Salt and temperature-dependent conformation changes in spectrin from human erythrocyte membranes

ORD and CD measurements of spectrin, in both the dimer and tetramer association state, indicate a high proportion of alpha-helix in this protein. At temperatures below 27 degrees C and in 0.1 M NaCl, the tetramer has an apparent helix content of 73% and the dimer, 68%. The conformation of both states is dependent on salt concentration and temperature. Low ionic strength solutions of spectrin display lowered sedimentation coefficients and a decreased apparent helix content, indicating perhaps a slight refolding and expansion of the molecule. In addition, spectrin in low ionic strength solutions undergoes a broad temperature-dependent transition spread from 20 to 50 degrees C, while in the presence of salt the transition is sharp and centered on 49 degrees C. The temperature-dependent changes in low ionic strength solutions appear to parallel the dissociation of tetramer to dimer.