aktiinin

Aktiinin, known in English as actinin, is a family of actin-binding proteins that crosslink and organize actin filaments in the cytoskeleton. They function as dimers with an N-terminal actin-binding domain, a central rod domain formed by coiled-coil segments, and a C-terminal pair of calmodulin-like EF-hand motifs. Most actinins form antiparallel dimers, enabling them to bridge two actin filaments and connect them to membrane complexes and other cytoskeletal elements. This architecture supports a range of cellular processes, including maintenance of cell shape, mechanical resilience, adhesion, and the organization of contractile structures in muscle.

In vertebrates, four actinin genes encode distinct isoforms with tissue preferences: ACTN1 and ACTN4 encode non-muscle actinins found in many cell types; ACTN2 (α-actinin-2) is expressed in cardiac and skeletal muscle; ACTN3 (α-actinin-3) is predominantly found in fast-twitch skeletal muscle fibers. Actinins participate in structures such as Z-discs in striated muscle, dense bodies in smooth muscle, focal adhesions, and cell–cell junctions, interacting with other cytoskeletal and signaling proteins like vinculin, talin, and spectrin.

Genetic variants and altered expression of actinins are linked to human disease. Mutations in ACTN1 have been associated with inherited macrothrombocytopenia, a platelet disorder characterized by abnormally large platelets and reduced platelet counts. ACTN4 mutations can cause autosomal dominant familial focal segmental glomerulosclerosis (FSGS), a kidney disease. Variants in ACTN2 and ACTN3 have been linked to cardiomyopathy and differences in muscle performance, respectively; ACTN3 deficiency is common in humans and related to reduced sprint performance, with some studies noting potential endurance-related effects. Overall, aktiinin family members are essential for the dynamic organization of the actin cytoskeleton across tissues.