Actin in a twist

Abstract

How monomers of the cytoskeletal protein actin join to form the stable polymers crucial to muscle contraction and cellular motility has been a long-standing question. A state-of-the-art approach provides an answer. Actin is found in almost all eukaryotic cells in two forms: filamentous F-actin, which drives many cellular processes including cell motility and muscle contraction, and the monomer from which it is produced, globular or G-actin. The structural changes that occur during G- to F-actin transition have remained elusive as previous models for the polymer have been based largely on the structure of G-actin. Now the structure of F-actin has been determined at high resolution. The structure reveals that the two major domains, which form a propeller-like twist in G-actin, are untwisted and the molecule is flat in F-actin. The flattening together with the helical disposition stabilizes the intra- and inter-strand contacts. The conformational G-to-F transition is totally consistent with the previous biochemical studies of actin.