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Originally published as Biophys J. BioFAST on October 8, 2004.
doi:10.1529/biophysj.104.045245
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Biophysical Journal 88:384-391 (2005)
© 2005 The Biophysical Society

Mammalian Class I Myosin, Myo1b, Is Monomeric and Cross-Links Actin Filaments as Determined by Hydrodynamic Studies and Electron Microscopy

Walter F. Stafford *, Matt L. Walker {dagger}, John A. Trinick {dagger} and Lynne M. Coluccio *

* Boston Biomedical Research Institute, Watertown, Massachusetts; and {dagger} Asbury Centre for Structural Molecular Biology and School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom

Correspondence: Address reprint requests to Lynne M. Coluccio, PhD, Boston Biomedical Research Institute, 64 Grove St., Watertown, MA 02472. Tel.: 617-658-7784; Fax: 617-972-1761; E-mail: coluccio{at}bbri.org.

The class I myosin, Myo1b, is a calmodulin- and actin-associated molecular motor widely expressed in mammalian tissues. Analytical ultracentrifugation studies indicate that Myo1b purified from rat liver has a Stokes radius of 6.7 nm and a sedimentation coefficient, s20,w, of 7.0 S with a predicted molar mass of 213 kg/mol. These results indicate that Myo1b is monomeric and consists primarily of a splice variant having five associated calmodulins. Molecular modeling based on the analytical ultracentrifugation studies are supported by electron microscopy studies that depict Myo1b as a single-headed, tadpole-shaped molecule with outer dimensions of 27.9 x 4.0 nm. Above a certain Myo1b/actin ratio, Myo1b bundles actin filaments presumably by virtue of a second actin-binding site. These studies provide new information regarding the oligomeric state and morphology of Myo1b and support a model in which Myo1b cross-links actin through a cryptic actin-binding site.




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[Abstract] [Full Text] [PDF]


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