Cytoplasmic Contractile Proteins

Abstract

Cytoplasmic contractile proteins have been studied extensively since the late 1960ies, when they were recognized as major components of the cytoplasm of essentially all eukaryotic cells. However, cytoplasmic contractility was considered an important property of living cells already 150 years ago, when the concept of the cell as the unit of life was first emerging. In 1835, Dujardin proposed that the cytoplasm is structured and has both elastic and contractile properties. He described the sticky material that emerges from squashed cells as a homogeneous, hyahne, living substance (“gelée vivante”) and named it the “sarcode”. Durjadin’s idea of the homogenous sarcode was replaced at the turn of the century by a new concept which viewed the cytoplasm as a heterogenous and highly structured substance. Observations during the first half of this century added the notion that the cytoplasm has a characteristic “viscosity” (Heilbrunn 1926). However, once the complexities of the relationship between the mechanical and contractile properties of the cytoplasm and its supramolecular architecture were realized, the thought that the cytoplasm could be characterized by a single physical parameter, its viscosity, was abandoned. In 1939, Lewis developed the remarkably accurate view that the cytoplasm is pervaded by “extremely large and asymmetrical molecules which presumably form long fibers on gelation” and also can exert “contractile tension”.