Near-Atomic Resolution for One State of F-Actin

Actin functions as a helical polymer, F-actin, but attempts to build an atomic model for this filament have been hampered by the fact that the filament cannot be crystallized and by structural heterogeneity. We have used a direct electron detector, cryo-electron microscopy, and the forces imposed on actin filaments in thin films to reconstruct one state of the filament at 4.7 Å resolution, which allows for building a reliable pseudo-atomic model of F-actin. We also report a different state of the filament where actin protomers adopt a conformation observed in the crystal structure of the G-actin-profilin complex with an open ATP-binding cleft. Comparison of the two structural states provides insights into ATP-hydrolysis and filament dynamics. The atomic model provides a framework for understanding why every buried residue in actin has been under intense selective pressure. •Cryo-EM reconstruction of F-actin at 4.7 Å resolution has been determined•Structural homogeneity achieved by large forces present during cryo-EM preparation•A tilted stated of F-actin found in the absence of forces when thicker ice is used•Together, insights emerged into the structural dynamics of actin Actin is one of the most abundant and ubiquitous proteins, at the same time that it is one of the most highly conserved. Galkin et al. describe a new atomic model for one state of the actin filament as determined by cryo-EM.