Unconventional processive mechanics of non-muscle myosin IIB

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Abstract

Proper tension maintenance in the cytoskeleton is essential for regulated cell polarity, cell motility, and division. Non-muscle myosin IIB (NMIIB) generates tension along actin filaments in many cell types, including neuronal, cardiac, and smooth muscle cells. Using a three-bead optical trapping assay, we recorded NMIIB interactions with actin filaments to determine if a NMIIB dimer cycles along an actin filament in a processive manner. Our results show that NMIIB is the first myosin II to exhibit evidence of processive stepping behavior. Analysis of these data reveals a forward displacement of 5.4 nm and, surprisingly, frequent backward steps of -5.9 nm. Processive stepping along the long pitch helix of actin may provide a mechanism for disassembly of fascin-actin bundles. Forward steps and detachment are weakly force-dependent at all forces, consistent with rate-limiting and force-dependent ADP release. However, backward steps are nearly force-independent. Our data support a model in which NMIIB can readily move in both directions at stall, which may be important for a general regulator of cytoskeleton tension. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.

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Norstrom, M. F., Smithback, P. A., & Rock, R. S. (2010). Unconventional processive mechanics of non-muscle myosin IIB. Journal of Biological Chemistry, 285(34), 26326–26334. https://doi.org/10.1074/jbc.M110.123851

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