Actin does pretty well on its own, but with tropomyosin as wing-man it is a force to be reckoned with. Tropomyosin is necessary for our muscles to contract, and recently was found to be important in vesicle and organelle transport.
Molecular motors such as myosin are frequently described as processive or nonprocessive, or how well they stay on and walk along the actin filaments (or microtubules). The class of myosin V motors is made of unconventional myosins that function in intercellular cargo trafficking. Several class V myosins are nonprocessive, including the budding yeast Myo2p myosin that functions in vesicle and organelle transport. A recent paper describes results on the requirements that make this myosin processive within a yeast cell. Hodges and colleagues found that bare actin filaments cause Myo2p to be nonprocessive, but the addition of tropomyosin, a protein that binds along the length of actin, to the filament allowed the Myo2p to remain strongly attached to actin. In the images above, a schematic shows the attachment of a fluorescent quantum dot to the Myo2p motor (left). The quantum dot (red, yellow arrow) could then be tracked as the motor moved along an actin-tropomyosin filament (green).
Alex R. Hodges, Elena B. Krementsova, Carol S. Bookwalter, Patricia M. Fagnant, Thomas E. Sladewski, & Kathleen M. Trybus (2012). Tropomyosin Is Essential for Processive Movement of a Class V Myosin from Budding Yeast Current Biology, 22 (15), 1410-1416 DOI: 10.1016/j.cub.2012.05.035
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