Actin filaments are dynamic protein-fibres in the cell built from single actin proteins. Many cellular functions, including cell movement, are regulated by constant filament assembly and disassembly. The disassembly phase is initiated by the release of a phosphate group from inside the filament, but the details of this process have puzzled scientists since decades. Researchers from the Max Planck Institute of Molecular Physiology in Dortmund and the Max Planck Institute of Biophysics in Frankfurt have joined forces to precisely identify a region in actin that functions as a “molecular backdoor” for phosphate to exit through. Using cryo- electron microscopy and molecular dynamics simulations, the scientists determined the mechanism of phosphate release from actin filaments. They also described how a distorted backdoor enables the faster release of phosphate from an actin mutant linked to nemaline myopathy, a severe muscle disease. more