Non-muscle myosin IIB exhibited processive stepping behavior with a forward displacement of 5.4 nm and frequent backward steps of -5.9 nm.
NMIIB is the first myosin II shown to exhibit processive stepping behavior, moving in both directions at stall, which may be important for regulating cytoskeleton tension.
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.
Norstrom et al. (2010) studied this question. Non-muscle myosin IIB (NMIIB) was evaluated on Processive stepping behavior and displacement. Non-muscle myosin IIB exhibited processive stepping behavior with a forward displacement of 5.4 nm and frequent backward steps of -5.9 nm.