CryoEM Reconstruction of Yeast ADP-Actin Filament at 2.5 Å resolution. A comparison with mammalian and avian F-actin

The core component of the actin cytoskeleton is the globular protein G-actin, which reversibly polymerises into filaments (F-actin). Budding yeast possesses a single actin which shares 87-89% sequence identity with vertebrate actin isoforms. Previous structural studies indicate very close overlap of main-chain backbones. Intriguingly however, substitution of yeast ACT1 with vertebrate β-cytoplasmic actin severely disrupts cell function and substitution with a skeletal muscle isoform is lethal. Here we report a 2.5 Å structure of budding yeast F-actin. Previously unresolved side-chain information now highlights four main differences in the comparison of yeast and vertebrate ADP F-actins: a more open nucleotide binding pocket; a more solvent exposed C-terminus; a rearrangement of intersubunit binding interactions in the vicinity of the D-loop and changes in the hydrogen bonding network in the vicinity of histidine 73 (yeast actin) and methyl-histidine 73 (vertebrate actin).