Spectrin is the major constituent of the cytoskeletal network underlying the erythrocyte plasma membrane. It associates with band 4.1 and actin to form the cytoskeletal superstructure of the erythrocyte plasma membrane. Composed of nonhomologous chains, alpha and beta, which aggregate to form dimers, tetramers, and higher polymers. This complex is anchored to the cytoplasmic face of the plasma membrane via another protein, ankyrin, which binds to beta-spectrin and mediates the binding of the whole complex to a transmembrane protein band 3. The interaction of erythrocyte spectrin with other proteins through specific binding domains lead to the formation of an extensive subplasmalemmal meshwork which is thought to be responsible for the maintenance of the biconcave shape of human erythrocytes, for the regulation of plasma membrane components and for the maintenance of the lipid asymmetry of the plasma membrane. Belongs to the spectrin family.