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J. Biol. Chem., Vol. 283, Issue 8, 4520-4527, February 22, 2008

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Mechanism, Regulation, and Functional Properties of Dictyostelium Myosin-1B^*

Georgios Tsiavaliaris¹, Setsuko Fujita-Becker, Ulrike Dürrwang, Ralph P. Diensthuber, Michael A. Geeves^¶, and Dietmar J. Manstein

From the Institute for Biophysical Chemistry, OE 4350, Hannover Medical School, Carl-Neuberg-Strasse 1, D-30623 Hannover, Germany, the Department of Biophysics, Max Planck Institute for Medical Research, Jahnstrasse 29, D-69120 Heidelberg, Germany, and the ^¶Department of Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom

Myosin-1B is one of three long tailed class-1 myosins containing an ATP-insensitive actin-binding site in the tail region that are produced in Dictyostelium discoideum. Myosin-1B localizes to actin-rich structures at the leading edge of migrating cells where it has been implicated in the formation and retraction of membrane projections, the recycling of plasma membrane components, and intracellular particle transport. Here, we have used a combination of molecular engineering approaches to describe the kinetic and motile properties of the myosin-1B motor and its regulation by TEDS site phosphorylation. Our results show that myosin-1B is a low duty ratio motor and displays the fastest nucleotide binding kinetics of any of the Dictyostelium class-1 myosins studied so far. Different from Dictyostelium myosin-1D and myosin-1E, dephosphorylated myosin-1B is not inactivated but moves actin filaments efficiently, albeit at an up to 8-fold slower velocity in the in vitro motility assay. A further difference is that myosin-1B lacks the ability to switch between rapid movement and bearing tension upon physiological changes of free Mg²⁺ ions. In this respect, its motor properties appear to be more closely related to Dictyostelium myosin-2 and rabbit skeletal muscle myosin.

Received for publication, September 28, 2007 , and in revised form, November 21, 2007.

^* This work was supported by Deutsche Forschungsgemeinschaft Grants MA1081/11-1 (to D. J. M.) and TS 169/3-1 (to G. T.) and Wellcome Trust Grant 070021 (to M. A. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 49-511-532-8591; Fax: 49-511-532-5966; E-mail: gtsiaval{at}bpc.mh-hannover.de.

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