|Many types of cellular movement, such as pseudopod extension, vesicle transport and endocytosis are driven by myosin-actin interactions. A single eukaryotic cell may contain 10-15 different myosins, each specialized to drive one or more motile processes. My lab is focused on unraveling the signaling pathways that regulate myosin motor activity.
We are using as a model system the highly motile lower eukaryote Dictyostelium discoideum, since these cells are easy to grow in large quantities and are amenable to genetic manipulation. My lab has identified, purified and sequenced two protein kinases involved in myosin regulation, MHCK A and MIHCK, and these are the focus of our studies.
MHCK A phosphorylates and inhibits myosin II, the Dictyostelium version of the conventional muscle-type myosin. Surprisingly, MHCK A contains an unusual catalytic domain, that at present is known to exist only in MHCK A, two other Dictyostelium kinases and the mammalian elongation factor-2 kinase. Studies are underway to characterize the structural and biochemical properties of the atypical kinase domain.
place here MIHCK phosphorylates and activates the small single-headed myosin I isozymes, and is a close relative of the mammalian p21-activated kinase (PAK). MIHCK, like PAK, is activated by Cdc42 and Rac, two members of the Rho family of Ras-related GTPases. Analysis of cells in which the MIHCK gene has been disrupted and in which mutant forms of MIHCK have been expressed are in progress. By expressing a fusion protein of MIHCK with the green fluorescent protein (GFP), MIHCK has been localized to the plasma membrane and pseudopods of cells (see figure). Proteins that interact with MIHCK are being identified using yeast two-hybrid analysis.