Cryo-electron microscopy structures of F-actin reveal that terminal subunits at the free barbed end adopt a flat conformation, whereas those at the free pointed end adopt a twisted conformation.
The structures reveal how the ends of actin filaments differ from the middle, providing a mechanistic basis for subunit addition, dissociation, and capping protein interactions.
The barbed and pointed ends of the actin filament (F-actin) are the sites of growth and shrinkage and the targets of capping proteins that block subunit exchange, including CapZ at the barbed end and tropomodulin at the pointed end. We describe cryo-electron microscopy structures of the free and capped ends of F-actin. Terminal subunits at the free barbed end adopt a "flat" F-actin conformation. CapZ binds with minor changes to the barbed end but with major changes to itself. By contrast, subunits at the free pointed end adopt a "twisted" monomeric actin (G-actin) conformation. Tropomodulin binding forces the second subunit into an F-actin conformation. The structures reveal how the ends differ from the middle in F-actin and how these differences control subunit addition, dissociation, capping, and interactions with end-binding proteins.
Carman et al. (Thu,) reported a other. Cryo-electron microscopy structures of F-actin reveal that terminal subunits at the free barbed end adopt a flat conformation, whereas those at the free pointed end adopt a twisted conformation.
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