Actinin

Actinin is a microfilament protein. The functional protein is an anti-parallel dimer, which cross-links the thin filaments in adjacent sarcomeres, and therefore coordinates contractions between sarcomeres in the horizontal axis. Alpha-actinin is a part of the spectrin superfamily. This superfamily is made of spectrin, dystrophin, and their homologous and isoforms. In non-muscle cells, it is found by the actin filaments and at the adhesion sites.The lattice like arrangement provides stability to the muscle contractile apparatus. Specifically, it helps bind actin filaments to the cell membrane. There is a binding site at each end of the rod and with bundles of actin filaments.

The non-sarcomeric alpha-actinins, encoded by ACTN1 and ACTN4, are widely expressed. ACTN2 expression is found in both cardiac and skeletal muscle, whereas ACTN3 is limited to the latter. Both ends of the rod-shaped alpha-actinin dimer contain actin-binding domains. Six different proteins are produced from four alpha-actinin encoding genes.These six proteins can further be divided into two different groups: muscle (calcium insensitive) and non-muscle cytoskeletal (calcium sensitive) isoforms.