Identification of a 33-kilodalton cytoskeletal protein with high affinity for the sodium channel

The voltage-sensitive sodium channel is an intrinsic membrane protein that is nonrandomly distributed in neurons, suggesting a possible interaction with other cellular constituents. In this study, we have directly tested the hypothesis that components of the cytoskeleton interact with sodium channels. Utilizing the methods of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and blot overlay, we have identified a 33-kilodalton cytoskeletal protein (p33) that binds 32P-labeled sodium channel purified from rat brain. This binding is a high-affinity (KD less than 1 nM) protein-protein interaction that is blocked by low concentrations of unlabeled sodium channels but is not blocked by monosaccharides, the complex glycoprotein fetuin, the transmembrane protein Na+-K+-ATPase, or bovine serum albumin. Levels of p33 are highest in lung and spleen while lower levels are found in brain, peripheral nerve, skeletal muscle, liver, and testes. This tissue distribution implies that the sodium channel may not be the only ligand for p33.