Actin's Many Modes

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Science  05 Nov 2010:
Vol. 330, Issue 6005, pp. 733
DOI: 10.1126/science.330.6005.733-b

Actin is one of the most abundant eukaryotic proteins. It polymerizes to form filamentous actin (F-actin), which plays a key role in regulating cell shape, polarity, and force generation. The sequence of eukaryotic actin is highly conserved over evolution. One explanation for this is that the many functions of actin require a large degree of biochemical and structural plasticity and heterogeneity. Such a large variety of states puts pressure on the majority of amino acid residues. To better understand the structural polymorphism of F-actin, Galkin et al. used electron microscopy of unmodified, frozen-hydrated actin filaments. They observed multiple structural states in the same filament (below), which requires that filaments form cooperative units. These states reveal allosteric coupling between certain structural features that contribute to plasticity both within and between actin subunits. A number of disease-causing mutations in the human ACTA1 gene that encodes skeletal muscle actin affect residues in the most dynamic structural elements of the protein. Actin plasticity is probably required to accommodate its multiple interactions and functions. The authors suggest that the allosteric coupling associated with this plasticity has played an important role in preventing sequence divergence.

Nat. Struct. Mol. Biol. 10.1038/nsmb.1930 (2010).

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