Each myosin motor protein possesses ATPase activity and functions in a cyclical manner that couples ATP binding and hydrolysis to a conformational change in the protein. This process is known as the ‘powerstroke cycle’… Read more…
Several myosin isoforms have been found in eukaryotes, each differing in the type of heavy and light chains they are composed of. All myosins are composed of a diverse ‘tail’ domain at their carboxy terminus and an evolutionarily conserved globular ‘head’ domain at their amino terminus… Read more…
The most commonly described motor proteins belong to the Myosin superfamily. Myosin II can form higher order assemblies via the extended coiled-coil domains in the heavy chains and is known for enabling contraction in muscle cells when in complex with actin filaments. In non-muscle cells, actin filaments form an internal track system for cargo transport that is […]
Myosin light chain kinase is activated by calmodulin in response to an increase in intracellular calcium. It then goes on to phosphorylate regulatory myosin light chains at residues serine 19 and threonine 18. These phosphorylations enhance the ATPase activity of actin-activated myosin and so promotes myosin-driven contraction… Read more…
The kinesin superfamily of proteins represents a large class of motor proteins that carry cargo along microtubules. Conventional kinesins move along microtubule filaments in a manner that resembles human walking. This has been described as an asymmetric ‘hand-over-hand’ mechanism where one head domain steps forward ~16.2nm whilst the other head remains stationary. For each step the head domains take, […]
Movement of myosin-X is driven by ATP hydrolysis, in a unique mechanism that resembles walking or stepping. This movement is known to occur preferentially on actin bundles rather than single actin filaments. Although it is essentially a forward movement, evidence indicates that the protein may also take side-steps. This may be carried out as a […]
Tension-dependent actin polymerization and assembly of stress fibers is influenced by many factors, including differences in substrate composition, rigidity, cell membrane phospholipids, external force, as well as by strength of the connection(s) between actin filaments and the adhesion. Each of these cues converges at the level of the Rho family of GTPases and their effector substrates… Read more…
Once the bundled actin filaments in dorsal stress fibers fully interact with the transverse arc filaments, the bundles become aligned and completely ‘fuse’ to create a cohesive contractile structure that is the ventral stress fiber… Read more…
Transverse arcs filaments are thought to supply the dorsal stress fibers with filaments of mixed polarity as they are assembled; how this is achieved is relatively unknown, but based on experiments using purified components, permeabilized cells and live cells, it has been suggested that myosin bundles may recruit the filaments and facilitate polarity sorting. In […]
Recent data suggests that ventral stress fibers are created by reorganizing pre-existing dorsal stress fibers and transverse arcs.Other contrasting models for the formation of ventral stress fibers not covered in this resource include annealing or fusion of short actin bundles that are associated with focal adhesions… Read more…
