title: Self-organization of actin networks by a monomeric myosin.
abstract: 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.
authors.affiliation: Department of Cellular Physiology, Ludwig-Maximilians-Universität München, 80336 Munich, Germany.|Center for Nanosciences München, 80799 Munich, Germany.
authors.forename: Dario
authors.initials: D
authors.lastname: Saczko-Brack
authors.affiliation: Department of Cellular Physiology, Ludwig-Maximilians-Universität München, 80336 Munich, Germany.|Center for Nanosciences München, 80799 Munich, Germany.
authors.forename: Ewa
authors.initials: E
authors.lastname: Warchol
authors.affiliation: Department of Cellular Physiology, Ludwig-Maximilians-Universität München, 80336 Munich, Germany.|Center for Nanosciences München, 80799 Munich, Germany.
authors.forename: Benoit
authors.initials: B
authors.lastname: Rogez
authors.affiliation: Department of Cellular Physiology, Ludwig-Maximilians-Universität München, 80336 Munich, Germany.|Center for Nanosciences München, 80799 Munich, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Kröss
authors.affiliation: Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, NIH, Bethesda, MD 20892.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Heissler
authors.affiliation: Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, NIH, Bethesda, MD 20892.
authors.forename: James R
authors.initials: JR
authors.lastname: Sellers
authors.affiliation: Department of Cellular Physiology, Ludwig-Maximilians-Universität München, 80336 Munich, Germany; claudia.veigel@med.uni-muenchen.de chris.batters@med.uni-muenchen.de.|Center for Nanosciences München, 80799 Munich, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Batters
authors.affiliation: Department of Cellular Physiology, Ludwig-Maximilians-Universität München, 80336 Munich, Germany; claudia.veigel@med.uni-muenchen.de chris.batters@med.uni-muenchen.de.|Center for Nanosciences München, 80799 Munich, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Veigel
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry*; D000199:Actins / Q000737:chemistry*; D000205:Actomyosin / Q000737:chemistry; D000251:Adenosine Triphosphatases / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D002147:Calmodulin / Q000737:chemistry; D002465:Cell Movement; D020690:GTPase-Activating Proteins / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008854:Microscopy, Electron; D008870:Microtubules / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D009218:Myosins / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence
chemical_list: D000199:Actins; D002147:Calmodulin; D020690:GTPase-Activating Proteins; C120896:MYO9A protein, human; D000255:Adenosine Triphosphate; D000205:Actomyosin; D000251:Adenosine Triphosphatases; D009218:Myosins
keywords: actin network; electron microscopy; unconventional myosin