Fig. 1

Schematic representation of the actinin dimer. The domain organization of the anti-parallel actinin dimer is depicted schematically in the closed conformation as observed in the X-ray crystallographic structure of the human actinin-2 [4]. In each subunit two calponin homology (CH) domains make up the N-terminal actin-binding domain (ABD). The rod domain composed of four spectrin-like repeats (SLR1-4) makes up the bulk of the dimer interface. The carboxyl terminal calmodulin-like (CaM) domain is made up of two pairs of EF-hand motifs (EF1/2 and EF3/4). EF1/2 binds Ca⁺⁺ in some actinins [1]. EF3/4 from one subunit interacts with the “neck” region between the ABD and first SLR of the opposing monomer (depicted as a line) [3]. This interaction clamps the protein into a closed conformation that is thought to be opened up by phospholipid binding to the ABD [4, 3]