskeleton in cell polarization and collective cell migration.
