WCell motility is a dynamic process involving the coordinated regulation of a multitude of cytoskeletal proteins. Central to this phenomenon are the proteins myosin and actin, which interact to generate the force driving fundamental cellular processes such as cytokinesis, muscle contraction, phagocytosis, vesicular trafficking and polarized cell growth. Myosins constitute a superfamily of motor proteins consisting of at least fifteen (numbered I - XV based on their order of discovery) distinct classes. Myosins are ubiquitous in eukaryotes and have been characterized in Arabidopsis, C. elegans, Toxoplasma, Drosophilia, Dictyostelium and humans. Certain vertebrate cells express nearly a dozen different myosins representing seven different classes.

Despite their broad evolutionary distribution, almost all myosins share in common a peptide heavy chain that can be loosely subdivided into three functional domains: an amino-terminal head or motor domain, a neck domain that binds one or more light chains and a carboxy-terminal tail. The head domain contains sites for binding actin filaments and ATP. Consequently this domain of the molecule can motor along existing actin filaments within the cell fueled by hydrolysis of ATP. The neck domain is structurally linked to the motor region and appears to tightly regulate the mechanochemical activities of myosin in response to changes in Ca2+ and light chain dissociation. The tail domain is structurally diverse and can possess sites for self-association, for binding other proteins or for binding to phospholipids and organelles.

The focus of my research is to characterize the molecular properties of Myosin-V in vertebrates. This two-headed myosin binds multiple calmodulin light chains in the neck region and is a strong candidate for an organelle motor in a variety of cell types. We are currently investigating the possible role of myosin-V in the transport of melanosomes (membrane-bound pigment containing organelles) to dendritic processes in mouse melanocytes. Our approach has been to examine melanosome motility in cultured melanocytes exposed to factors that selectively inhibit cytoskeleton proteins. We are also examining whether melanosomes can move relative to actin filaments using in vitro motility assays. Results from these studies demonstrate that myosin-V is localized on purified melanosomes and is capable of transporting these organelles along actin filaments in vitro. In addition, we are examining how the different domains of myosin-V contribute to the in vivo function of this complex motor protein. In this approach various domains of the myosin-V heavy chain were linked to green fluorescent protein and the intracellular localization of GFP-myosin constructs was examined in transfected melanocytes. The GFP studies also revealed the tail domain of this motor molecule is responsible for the association of myosin-V with centrosomes raising the possibility that myosin has a distinct role in cell division. Future studies are planned for identifying the target(s) of myosin-V in centrosomes.

Selected Publications

Wolenski, J.S. (1995) Regulation of calmodulin-binding myosins. Trends in Cell Biol., 5: 310-316

Wang, F.S., J.S. Wolenski, R.E. Cheney, M.S. Mooseker, and D.G. Jay. (1996) Function of Myosin-V in Filopodial Extension of Neuronal Growth Cones. Science. 273:660-663.

Espreafico, E.M., D.E. Coling, V. Tsakraklides, K. Krogh, J. S. Wolenski, G. Kalinec and B. Bachar. (1998) Localization of Myosin-V in the Centrosomes. Proceedings of the National Academy of Sciences (in press).

top