Tropomyosin‐Mediated Regulation of Cytoplasmic Myosins

• Published in: Traffic (Copenhagen, Denmark) Denmark), 2016-08, Vol.17 (8), p.872-877
• Main Authors: Manstein, Dietmar J., Mulvihill, Daniel P.
• Format: Article
• Language: English
• Subjects: actin; Actin Cytoskeleton - metabolism; Actins - metabolism; allostery; Animals; Cytoplasm - metabolism; cytoskeleton; Cytoskeleton - metabolism; Humans; isoforms; Metazoa; multigene family; myosin; Myosins - metabolism; protein complex; tropomyosin; Tropomyosin - metabolism
• ISSN: 1398-9219; 1600-0854
• DOI: 10.1111/tra.12399

The ability of the actin‐based cytoskeleton to rapidly reorganize is critical for maintaining cell organization and viability. The plethora of activities in which actin polymers participate require different biophysical properties, which can vary significantly between the different events that often occur simultaneously at separate cellular locations. In order to modify the biophysical properties of an actin polymer for a particular function, the cell contains diverse actin‐binding proteins that modulate the growth, regulation and molecular interactions of actin‐based structures according to functional requirements. In metazoan and yeast cells, tropomyosin is a key regulator of actin‐based structures. Cells have the capacity to produce multiple tropomyosin isoforms, each capable of specifically associating as copolymers with actin at distinct cellular locations to fine‐tune the functional properties of discrete actin structures. Here, we present a unifying theory in which tropomyosin isoforms critically define the surface landscape of copolymers with cytoplasmic β‐ or γ‐actin. Decoration of filamentous actin with different tropomyosin isoforms determines the identity and modulates the activity of the interacting myosin motor proteins. Conversely, changes in the nucleotide state of actin and posttranslational modifications affect the composition, morphology, subcellular localization and allosteric coupling of the associated actin‐based superstructures. The metazoan actin‐based cytoskeleton facilitates an assortment of diverse cellular functions. This is made possible by the members of the tropomyosin multigene family, which at discrete cellular locations form well‐defined copolymers with unique functional properties. Here, we present a unifying theory in which the tropomyosin isoform associating with the actin defines the surface landscape of the copolymer to determine the identity and activity of myosin motors that move upon it.