Certain myosin isoforms (i.e. myosin II) form bipolar assemblies via the extended coiled-coil domains in the heavy chains (see also “thick filaments”). Actin “thin filaments”
with opposite polarity associate with thick filaments to create
contractile bundles that can be found in both muscle and nonmuscle
cells. The concerted movement of the myosin heads generates the forces
needed for contraction and causes the adjacent actin filaments to
‘slide’ past each other (see Figure Actin-myosin contraction in muscle cells). Evidence for the sliding mechanism of force generation, comes largely from in vitro
reconstitution studies, particularly the sliding filament assay created
by Kron and Spudich [1, 2]. This assay and subsequent variations of it
demonstrated the ability of myosin to bind and slide individual actin
filaments [1, 2] and have further elucidated the biophysical properties
of this action [3].
Contractile bundles vary in thickness and
have been shown to contain anywhere between 10 to 300 individual actin
filaments [4]. These bundles are stabilized throughout the bundle and at
the filament ends by a number of accessory proteins (e.g. α-actinin, titin, components of the focal adhesion
complex). Contractile bundles are also crucial for generating both
traction and protrusion forces in motile cells and they are involved
during cell division (e.g. cytokinesis).
For studies which
investigate the role of cell contraction and motility, contractile
force can be inhibited using small molecules such as blebbistatin [5].
Ĉ ď Sruthi Jaganathan, Jan 16, 2012, 12:44 AM Ĉ ď Sruthi Jaganathan, Jan 16, 2012, 12:44 AM
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