Assembly of Acanthamoeba Myosin-II Minifilaments. Model of Anti-parallel Dimers Based on EM and X-ray Diffraction of 2D and 3D Crystals

Assembly of Acanthamoeba Myosin-II Minifilaments. Definition of C-terminal Residues Required to Form Coiled-coils, Dimers, and Octamers

“…Sedimentation equilibrium does not reveal the geometry of these dimers, but a dramatic difference in the crystal form obtained for 15T and 15TC versus 15R suggests a different packing arrangement between these constructs. 20 Since both the tailpiece and residues between 1381 and 1393 are required for antiparallel dimerization, we hypothesize that the tailpiece binds its partner rod within this sequence, as expected from w15 nm overlap observed in electron micrographs of rotary-shadowed samples. 1 Residues 1381-1393 (heptads 13 and 14) and the tailpiece are necessary but not sufficient to form antiparallel dimers.…”

“…Nevertheless, 12T is sufficiently well folded to crystallize at high concentration in the presence of PEG 8000. 20 However upon addition of one more heptad to 14T to form 15T, dimers are ten times more stable. Sedimentation equilibrium experiments showed Oligomeric States of Myosin-II that constructs 15T, 15TC, and 15R all assemble into dimers with similar affinity in low salt.…”

Structural basis for the assembly of the mitotic motor Kinesin-5 into bipolar tetramers

“…The bipolar organization of Kinesin-5 resembles that of the bipolar class 2 myosin filament that drives the sliding filament mechanism of muscle contraction, cytokinesis and other forms of motility in non-muscle cells (Huxley, 1963; Turbedsky et al, 2005; Billington et al, 2013). However, whereas varying numbers of myosin-2 motors can assemble into filaments of variable length, all capable of pulling actin filaments inward, we propose that the unique structure of the BASS domain allows it to organize four Kinesin-5 subunits into stable, mechanically robust bipolar tetramers of uniform length, that represent functional units capable of bearing both compressive and tensile forces as they slide cross-linked MTs outward, or resist their outward sliding.…”

Actin Rings of Power

“…ROCK also phosphorylates the myosin phosphatase-targeting subunit of MLCP, thereby blocking its phosphatase function and thus preventing it from deactivating myosin (Feng et al, 1999;Kimura et al, 1996;Murá nyi et al, 2005). The phosphorylation of myosin regulatory light chain, besides turning on myosin motor activity, also promotes the formation of bipolar myosin mini-filaments through tail-to-tail association, which can then further mature into thick filaments found, for example, in the sarcomere of skeletal muscles (Niederman and Pollard, 1975;Ricketson et al, 2010;Scholey et al, 1980;Turbedsky et al, 2005). In contrast, phosphorylation of the heavy chain of myosin by kinases, such as protein kinase C (PKC), reduces myosin filament assembly (Dulyaninova et al, 2005;Egelhoff et al, 1993).…”