Combining Electron Microscopy and X-Ray Crystallography Data to Study the Structure of F-Actin and its Implications for Thin-Filament Regulation In Muscle
Actin filaments (F-actin) are found in nearly all eukaryotic cells as elements of the cytoskeleton. They also play a central role in various types of contractility, motility and transport. F-actin is a helical polymer composed of identical globular subunits, each of which contains 375 amino acids. The atomic structure of the monomer (G-actin; 42 kD) has recently been determined from a complex of the monomer and DNase (Kabsch et al., 1990). The monomer structure, shown in figure 1, has two major domains (historically these were termed “large” and “small”, but it is now known that they are of nearly the same size) which are each divided into two subdomains. Subdomain 1 contains the N- and C-termini of the polypeptide chain. The prominent cleft between the two major domains is the site of nucleotide binding. Knowledge of the precise arrangement of the actin subunits within F-actin would be helpful in understanding the function of F-actin at the molecular level.
KeywordsActin Filament Thin Filament Helix Axis Fluorescence Energy Transfer Myosin Subfragment
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