chapter  7
38 Pages

The Structure of Contractile Proteins

The physical alterations of the shape of the cell, its structure, motility and contractile ability are an attribute of the structure and organisation of the cytoskeletal machinery, of which the intermediate filaments (IF) (10 nm diameter), actin microfilaments (7 nm diameter), and microtubules are the important components. Actin microfilaments are polymers of F-and G-actin. These filaments are flexible, double-helical polymeric structures made up of F-actin strands. The G-actin subunits participate in binding to the myosin globular heads. G-actin also possesses ATP-or ADP-binding domains. Actin filaments have a defined polarity, which flows from the fact that the monomers themselves show a distinct polarity. In association with actin-binding proteins, the actin filaments form specialised structures. To these organised structures the cell owes its faculty of modulation of shape, motility, and other adhesionmediated phenomena. The reorganisation of actin cytoskeleton is also involved with plant cell division, differentiation, and light-induced plastid migration, among other cellular features (Staiger

et al.