Unconventional processive mechanics of non-muscle myosin IIB.
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.
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, USA.
Melanie F
MF
Norstrom
Philip A
PA
Smithback
Ronald S
RS
Rock
D008841:Actin Cytoskeleton / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002645:Chickens; D003599:Cytoskeleton / Q000502:physiology; D055595:Mechanical Phenomena; D008840:Microfilament Proteins / Q000378:metabolism; D009068:Movement; D024501:Nonmuscle Myosin Type IIB / Q000378:metabolism*
D002352:Carrier Proteins; D008840:Microfilament Proteins; C020324:fascin; D024501:Nonmuscle Myosin Type IIB