| Myosins are actin-based molecular motors that use energy from ATP hydrolysis to perform work within the cell. On a cellular scale their influence is vast, driving intracellular trafficking, cell motility, contraction, and division. On a larger scale, myosins are integral to the developmental process, immunological response, vision, hearing, and muscle contraction.;Class 18 of the myosin superfamily has been implicated as a factor in clinically relevant roles as a support system for stromal cell differentiation (myosin-18A) and as a tumor suppressor (myosin-18B). Within mammalian cells, myosin-18A has been suggested to help maintain both the trans-Golgi structure and actin networks in the lamellipodia. However, biochemical analysis of myosin-18A suggests that it has markedly different properties than other myosins, namely that its ability to bind actin is insensitive to ATP. Furthermore, myosin-18 differs from other myosins by the presence of a PDZ protein-protein interacting domain at its N-terminus.;In this study, we investigated the biochemistry of Drosophila melanogaster myosin-18. Using an Sf9/baculoviral expression system, we probed the activities of this myosin from the perspective of its association with actin and ATP. This study suggests that myosin-18 is highly divergent from other molecular motors, with ATP-insensitive actin binding, and lack of nucleotide binding properties. These results suggest that some myosins may function more as actin tethers, and in this regard, may be more precisely defined as an actin binding protein. |
