Interaction of brain spectrin (fodrin) with phospholipids

Binding of brain spectrin to frozen and thawed liposomes was studied, using a pelleting assay, as a function of lipid composition. Saturable binding was observed for all lipid mixtures that included aminophospholipids, as well as for the total lipid of synaptic plasma membranes. Binding was strong and saturable, with dissociation constants in the nanomolar range. There were two pH optima at ca. 6.0 and 7.5 and a sharp ionic strength optimum, corresponding to physiological solvent conditions. No competition could be detected with extraneous globular proteins, serum albumin, and hemoglobin. The results imply a strong, direct interaction between brain spectrin and the neuronal plasma membrane in the cell.