Schematic of the domain structure of alpha-actinins (a). Alpha-actinins are composed of an actin-binding domain (ABD), four spectrin repeats (SRs), and a calmodulin (CaM)-like domain. ABDs are composed of two calponin homology (CHs) domains (CH1 and CH2). CaM-like domains are composed of two EF-hand motifs. Schematic of actin bundling with alpha-actinins (b). Actinins form an anti-parallel dimer, and homodimers of actinins bundle actin fibers by interacting with the ABD. Schematic of interactions between actin fibers and cell membranes (c). Actin fibers bundled with actinins directly or indirectly interact with the cell membrane through integrins.