Evolutionarily conserved short linear motifs drive actin filament binding

Regulation of the actin cytoskeleton by actin-binding proteins is essential for cellular homeostasis, and the mode of actin binding determines the activity of actin-binding proteins. Here we identify a 'short linear actin filament-binding motif' (SFM) based on the cryo-electron microscopy structure of the ITPKA-actin filament complex. Using the computational pipeline SLiMFold, we discovered 103 human proteins containing SFMs with diverse cellular roles. Phylogenetic analysis suggests that SFMs arose de novo and are conserved across eukaryotes, exhibiting actin filament-binding affinities of 2-12 µM. Critical residues mediating binding and modulating affinity were defined, and the cryo-electron microscopy structures of two SFM-actin filament complexes revealed that SFM binding decreases actin-filament stiffness. These findings indicate that SFMs regulate actin-filament conformation and serve as anchoring modules that connect actin dynamics to a broad variety of cellular functions, providing a framework for understanding the actin-associated roles of numerous proteins.