title: Calcium can mobilize and activate myosin-VI.
abstract: The ability to coordinate the timing of motor protein activation lies at the center of a wide range of cellular motile processes including endocytosis, cell division, and cancer cell migration. We show that calcium dramatically alters the conformation and activity of the myosin-VI motor implicated in pivotal steps of these processes. We resolved the change in motor conformation and in structural flexibility using single particle analysis of electron microscopic data and identified interacting domains using fluorescence spectroscopy. We discovered that calcium binding to calmodulin increases the binding affinity by a factor of 2,500 for a bipartite binding site on myosin-VI. The ability of calcium-calmodulin to seek out and bridge between binding site components directs a major rearrangement of the motor from a compact dormant state into a cargo binding primed state that is nonmotile. The lack of motility at high calcium is due to calmodulin switching to a higher affinity binding site, which leaves the original IQ-motif exposed, thereby destabilizing the lever arm. The return to low calcium can either restabilize the lever arm, required for translocating the cargo-bound motors toward the center of the cell, or refold the cargo-free motors into an inactive state ready for the next cellular calcium flux.
authors.affiliation: Department of Cellular Physiology, Ludwig-Maximilians-Universität München, 80336 Munich, Germany; 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; Center for Nanosciences München, 80799 Munich, Germany.
authors.forename: Dario
authors.initials: D
authors.lastname: Brack
authors.affiliation: Department of Cellular Physiology, Ludwig-Maximilians-Universität München, 80336 Munich, Germany; Center for Nanosciences München, 80799 Munich, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Ellrich
authors.affiliation: Department of Cellular Physiology, Ludwig-Maximilians-Universität München, 80336 Munich, Germany;
authors.forename: Beate
authors.initials: B
authors.lastname: Averbeck
authors.affiliation: Department of Cellular Physiology, Ludwig-Maximilians-Universität München, 80336 Munich, Germany; Center for Nanosciences München, 80799 Munich, Germany claudia.veigel@med.uni-muenchen.de.
authors.forename: Claudia
authors.initials: C
authors.lastname: Veigel
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D002478:Cells, Cultured; D002645:Chickens; D018995:Myosin Heavy Chains / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D002147:Calmodulin; C089785:myosin VI; D018995:Myosin Heavy Chains; D002118:Calcium
keywords: calmodulin; electron microscopy; unconventional myosin
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