Role of Dynamic and Cooperative Conformational Changes in Actin Filaments

The amino acid sequence of actin is highly conserved in most eukaryotic organisms, and each cell typically expresses only one or two homologous actin isoforms. Yet, actin filaments play important roles in a number of diverse activities in each cell. Each of those actin functions depends on interactions with a specific set of actin binding proteins. In a number of cases, local biochemical signaling to regulate the activities of actin binding proteins has been shown to contribute to the spatial and temporal regulation of those interactions, but not all aspects of the local regulations of the interactions can be explained by local biochemical signaling. Interactions with actin binding proteins or mechanical force induce conformational changes to actin protomers in the filaments, and the resultant conformational changes often propagate to neighboring actin protomers in the filament. We propose that those cooperative conformational changes in actin filaments may contribute to functional differentiation of actin filaments by specifying which actin binding protein to bind, enabling each actin filament to perform different functions within a common cytoplasm. In addition, we discuss the possible involvement of such cooperative conformational changes of actin filaments in interaction with myosin to generate force.