SPTBN1 is a major constituent of the erythrocyte skeleton, accounting for 25% of the total membrane protein and 75% of the cytoskeletal mass. It is associated with the cytoplasmic surface of the membrane by attachment to ankyrin, a peripheral membrane protein. The membrane skeleton influences several cellular properties such as cell shape, restriction of mobility of the integral membrane protein exposed at the cell surface, and transmembrane movement of phospholipids and cholesterol. While the simplest form of SPTBN1 in solution is an alpha-beta heterodimer, SPTBN1 can undergo self-association in various conditions to form a tetramer of alpha2-beta2. In recent years a large number of SPTBN1-like molecules have been found in non-erythroid cells. These proteins are known by such different names as fodrin, CBP I, calspectin and TW 260/240.