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First published online January 27, 2006
doi: 10.1242/10.1242/jcs.02774
Research Article |
1 Abteilung Biophysik, Max-Planck Institut für medizinische Forschung, Jahnstr. 29, 69120 Heidelberg, Germany
2 Dartmouth College, Department of Chemistry, 6128 Burke Laboratory, Hanover, NH 03755, USA
3 Institut für Biophysikalische Chemie, OE 4350, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30623 Hannover, Germany
4 Department of Biosciences, University of Kent, Canterbury CT2 7NJ, UK
* Author for correspondence (e-mail: manstein{at}bpc.mh-hannover.de)
Accepted 19 October 2005
Class I myosins are single-headed motor proteins, implicated in various motile processes including organelle translocation, ion-channel gating, and cytoskeleton reorganization. Here we describe the cellular localization of myosin-IE and its role in the phagocytic uptake of solid particles and cells. A complete analysis of the kinetic and motor properties of Dictyostelium discoideum myosin-IE was achieved by the use of motor domain constructs with artificial lever arms. Class I myosins belonging to subclass IC like myosin-IE are thought to be tuned for tension maintenance or stress sensing. In contrast to this prediction, our results show myosin-IE to be a fast motor. Myosin-IE motor activity is regulated by myosin heavy chain phosphorylation, which increases the coupling efficiency between the actin and nucleotide binding sites tenfold and the motile activity more than fivefold. Changes in the level of free Mg2+ ions, which are within the physiological range, are shown to modulate the motor activity of myosin-IE by inhibiting the release of adenosine diphosphate.
Key words: Dictyostelium discoideum, Phagocytosis, Phosphorylation, TEDS, Mg2+ concentration
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